GB2580726A

GB2580726A - Underwater detection apparatus and underwater detection method

Info

Publication number: GB2580726A
Application number: GB1909865.6A
Authority: GB
Inventors: Okunishi Akira; Nagai Sanae; Saetre Roger; Dubuis Jerome
Original assignee: Furuno Electric Co Ltd
Current assignee: Furuno Electric Co Ltd
Priority date: 2018-07-11
Filing date: 2019-07-10
Publication date: 2020-07-29
Anticipated expiration: 2039-07-10
Also published as: GB201909865D0; GB2580726B

Abstract

An underwater detection apparatus for detection of mobile targets, such as schools or shoals of fish, as well as targets such as trawling equipment, nets and otter boards, which have zero velocity relative to a fishing boat that tows them. The apparatus includes a transmitter and a receiver, which receives reflected transmission waves and generates a reception signal. A Doppler shift module calculates the frequency shift of the reflected wave relative to the transmission wave. A first signal processor retrieves an echo signal from the reception signal based on the frequency shift amount. A second signal processor retrieves an echo signal independently of the doppler shift. An image signal generation module (14) that creates a target echo image of static and mobile targets based on doppler corrected and non-corrected signals respectively.

Description

UNDERWATER DETECTION APPARATUS AND UNDERWATER DETECTION

METHOD

Technical Field

[0001] The present disclosure relates to an underwater detection apparatus and an underwater detection method, which detect an underwater target object.

Background of the Invention

[0002] For example, JP4798826B2 discloses a transducer which transmits underwater an ultrasonic beam as a transmission wave to scan an underwater area, and generates a reception signal from a reception wave including a reflection of the transmission wave on an underwater target object. Moreover, JP5089319B2 discloses an underwater detection apparatus (sonar) which generates an image signal for displaying underwater information within a scanning area as an image based on a reception signal generated by a transducer.

[0003] In the underwater detection apparatus using the transducer disclosed in JP4798826B2 and the underwater detection apparatus disclosed in JP5089319B2, an image signal of an echo of the underwater target object, such as a school of fish, is generated as the underwater information. Then, based on the image signal, the echo of the target object, such as the school of fish, is displayed on a display unit as the image.

[0004] The transducers and the underwater detection apparatus as disclosed in JP4798826B2 and JP5089319B2 are used in a ship. The transducer mounted on the ship transmits the transmission wave, and when the reception wave reflected at the target object is received, a Doppler shift in which a frequency of the reception wave shifts from a frequency of the transmission wave occurs according to a ship speed and an incoming direction of the reception wave. Therefore, the underwater detection apparatus corrects the reception signal from the transducer based on an amount of the Doppler shift of the echo of the target object to acquire an echo signal, and generates the image signal for displaying the echo on the display unit. Therefore, the underwater detection apparatus can detect the target object, such as the school of fish, of which a ground speed is zero, and can display the echo. [0005] Such an underwater detection apparatus is also used in trawling ships. The trawling ships tow a trawling implement or trawling gear including an otter board (trawl door) and a net. Since the trawling implement is towed by the ship, the ground speed does not become zero and, thus, the trawling implement moves at substantially the same speed as the ship speed.

[0006] As for the zero ground-speed target object, such as the school of fish, can be detected by correcting the Doppler shift as described above, and the echo of the target object can be displayed. However, since the non-zero ground-speed trawling implement cannot be detected if the Doppler shift is corrected, the echo cannot be displayed. Therefore, when a user of the underwater detection apparatus performs trawling, he/she has to determine a capture of the school of fish only based on the indication of the echo of the detected school of fish in the state where the trawling implement is not detected. For this reason, it is desirable that both the school of fish and the trawling implement can be detected, and both the echoes can be displayed on the display unit.

Summary of the Invention

[0007] The purpose of the present disclosure relates to providing an underwater detection apparatus and an underwater detection method, which are capable of detecting both a school of fish and a trawling implement, and displaying both the echoes.

[0008] (1) An underwater detection apparatus according to one aspect of the present disclosure is an underwater detection apparatus to be used on a ship, which may include a transmission transducer, a reception transducer, a Doppler shift calculation module, a first signal processing module, a second signal processing module, and an image signal generation module. The transmission transducer may transmit an underwater transmission wave. The reception transducer may receive a reception wave comprising a reflection of the transmission wave on an underwater target and may generate a reception signal from the received reception wave. The Doppler shift calculation module may calculate a frequency shift amount by which a frequency of the reception wave is shifted relative to a frequency of the transmission wave. The first signal processing module may retrieve a first echo signal from the reception signal based on the frequency shift amount, the first echo signal being retrieved from the reception signal corresponding to the reception wave having an incoming azimuth angle from within a first direction range. The second signal processing module may retrieve a second echo signal from the reception signal independently of the frequency shift amount, the second echo signal being retrieved from the reception signal corresponding to the reception wave having an incoming azimuth angle from within a second direction range different from the first direction range. The image signal generation module may generate an echo image signal to display an echo of the target on a display unit based on the first echo signal and the second echo signal.

[0009] (2) The first direction range may include a heading direction of the ship and the second direction range may include a stern direction of the ship.

[0010] (3) When a heading direction of the ship changes, the second signal processing module may change the second direction range by changing a parameter that specifies the second direction range based on the heading direction change.

[0011] (4) When a heading direction of the ship changes, the second signal processing module may change the second direction range by changing a direction of a centre line that bisects the second direction range in two halves of equal range based on the heading direction change.

[0012] (5) When a heading direction of the ship changes clockwise, the second signal processing module may change the second direction range by changing counter clockwise a direction of a centre line that bisects the second direction range in two halves of equal range. [0013] (6) When a heading direction of the ship changes, the second signal processing module may change the second direction range by widening an angular range of the second direction range compared to when the heading direction of the ship does not change.

[0014] (7) An angular range of the first direction range may be wider than an angular range of the second direction range.

[0015] (8) The first signal processing module may retrieve the first echo signal by mixing the reception signal with a local signal having a frequency adjusted based on the frequency shift amount, or by filtering the reception signal, a frequency characteristic of the filtering being adjusted based on the frequency shift amount.

[0016] (9) The second signal processing module may retrieve the second echo signal by mixing the reception signal with a local signal having a fixed frequency set based on the frequency of the transmission wave, or by filtering the reception signal, a frequency characteristic of the filtering being adjusted based on the frequency of the transmission wave.

[0017] 00) The underwater detection apparatus may further include a data acquisition module configured to acquire at least one of a ship speed data of the ship and a warp length data of a warp connected between the ship and a trawl gear towed by the ship. The second signal processing module may retrieve the second echo signal by limiting a frequency band of the reception signal, the frequency band being adjusted based at least on one of the ship speed data and the warp length data.

[0018] (11) In a first situation in which the ship speed is faster than in a second situation, the frequency band may be narrower than in the second situation.

[0019] (12) In a third situation in which the warp length is shorter than in a fourth situation, the frequency band may be narrower than in the fourth situation.

[0020] (13) The image signal generation module may generate the echo image signal by allocating colours to the echo of the target corresponding to the first echo signal that are different from colours allocated to the echo of the target corresponding to the second echo signal.

[0021] (14) The second direction range may have an angular range that overlaps the first direction range.

[0022] (15) The underwater detection apparatus may further include a mark position setting module configured to set a position of an echo identified as an echo corresponding to at least a part of a trawl gear towed by the ship as a set mark position where a mark of the trawl gear is to be displayed. The image signal generation module may further generate a trawl mark image signal to display the mark or the trawl gear at the set mark position.

[0023] (16) When a heading direction of the ship changes, the mark position setting module may rotate the set mark position around a centre of rotation set at a position corresponding to a position of the ship.

[0024] (17) The second signal processing module may retrieve the second echo signal from the reception signal corresponding to the reception wave coming from within a given distance range from the reception transducer.

[0025] (18) The second signal processing module may retrieve the second echo signal from the reception signal corresponding to the reception wave coming from within a given underwater depth range.

[0026] (19) The first direction range may include the second direction range.

[0027] (20) Moreover, an underwater detection apparatus according to another aspect of the present disclosure is an underwater detection apparatus to be used on a ship for trawl fishing, which may include a transmission transducer, a reception transducer, a signal processing module, an image signal generation module, and a mark position setting module. The transmission transducer may transmit a transmission wave toward an underwater trawl gear. The reception transducer may receive a reception wave comprising a reflection of the transmission wave on the trawl gear and may generate a reception signal from the received reception wave. The signal processing module may retrieve an echo signal from the reception signal. The image signal generation module may generate an echo image signal based on the echo signal. The mark position setting module may set a position of an echo identified as an echo corresponding to at least a part of the trawl gear as a set mark position where a mark of the trawl gear is to be displayed. The image signal generation module may further generate a trawl mark image signal to display the mark of the trawl gear at the set mark position, and when a heading direction of the ship changes, the mark position setting module may rotate the set mark position around a centre of rotation set at a position corresponding to a position of the ship.

[0028] (21) Furthermore, an underwater detection apparatus according to still another aspect of the present disclosure is an underwater detection method. The method may include transmitting an underwater transmission wave, receiving a reception wave comprising a reflection of the transmission wave on an underwater target and generating a reception signal from the received reception wave, calculating a frequency shift amount by which a frequency of the reception wave is shifted relative to a frequency of the transmission wave, retrieving a first echo signal from the reception signal based on the frequency shift amount, the first echo signal being retrieved from the reception signal corresponding to the reception wave having an incoming azimuth angle from within a first direction range, retrieving a second echo signal from the reception signal independently of the frequency shift amount, the second echo signal being retrieved from the reception signal corresponding to the reception wave having an incoming azimuth angle from within a second direction range different from the first direction range, and generating an echo image signal to display an echo of the target on a display unit based on the first echo signal and the second echo signal.

Effect of the Invention [0029] According to the present disclosure, an underwater detection apparatus and an underwater detection method are provided, which are capable of detecting both a school of fish and a trawling implement, and displaying both the echoes.

Brief Description of Drawings

[0030] The present disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like reference numerals indicate like elements and in which: Fig. 1 is a block diagram illustrating a configuration of an underwater detection apparatus of a first embodiment; Fig. 2 is a view schematically illustrating a state of a ship trawling; Fig. 3 is a view schematically illustrating a transmission space where a transmission wave is transmitted from a transducer, and a reception space where a reception wave is received from the transducer; Fig. 4 is a block diagram illustrating a configuration of a signal processor of the underwater detection apparatus of the first embodiment; Fig. 5 is a view illustrating processing of a first signal processing module and a second signal processing module in the signal processor of the underwater detection apparatus of the first embodiment; Fig. 6 is a view illustrating processing of a second signal processing module in the signal processor of the underwater detection apparatus of the first embodiment; Fig. 7 is a view illustrating processing of the second signal processing module in the signal processor of the underwater detection apparatus of the first embodiment; Fig. 8 is a view illustrating processing of the second signal processing module in the signal processor of the underwater detection apparatus of the first embodiment; Fig. 9 is a view schematically illustrating one example of an image displayed on a display screen of a display unit; Fig. 10 is a flowchart illustrating operation of the underwater detection apparatus of the first embodiment; Fig. 11 is a view illustrating a first modification of the first embodiment, and is a view schematically illustrating one example of the image displayed in the display screen of the display unit; Fig. 12 is a view illustrating a second modification of the first embodiment, and is a view illustrating processing in the second modification of the first embodiment; Fig. 13 is a view illustrating the second modification of the first embodiment, and is a view schematically illustrating one example of the image displayed in the display screen of the display unit; Fig. 14 is a view illustrating a third modification of the first embodiment, and is a view illustrating processing in the third modification of the first embodiment; Fig. 15 is a view illustrating a comparative example of the third modification of the first embodiment, and is a view schematically illustrating one example of the image displayed in the display screen of the display unit; Fig. 16 is a view illustrating the third modification of the first embodiment, and is a view schematically illustrating one example of the image displayed in the display screen of the display unit; Fig. 17 is a view illustrating the third modification of the first embodiment, and is a view schematically illustrating one example of the image displayed in the display screen of the display unit; Fig. 18 is a view illustrating a fourth modification of the first embodiment, and is a view illustrating processing in the fourth modification of the first embodiment; Fig. 19 is a block diagram illustrating a configuration of a signal processor of the underwater detection apparatus of a second embodiment; Fig. 20 is a view schematically illustrating one example of the image displayed in the display screen of the display unit based on processing of the underwater detection apparatus of the second embodiment; Fig. 21 is a view schematically illustrating one example of the image displayed in the display screen of the display unit based on processing of the underwater detection apparatus of the second embodiment; Fig. 22 is an enlarged view illustrating a part of the example of the image illustrated in Fig. 21; Fig. 23 is a view illustrating processing of a mark position setting module in the signal processor of the underwater detection apparatus of the second embodiment; Fig. 24 is a view illustrating processing of the mark position setting module in the signal processor of the underwater detection apparatus of the second embodiment; and Fig. 25 is a view illustrating a modification of the second embodiment, and is a view illustrating processing in the modification of the second embodiment.

Detailed Description of the Invention

(First Embodiment) [0031] Hereinafter, an underwater detection apparatus 1 according to a first embodiment of the present disclosure is described with reference to the accompanying drawings.

[Entire Configuration of Underwater Detection Apparatus and Configuration of Trawling Implement] [0032] Fig. 1 is a block diagram illustrating a configuration of the underwater detection apparatus 1 according to the first embodiment of the present disclosure. The underwater detection apparatus 1 of this embodiment is, for example, used in a ship, such as a fishing boat, and, in more detail, is used in a trawling ship. Fig. 2 is a view schematically illustrating a state of the trawling ship S. The underwater detection apparatus 1 is used in the trawling ship S. [0033] As illustrated in Fig. 2, in trawling, a trawling implement (which may also be referred to as a trawl gear) 100 towed by the ship S is used. The trawling implement 100 may be comprised of otter boards 101 (which may also be referred to as "trawl doors") and a fishing net 102 for capturing a school of fish. The ship S and the trawling implement 100 towed by the ship S may be connected by warps 103.

[0034] The otter board 101 of the trawling implement 100 may be used in order to develop a net mouth 102a of the net 102. Note that, in Fig. 2, although a form in which one pair of otter boards 101 are provided is illustrated as the trawling implement 100, the configuration may be altered. For example, the trawling implement may be provided with three or more otter boards. For example, three otter boards of the trawling implement may develop the net mouths of two fishing nets.

[0035] The pair of otter boards 101 may he connected to the ship S through the respective warps 103. Each warp 103 may be sent out or wound up through the top rollers (not illustrated) provided at the stern or aft of the ship S. A warp length which is a length of the warp 103 connected to the trawling implement 100 and the ship S between the trawling implement 100 and the ship S may become longer as the warp 103 is sent out from the top roller, and become shorter as the warp 103 is wound up through the top roller. In more detail, the warp length may be defined as a length of the warp 103 between the otter board 101 and the top rollers provided at the stern of the ship S, and for example, may be measured based on the number of rotations of the top roller.

[0036] Each otter board 101 and the net 102 may be connected through a wire 104. A plurality of floats 105 may be provided to the net mouth 102a of the net 102. Note that the trawling implement 100 may be comprised of the otter boards 101 and the net 102. Alternatively, the trawling implement 100 may be comprised of the wires 104 and the floats 105, in addition to the otter boards 101 and the net 102.

[0037] The underwater detection apparatus 1 of the first embodiment used in the trawling ship S may he provided with a scanning sonar 10 and a signal processor 4, as illustrated in Fig. 1. The underwater detection apparatus 1 may have a configuration in which, for example, the signal processor 4 is externally connected to the generally-known scanning sonar 10. Alternatively, the underwater detection apparatus I may have a configuration in which the signal processor 4 is mounted on the scanning sonar 10, instead of being externally connected to the scanning sonar 10. Moreover, the underwater detection apparatus 1 may be externally connected to a display unit 5 constituted as a display device. In this example, the display unit 5 may be connected to the signal processor 4.

[0038] The scanning sonar 10 may include a transducer 2 (which may also be referred to as a transmission transducer and/or a reception transducer) and a transmitter/receiver 3.

[Configuration of Transducer] [0039] The transducer 2 may have a function to transmit and receive an ultrasonic wave, and may be attached to the bottom of the ship S. For example, the transducer 2 is formed in a substantially spherical shape.

[0040] In detail, the transducer 2 may have a substantially spherical casing and ultrasonic transducers (not illustrated) as a plurality of wave transmission/reception elements attached to an outer circumferential surface of this casing. The ultrasonic transducers may transmit the ultrasonic wave to an underwater transmission space as a transmission wave, receive a reception wave as a reflection wave containing a reflection of the transmission wave on an underwater target object, convert the reception wave into an electrical signal to generate a reception signal based on the reception wave, and output it to the transmitter/receiver 3. That is, the transducer 2 may be constituted as a transmitting transducer which transmits the transmission wave underwater, and may also be constituted as a receiving transducer which receives the reception wave containing the reflection of the transmission wave on the underwater target object and generates the reception signal based on the reception wave. The underwater target object at which the transmission wave transmitted from the transducer 2 reflects may include a school of fish and the trawling implement 100.

[0041] Note that, in this embodiment, although the casing of the transducer 2 is, but not limited to, spherical, or it may have other shapes, such as a substantially cylindrical shape. If the casing of the transducer 2 is substantially cylindrical, the transducer 2 may be oriented so that its axial direction is parallel to the vertical direction and its radial direction is parallel to the horizontal direction.

[0042] Fig. 3 is a view schematically illustrating a transmission space TS where the transmission wave is transmitted from the transducer 2, and a plurality of reception spaces RS where the reception wave is received from the transducer 2. The transmission waves transmitted from the transducer 2 mounted on the ship S may be transmitted underwater all at once toward all the directions centring on the ship S from the transducer 2, and for example, a hemispherical transmission beam is formed. When the hemispherical transmission beam is formed, the transmission space TS where the transmission wave may be transmitted is constituted as a hemispherical space. Note that the shape of the transmission beam is not limited to the hemispherical, but may he various different shapes according to the shape of the transducer 2, or amplitude and phase of an electrical signal which are inputted into each wave transmission/reception element of the transducer 2.

[0043] Moreover, the transducer 2 may then form, within the transmission space TS, a plurality of reception beams all at once to scan in the circumferential direction (in a direction of the azimuth angle 0 illustrated by an arrow in Fig. 3), after the transmission beam is transmitted. That is, all the reception beams may be formed at the single timing of the reception by the transducer 2. Then, the reception wave reflected at the underwater school of fish or the underwater target object of the trawling implement 100 may be received in each of the plurality of reception spaces RS (i.e., each space where the reception beam is formed) arranged in the circumferential direction of the transmission space TS (i.e., in the direction of the azimuth angle 0).

[Con figuration of Transmitter/Receiver] [0044] The transmitter/receiver 3 may include a transmission/reception switch 3a, a transmission circuit 6, and a reception circuit 7.

[0045] The transmission/reception switch 3a may switch the transducer 2 between transmission and reception of the signal. For example, when transmitting a drive signal for driving the transducer 2 to the transducer 2, the transmission/reception switch 3a outputs to the transducer 2 the drive signal outputted from the transmission circuit 6. On the other hand, when the reception signal is received from the transducer 2, the transmission/reception switch 3a may output to the reception circuit 7 the reception signal received from the transducer 2.

[0046] The transmission circuit 6 may generate the drive signal used as the basis of the transmission wave to be transmitted from the transducer 2. In more detail, the transmission circuit 6 may be comprised of a plurality of transmission circuit parts (not illustrated) provided corresponding to the respective ultrasonic transducers, and each transmission circuit may generate the drive signal.

[0047] The reception circuit 7 may have an analogue part 7a and an A/D conversion pan 7b. The analogue pan 7a and the A/D conversion part 7b may be comprised of a plurality of reception circuit parts (not illustrated) provided corresponding to the respective ultrasonic transducers, and each processes the reception signal generated from the received reception wave. Then, the analogue part 7a may amplify the reception signal as an electrical signal which is generated from the reception wave and outputted from the transducer 2, and remove an unnecessary frequency component by limiting the hand. The A/D conversion part 7b may convert the reception signal amplified by the analogue part 7a into a reception signal as a digital signal. Then, the reception circuit 7 may output the reception signal converted into the digital signal by the A/D conversion part 7b to the signal processor 4.

[Configuration of Display Unit] [0048] The display unit 5 may be constituted as a display device. The display unit 5 may display on a display screen an image according to an image signal outputted from the signal processor 4. For example, the display unit 5 displays an underwater state below the ship S as a three-dimensional bird's-eye view. Thus, a user of the underwater detection apparatus I may guess the underwater state below the ship S (e.g., the existence and the position of a school of fish, the trawling implement 100, and irregularity of the seabed, and a structure such as an artificial fish reet), by visually observing the display screen.

[Entire Configuration of Signal Processor] [0049] Fig. 4 is a block diagram illustrating a configuration of the signal processor 4. Referring to Figs. 1 and 4, the signal processor 4 may process the reception signal outputted from the reception circuit 7, generate an echo signal of a target object, and perform processing to generate an echo image signal for displaying the echo (signal) of the target object on the display unit 5.

[0050] The signal processor 4 may include a beam forming module 9, a data acquisition module 10, a Doppler shift calculation module 11, a first signal processing module 12, a second signal processing module 13, an image signal generation module 14, etc. [0051] The signal processor 4 may be an apparatus connected with the transmitter/receiver 3 of the scanning sonar 10 through a cable, and may be comprised of, for example, a personal computer (PC). The signal processor 4 may be comprised of devices, such as a hardware processor 8 (e.g., a CPU, a FPGA, etc.) and a nonvolatile memory. The hardware processor 8 may function as the beam forming module 9, the data acquisition module 10, the Doppler shift calculation module 11, the first signal processing module 12, the second signal processing module 13, and the image signal generation module 14, which will be described in detail below. For example, by the CPU reading a program from the nonvolatile memory and executing the program, the hardware processor 8 functions as the beam forming module 9, the data acquisition module 10, the Doppler shift calculation module 11, the first signal processing module 12, the second signal processing module 13, and the image signal generation module 14.

[Configuration of Beam Forming Module] [0052] The beam forming module 9 may perform beam forming processing (in detail, summing phase shifted signals) of each of the plurality of reception spaces RS based on the reception signal received from the reception circuit 7, and perform filter processing. Note that, in the beam forming processing, the beam forming module 9 may generate a reception beam signal which is a signal equivalent to what is obtained by a single ultrasonic transducer having a sharp directivity in a particular direction. The beam forming module 9 may generate a large number of reception beam signals having the directivity to respective directions corresponding to the respective reception spaces RS by repeating the beam forming processing while changing a combination of the ultrasonic transducer subjected to the beam forming processing. Further, the beam forming module 9 may perform the filter processing, such as a band-limiting filter or a pulse compression filter, to each reception beam formed corresponding to the reception space RS. By performing these processings, the beam forming module 9 may generate the reception signal to which the beam forming processing and the filter processing are performed.

[Configuration of Data Acquisition Module] [0053] The data acquisition module 10 may acquire data of a bow direction (which may also be referred to as heading direction) of the ship S, a traveling speed of the ship S (ship speed), and the warp length of the warps 103 connected between the ship S and the trawling implement 100 which is towed by the ship S. [0054] A gyrocompass (not illustrated) or a satellite compass (not illustrated) may be mounted on the ship S, which detects the bow direction of the ship S as an absolute direction. Note that the satellite compass has, for example, two GPS antennas attached to the ship S along a straight line parallel to the bow direction. The two GPS antennas may receive the radio waves transmitted from the positioning satellites, and the satellite compass may calculate a relative position between the two GPS antennas based on the career phases of the received radio wave signals to detect the bow direction of the ship S as the absolute direction. The gyrocompass or the satellite compass mounted on the ship S may be connected to the signal processor 4, and output the data of the detected bow direction to the signal processor 4.

[0055] Moreover, a ship speed meter (not illustrated) which measures the ship speed may be mounted on the ship S. For example, the ship speed meter is attached to the ship's bottom, and is constituted as a Doppler sonar which transmits an ultrasonic wave in a plurality of axial directions toward the seabed, and measures the Doppler frequencies contained in the reflection waves to obtain the ship speed. The ship speed meter mounted on the ship S may be connected to the signal processor 4, and output the data of the detected ship speed to the signal processor 4. Note that the ship S may not be provided with the ship speed meter as the independent apparatus, but the ship speed may he measured by the transducer 2.

[0056] A warp length measuring instrument (not illustrated) which measures the warp length may be, for example, comprised of an encoder that detects the number of rotations of the top rollers, which are provided at the stern of the ship S andwhich rotate when sending out and winding up the warps 103. The warp length measuring instrument may measure the warp length based on the number of rotations of the top rollers detected by the encoder. The warp length measuring instrument may be connected to the signal processor 4, and output the data of the measured warp length to the signal processor 4.

[0057] Note that, in this embodiment, although the data acquisition module 10 acquires both the data of the ship speed and the data of the warp length, the configuration may be altered. For example, the data acquisition module 10 may acquire at least one of the data of the ship speed and the data of the warp length.

[Configuration of Doppler Shift Calculation Module] [0058] When the reception wave is received from the transducer 2, the Doppler shift may occur, in which the frequency of the reception wave is shifted from the frequency of the transmission wave transmitted from the transducer 2 according to the ship speed and an incoming direction of the reception wave. The Doppler shift calculation module 1 I may calculate an amount of the frequency shift of the frequency of the reception wave from the frequency of the transmission wave.

[0059] The Doppler shift calculation module 11 may calculate the frequency shift amount for every reception space RS based on the data of the bow direction and the data of the ship speed which are acquired by the data acquisition module 10, and the reception signal which is generated by the beam forming module 9 and to which the beam forming processing and the filter processing are applied. In more detail, the Doppler shift calculation module 11 may calculate the frequency shift amount Af by using the following Formula (1) based on the ship speed v, a sound velocity c, a frequency f0 of the transmission wave, and an incoming azimuth angle Od of the reception wave from which the frequency shift amount Af is calculated.

Af = 2 x (v/c) x f0 x cosOd... (1) Note that, the incoming azimuth angle Od of the reception wave can be obtained as an angle formed by an azimuth direction of the target reception space RS for which the frequency shift amount Af is calculated, and the bow direction.

[Configuration of First Signal Processing Module and Second Signal Processing Module] [0060] The first signal processing module 12 may acquire or retrieve a first echo signal as an echo signal of the target object from the beam-formed reception signals based on the calculated frequency shift amount. In addition, the first signal processing module 12 may acquire or retrieve the first echo signal from the reception signal corresponding to the reception wave having the incoming azimuth angle within a given first direction range RI. That is, the first signal processing module 12 may correct, based on the calculated frequency shift amount, the reception signal corresponding to the reception wave which came from the first direction range RI to acquire the first echo signal as the echo signal of the target object which exists within the first direction range R I. In addition, the first signal processing module 12 may mix the beam-formed reception signal with a local signal having the frequency adjusted based on the frequency shift amount to acquire the first echo signal. Alternatively, the first signal processing module 12 may perform the filter processing to the beam-formed reception signal by the filter of which the frequency characteristic is adjusted based on the frequency shift amount to acquire the first echo signal.

[0061] The second signal processing module 13 may acquire or retrieve the second echo signal as the echo signal of the target object from the beam-formed reception signals, independently of the calculated frequency shift amount. In addition, the second signal processing module 13 may acquire or retrieve the second echo signal from the reception signal corresponding to the reception wave having an incoming azimuth angle from a given second direction range R2 different from the first direction range RI. That is, the second signal processing module 13 may acquire the second echo signal as the echo signal of the target object which exists within the second direction range R2 from the reception signal corresponding to the reception wave which came from the second direction range R2, without being based on the calculated frequency shift amount and therefore independently of the calculated frequency shift amount. In addition, the second signal processing module 13 may mix the beam-formed reception signal with a local signal having a fixed frequency set based on the frequency of the transmission wave to acquire the second echo signal. Alternatively, the second signal processing module 13 may perform the filter processing to the beam-formed reception signal by the filter of which the frequency characteristic is adjusted based on the frequency of the transmission wave to acquire the second echo signal. [0062] Fig. 5 is a view illustrating processing of the first signal processing module 12 and the second signal processing module 13 in the signal processor 4. In detail, Fig. 5 is a plan view schematically illustrating the ship S and its perimeter, schematically illustrating the first direction range RI and the second direction range R2 which are set by the processings of the first signal processing module 12 and the second signal processing module 13. Fig. 5 also schematically illustrates a detection area DR corresponding to the transmission space TS.

[0063] As illustrated in Fig. 5, the first signal processing module 12 may set the first direction range RI from which the first echo signal is acquired, as a direction range including a bow direction HD of the ship S. In addition, the first direction range RI is set, for example, as a direction range centring on the how direction HD. In more detail, the first direction range RI is set, for example, as a direction range of ±100° to ±170° centring on the bow direction HD. Note that the angular range of the first direction range RI may be set as an angular range wider than the angular range of the second direction range R2.

[0064] Then, the first signal processing module 12 may acquire the first echo signal from the reception signals generated in the respective plurality of reception beams formed within the first direction range RI set centring on the how direction HD. Thus, the first signal processing module 12 may acquire the first echo signal as the echo signal of the target object which exists within the first direction range RI, from the reception signal corresponding to the reception wave which came from the first direction range Rl. In addition, the first signal processing module 12 may correct the reception signal corresponding to the reception wave which came from the first direction range RI as described above based on the calculated frequency shift amount to acquire the first echo signal. Therefore, when the target object of the school of fish of which the ground speed is zero exists within the first direction range RI, the first signal processing module 12 may detect the target object of the school of fish and acquire the first echo signal as the echo signal of the target object of the school of fish.

[0065] Moreover, as illustrated in Fig. 5, the second signal processing module 13 may set the second direction range R2 from which the second echo signal is acquired, as a direction range including a stern direction TD of the ship S. In addition, the second direction range R2 is set, for example, as a direction range centring on the stern direction TD. In more detail, the second direction range R2 is set, for example, as a direction range of ±10° to ±80° centring on the stern direction TD. Note that, in this embodiment, the second direction range R2 may be set adjacent to the first direction range R I in the direction of the azimuth angle 0. That is, in this embodiment, boundary lines at both sides of the first direction range RI in the direction of the azimuth angle 0 and boundary lines at both sides of the second direction range R2 in the direction of the azimuth angle 0 may be located at the same locations. For example, the first direction range R1 is set as the direction range of ±140° centring on the how direction HD, and the second direction range R2 is set as the direction range of ±40° centring on the stern direction TD.

[0066] The second signal processing module 13 may acquire the second echo signal from the reception signals generated for the respective plurality of reception beams formed within the second direction range R2 which is set centring on the stern direction TD. Thus, the second signal processing module 13 may acquire the second echo signal as the echo signal of the target object which exists within the second direction range R2, from the reception signal corresponding to the reception wave which came from the second direction range R2. Moreover, the second signal processing module 13 may acquire the second echo signal from the reception signal corresponding to the reception wave which came from the second direction range R2, independently of the calculated frequency shift amount, as described above. Moreover, a target object as the trawling implement 100, which moves at substantially the same speed as the ship speed, may exist within the second direction range R2 which is a direction range on the stern direction TD side. Therefore, the second signal processing module 13 may detect the target object of the trawling implement 100 which exists within the second direction range R2, and acquire the second echo signal as the echo signal of the target object of the trawling implement 100.

[0067] In addition, when acquiring the second echo signal by performing the filter processing to the reception signal by the filter of which the frequency characteristic is adjusted based on the frequency of the transmission wave, the second signal processing module 13 may acquire the second echo signal by limiting the frequency band of the reception signal. Here, the second signal processing module 13 is configured, for example, so as to adjust the frequency band based on at least one of the data of the ship speed and the data of the warp length, which are acquired by the data acquisition module 10.

[0068] In more detail, when adjusting the frequency hand based on the data of the ship speed, the second signal processing module 13 may adjust to narrow the frequency band more in a first situation where the ship speed is faster than a given speed, than in a second situation where the ship speed is slower than the given speed. Therefore, when it is in the first situation where the ship speed is faster than the second situation, the frequency band may become narrower than that in the second situation. Moreover, when adjusting the frequency band based on the data of the warp length, the second signal processing module 13 may adjust to narrow the frequency band more in a third situation where the warp length is shorter than a given length, than in a fourth situation where the warp length is longer than the given length. Therefore, when it is in the third situation where the warp length is shorter than the fourth situation, the frequency band may become narrower than that in the fourth situation.

[0069] When the ship speed becomes faster and the warp length becomes shorter, a frequency variation of the reception signal corresponding to the reception wave reflected at the target object as the trawling implement 100 which exists within the second direction range R2 may become smaller. On the other hand, when the ship speed becomes slower and the warp length becomes longer, the frequency variation of the reception signal corresponding to the reception wave reflected at the target object as the trawling implement may become larger. Therefore, since the frequency hand is narrowed when the ship speed is faster than the given speed and the warp length is shorter than the given length, the frequency variation of the reception signal corresponding to the target object of the trawling implement 100 may become smaller, thereby acquiring the second echo signals for displaying the echoes of the trawling implement 100 on the display unit 5, of which contrast is raised. On the other hand, since the frequency band is broadened, rather than narrowed, when the ship speed is slower than the given speed and the warp length is longer than the given length, the omission in detection of the target object as the trawling implement 100 can be reduced even when the frequency variation of the reception signal corresponding to the target object of the trawling implement 100 is larger. Note that, although in this embodiment the second signal processing module 13 adjusts the frequency band based on at least one of the data of the ship speed and the data of the warp length, the adjustment may not be carried out.

[0070] Moreover, while the bow direction HD changes, the second signal processing module 13 may change the second direction range R2 by changing the parameter which defines or specifies the second direction range R2 based on the change in the bow direction HD. The parameter which defines the second direction range R2 and is changed when the bow direction HD changes may include various parameters, and may include, for example, a parameter of the direction of the centre line which angularly bisects the second direction range R2, or a parameter of the size of the angular range of the second direction range R2. When the bow direction HD changes, the second signal processing module 13 of this embodiment may change, for example, the parameter of the direction of the centre line which angularly bisects the second direction range R2.

[0071] Figs. 6 to 8 are views illustrating processing of the second signal processing module 13. Figs. 6 to 8 schematically illustrate the first direction range RI and the second direction range R2, along with the detection area DR corresponding to the transmission space TS. In more detail, Fig. 6 illustrates the first direction range RI and the second direction range R2 in a state where the bow direction HD does not change, and Figs. 7 and 8 illustrate the first direction range R I and the second direction range R2 in states where the bow direction HD changes. Note that, in Figs. 6 to 8, in order to illustrate a state of the change in the how direction HD, a trail WA of the ship S is also illustrated schematically.

[0072] As illustrated in Fig. 6, while the bow direction HD does not change the second signal processing module 13 may not change the direction of the centre line bisecting the second direction range R2. Note that, while the bow direction HD does not change, the direction of the centre line bisecting the second direction range R2 may become a direction parallel to the stern direction of the ship S. [0073] On the other hand, as illustrated in Figs. 7 and 8, while the bow direction HD changes, the second signal processing module 13 may change the second direction range R2 by changing the direction of a centre line CL bisecting the second direction range R2 based on the change in the how direction HD. Note that, in Figs. 7 and 8, the second direction range R2 when the bow direction HD changes is illustrated by a two-direction arrow R2 of a solid line, and boundary lines at both sides of the second direction range R2 when the bow direction HD changes is illustrated by broken lines. Moreover, in Figs. 7 and 8, the second direction range R2 before the change in the bow direction HD which is the state where the bow direction HD has not changed is illustrated by a two-direction arrow R20 of a two-dot chain line, the boundary lines at both sides of the second direction range R2 before the change in the bow direction HD are illustrated by two-dot chain lines, and the centre line of the second direction range R2 before the change in the bow direction HD is illustrated by a one-dot chain line CLO. As illustrated in Figs. 7 and 8, when the bow direction HD changes, the second signal processing module 13 may change the second direction range R2 by changing the direction of the centre line CL of the second direction range R2 based on the change in the bow direction HD.

[0074] Moreover, as illustrated in Fig. 7, while the bow direction HD changes clockwise, the second signal processing module 13 may change the second direction range R2 by changing the direction of the centre line CL of the second direction range R2 counterclockwise. On the other hand, as illustrated in Fig. 8, while the bow direction HD changes counterclockwise, the second signal processing module 13 changes the second direction range R2 by changing the direction of the centre line CL of the second direction range R2 clockwise. Note that, when the second signal processing module 13 changes the second direction range R2 while the bow direction HD changes, the first signal processing module 12 may change the first direction range R1 so that the first direction range R1 is always adjacent to the second direction range R2 in the direction of the azimuth angle 0, according to the changed second direction range R2.

[0075] As described above, while the bow direction HD changes, the second signal processing module 13 may change the second direction range R2 by changing the parameter which defines the second direction range R2, based on the change in the bow direction HD. Therefore, the second direction range R2 can be changed so that the trawling implement 100 of which the relative position to the ship S changes when the bow direction HD changes exists within the second direction range R2.

[0076] Note that, after the change in the bow direction HD is finished, the second signal processing module 13 may change the second direction range R2 so that the direction of the centre line CL of the second direction range R2 becomes again parallel to the stern direction TD (see Fig. 6). That is, when the bow direction HD resumes the state where it does not change, the second signal processing module 13 may change the second direction range R2 so that direction of the centre line CL of the second direction range R2 is returned into the direction parallel to the stern direction TD.

[Configuration of Image Signal Generation Module] [0077] The image signal generation module 14 may generate the echo image signals for displaying the echoes of the target objects on the display unit 5 based on the first echo signal and the second echo signal which are generated by the first signal processing module 12 and the second signal processing module 13. In addition, the image signal generation module 14 may also generate the echo image signal for displaying the respective target objects corresponding to the first echo signal and the second echo signal as a three-dimensional area image, for example, by performing isosurface processing (i.e., surface rendering processing) or volume rendering processing. Note that the three-dimensional area image may be an image expressing a distribution of the target objects in the three-dimensional area. The echo image signal generated by the image signal generation module 14 may be outputted to the display unit 5, and the echoes of the target objects may be displayed in the display screen of the display unit 5. Fig. 9 is a view schematically illustrating one example of an image displayed in the display screen of the display unit 5. Note that, in Fig. 9, a three-dimensional area image IM1 which is displayed in the display screen of the display unit 5 based on the echo image signal generated by the image signal generation module 14 is illustrated.

[0078] As illustrated in Fig. 9, in the three-dimensional area image IM1 displayed on the display unit 5, echoes (El, E2, E3, E4, ES, and E6) of the target objects detected in the underwater detection area DR corresponding to the transmission space TS may be displayed. Note that the three-dimensional area image IM1 may be displayed in a state where it is projected onto a two-dimensional display screen of the display unit 5. Moreover, the indication of the three-dimensional area image IM1 may also include indications of the distance lines HL1 and HL2 indicative of equidistant positions from the ship S on the water surface, and indications of depth lines VL1 and VL2 indicative of equidepth positions in the water depth direction. Note that, in Fig. 9, although a line indicative of the detection area DR is displayed in the three-dimensional area image IM1, it may not be displayed.

[0079] The image signal generation module 14 may generate the echo image signals for displaying the echoes (El, E2, and E3) of the target objects on the display unit 5 based on the first echo signals generated by the first signal processing module 12. The echoes (El, E2, and E3) may be each displayed based on the echo image signal which is generated from the first echo signal that is the echo signal of the target object as a school of fish which exists in the first direction range RI and of which the ground speed is zero. Therefore, the echoes (El, E2, and E3) may indicate the echoes of the target objects as schools of fish.

[0080] The image signal generation module 14 may also generate the echo image signals for displaying the echoes (E4, E5, and E6) of the target objects on the display unit 5 based on the second echo signals generated by the second signal processing module 13. The echoes (E4, E5, and E6) may he each displayed based on the echo image signal generated from the second echo signal that is the echo signal of the target object as the trawling implement 100 which exists within the second direction range R2 and moves at substantially the same speed as the ship S. Therefore, the echoes (E4, E5, and E6) may indicate the echoes of the target object as the trawling implement 100. Note that, in Fig. 9, as the echoes (E4, E5, and E6) of the trawling implement 100, the echoes (E4 and E5) of the target objects of the otter boards 101 and the echo E6 of the wires 104 and the floats 105 near the net mouth 102a of the net 102 are displayed.

[0081] Note that, in the three-dimensional area image IM1 illustrated in Fig. 9, an area corresponding to the echo signal at a high signal intensity level is indicated by a high-density dot hatching area, an area corresponding to the echo signal at a moderate signal intensity is indicated by an oblique hatching area, and an area corresponding to the echo signal at a low signal intensity level is indicated by a low-density dot hatching area. The echo image signal generated by the image signal generation module 14 may include information on display colours of the signal intensity level when displayed on the display unit 5. Therefore, on the display unit 5, the high echo intensity area, the moderate echo intensity area, and the low echo intensity area may be each displayed in a colour based on the display colour information contained in the echo image signal. For example, the high echo intensity area is displayed in red, the moderate echo intensity area is displayed in green, and the low echo intensity area is displayed in blue.

[Operation of Underwater Detection Apparatus] [0082] Fig. 10 is a flowchart illustrating one example of operation of the underwater detection apparatus 1. In Fig. 10, this operation includes transmitting the transmission wave underwater from the transducer 2, receiving the reception wave including the reflection of the transmission wave by the transducer 2, performing the processing by the underwater detection apparatus I as described above, and displaying the echo images of the target object on the display unit 5. After the echo images of the target object are displayed on the display unit 5, the operation illustrated in the flowchart of Fig. 10 may be again performed when the transmission wave is transmitted underwater from the transducer 2. Note that, as illustrated in Fig. 10, the underwater detection method of this embodiment may be implemented by performing the operation of the underwater detection apparatus 1.

[0083] In the operation of the underwater detection apparatus 1, first, the transmission wave may be first transmitted underwater to the transmission space TS from the transducer 2. The transmission wave transmitted underwater to the transmission space TS may be reflected at an underwater target object and received from the transducer 2. The transducer 2 may receive the reception wave including the reflection of the transmission wave on the underwater target object, and then generate the reception signal from the received reception wave (Step S101). The transducer 2 may output the generated reception signal to the transmitter/receiver 3. In the transmitter/receiver 3, the reception circuit 7 may amplify the received reception signal, remove the unnecessary frequency component, convert the signal into the digital signal, and then output the reception signal to the signal processor 4.

[0084] In the signal processor 4, the beam forming module 9 may perform the beam forming processing, when the reception signal is inputted from the transmitter/receiver 3 (Step S102). That is, the beam forming module 9 may generate a large number of reception beam signals having the directivities in the respective azimuth directions corresponding to the respective reception spaces RS by performing the beam forming processing of the respective plurality of reception spaces RS based on the reception signals. When the beam forming module 9 finishes the beam forming processing, the Doppler shift calculation module 11 may then calculate the amount of the frequency shift caused to the frequency of the reception wave shifted from the frequency of the transmission wave, according to the incoming azimuth angle of the reception wave (Step S103).

[0085] The first signal processing module 12 may then acquire the first echo signal from the reception signal based on the frequency shift amount (Step S104). At this time, the first signal processing module 12 may acquire the first echo signal from the reception signal corresponding to the reception wave having the incoming azimuth angle from the first direction range R 1. Then, the second signal processing module 13 may acquire the second echo signal from the reception signals, independently of the frequency shift amount (Step S105). At this time, the second signal processing module 13 may acquire the second echo signal from the reception signal corresponding to the reception wave having the incoming azimuth angle from the second direction range R2 different from the first direction range RI. [0086] When the first signal processing module 12 and the second signal processing module 13 acquire the first echo signal and the second echo signal, the image signal generation module 14 may then generate the echo image signals for displaying the echoes of the target objects on the display unit 5 based on the first echo signal and the second echo signal (Step SI06). Then, the generated echo image signal may be outputted to the display unit 5 (Step S107). The display unit 5 may display the echo images of the target object based on the inputted echo image signal, as illustrated in Fig. 9. Therefore, on the display unit 5, the echoes (El, E2, and E3) of the target objects as schools of fish detected in the first direction range RI and the echoes (E4, ES, and E6) of the target objects as the trawling implement 100 detected in the second direction range R2 may be displayed. When the echo of the target object is displayed on the display unit 5, the operation illustrated in Fig. 10 of the underwater detection apparatus I may once be finished. After the operation illustrated in Fig. 10 is finished, the transmission wave may be transmitted underwater to the transmission space TS from the transducer 2, and the operation illustrated in Fig. 10 may then be started again.

[Effects] [0087] According to this embodiment, the first echo signal may he acquired from the reception signal corresponding to the reception wave having the incoming azimuth angle from the first direction range RI based on the frequency shift amount. Therefore, when the target object of the school of fish of which the ground speed is zero exists within the first direction range RI, the target object of the school of fish may he detected and the first echo signal as the echo signal of the target object of the school of fish may be acquired. Further, according to this embodiment, independently of the frequency shift amount, the second echo signal may be acquired from the reception signal corresponding to the reception wave having the incoming azimuth angle from the second direction range R2 different from the first direction range Rl. Therefore, the target object of the trawling implement 100 which exists within the second direction range R2 may be detected, and the second echo signal as the echo signal of the target object of the trawling implement 100 may be acquired. Then, according to this embodiment, based on the first echo signal corresponding to the echo of a school of fish, and the second echo signal corresponding to the trawling implement 100, the echo image signals for displaying the echoes of the target objects of the school of fish and the trawling implement 100 on the display unit 5 may he generated, and the echoes of the school of fish and the trawling implement 100 may be displayed on the display unit 5 based on the echo image signals.

[0088] Therefore, according to this embodiment, the underwater detection apparatus and the underwater detection method, which can detect both the school of fish and the trawling implement and display both the echoes, can be provided.

[0089] Moreover, according to this embodiment, the first direction range RI may include the bow direction of the ship S, and the second direction range R2 may include the stern direction of the ship S. Therefore, the school of fish which exists in the traveling direction of the trawling ship S can be detected more securely, and the trawling implement 100 which exists in the stern direction of the ship S can also be detected more securely.

[0090] Moreover, according to this embodiment, while the bow direction HD changes, the second signal processing module 13 may change the parameter which defines the second direction range R2 based on the change in the how direction HD to change the second direction range R2. Therefore, the second direction range R2 can be changed so that the trawling implement 100 of which the relative position to the ship S changes when the bow direction HD changes exists within the second direction range R2.

[0091] Moreover, according to this embodiment, while the bow direction HD changes, the second signal processing module 13 may change the direction of the centre line bisecting the second direction range R2 based on the change in the how direction HD to change the second direction range R2. Therefore, when the bow direction HD changes, the direction of the centre line of the second direction range R2 can be easily turned into the area where the trawling implement 100 exists with a high possibility. Therefore, the second direction range R2 can be changed so that the trawling implement 100 exists stably in the second direction range R2.

[0092] Moreover, according to this embodiment, the second signal processing module 13 may change the second direction range R2 by changing the direction of the centre line of the second direction range R2 counterclockwise when the direction of the how direction HD is changed clockwise, and changing the direction of the centre line of the second direction range R2 clockwise when the direction of the bow direction HD is changed counterclockwise. Therefore, the direction of the centre line of the second direction range R2 can he easily turned into the area where the trawling implement 100 exists with a high possibility, according to the change in the direction of the bow direction HD. Therefore, the second direction range R2 can be changed so that the trawling implement 100 exists stably in the second direction range R2.

[0093] Moreover, according to this embodiment, the angular range of the first direction range RI may be set wider than the angular range of the second direction range R2. Therefore, the second direction range can be set according to the area where the trawling implement 100 exists, and the first direction range RI can be set so that a school of fish is detected in a larger area.

[0094] Moreover, according to this embodiment, the second signal processing module 13 may adjust the frequency hand of the reception signal based on the data of the ship speed and the data of the warp length. Then, the second signal processing module 13 may adjust the frequency band so that the frequency band is narrowed in the first situation where the ship speed is faster than the given speed more than that of the second situation where the ship speed is slower than the given speed. That is, the frequency band in the first situation where the ship speed is faster than the second situation may he narrower than the second situation. Further, the second signal processing module 13 may adjust the frequency band so that the frequency band is narrowed in the third situation where the warp length is shorter than the given length more than that of the fourth situation where the warp length is longer than the given length. That is, the frequency band in the third situation where the warp length is shorter than the fourth situation may be narrower than the fourth situation. Therefore, since the frequency band is narrowed when the ship speed is faster than the given speed and the warp length is shorter than the given length, the second echo signal for displaying on the display unit 5 the echoes of the trawling implement 100 of which the contrast is raised can be acquired when the frequency variation of the reception signal corresponding to the target object of the trawling implement 100 is small. On the other hand, since the frequency band is broadened without being narrowed when the ship speed is slower than the given speed and the warp length is longer than the given length, the omission in the detection of the target object as the trawling implement 100 can be reduced when the frequency variation of the reception signal corresponding to the target object of the trawling implement 100 is large.

(First Modification of First Embodiment) 100951 Fig. 11 is a view illustrating a first modification of the first embodiment, where one example of the image displayed in the display screen of the display unit 5 is schematically illustrated. Note that, in the following description, differences from the first embodiment will be described and the same or corresponding configurations are assigned with the same reference characters in the drawing or refer the same reference characters to suitably omit redundant description.

[0096] In the first embodiment, the echoes (El, E2, and E3) of the target objects generated based on the first echo signals and the echoes (E4, ES, and E6) of the target objects generated based on the second echo signals may be displayed similarly in the display colour according to the signal intensity levels. On the other hand, in the first modification of the first embodiment, the echoes (El, E2, and E3) of the target objects displayed based on the echo image signals generated from the first echo signals, and the echoes (E4, ES, and E6) of the target objects displayed based on the echo image signals generated from the second echo signals may be displayed differently in the display colour.

[0097] For example, in the first modification of the first embodiment, the image signal generation module 14 assigns a different colour from the colour assigned to the echoes (El, E2, and E3) of the target objects corresponding to the first echo signal, to the echoes (E4, E5, and E6) of the target objects corresponding to the second echo signal, to generates the echo image signal. That is, the echo image signals corresponding to the first echo signals for displaying the echoes (El, E2, and E3) and the echo image signals corresponding to the second echo signals for displaying the echoes (E4, E5, and E6) may include information on different colours as the information on the display colour to be displayed on the display unit 5. Then, on the display unit 5, the echo images may be displayed in the colours based on the information on the display colour contained in the echo image signal.

[0098] Note that, in the displayed example of the display screen of the display unit 5 illustrated in Fig. 11, the echoes (El, E2, and E3) corresponding to the first echo signals may be indicated by a high-density dot-hatching area, an oblique-hatching area, and a low-density dot-hatching area, and the echoes (E4, E5, and E6) corresponding to the second echo signals may be indicated by half-tone dot meshing areas. For example, on the display unit 5, the background colour of the display screen is black, the high-density dot-hatching area is indicated in red, the oblique-hatching area is in green, the low-density dot-hatching area is in blue, and the half-tone dot meshing area is in white.

[0099] According to the first modification of the first embodiment, the echoes (El, E2, and E3) of the target objects generated based on the first echo signals and the echoes (E4, E5, and E6) of the target objects generated based on the second echo signals can be displayed differently in the display colour. Therefore, the user can visually recognize more easily the echo of a school of fish and the echoes of the trawling implement 100.

(Second Modification of First Embodiment) [0100] Fig. 12 is a view illustrating a second modification of the first embodiment, where processing in the second modification of the first embodiment is illustrated. Note that, in the following description, differences from the first embodiment will be described, and the same or corresponding configurations may be assigned with the same reference characters in the drawing or refer the same reference characters to suitably omit redundant description. [0101] Fig. 12 is a view illustrating processing of the first signal processing module 12 in the second modification of the first embodiment. Moreover, Fig. 12 is a plan view schematically illustrating the ship S and its perimeter, and schematically illustrates the first direction range R1 and the second direction range R2 which are set by the processings of the first signal processing module 12 and the second signal processing module 13.

[0102] As illustrated in Fig. 12, in the second modification of the first embodiment, the first signal processing module 12 may set the first direction range R1 from which the first echo signal is acquired as a direction range including the bow direction HD of the ship S, and also may set it as a direction range of ±180° centring on the bow direction HD. That is, in the second modification of the first embodiment, the first signal processing module 12 may set the first direction range RI from which the first echo signal is acquired as a direction range covering all directions of the azimuth angle 0. Therefore, the second direction range R2 set by the second signal processing module 13 as the direction range including the stern direction TD of the ship S may have a direction range which overlaps with the first direction range RI, and in this modification, the second direction range R2 may be entirely included in the first direction range RI.

[0103] In the second modification of the first embodiment, since the first direction range RI is set as described above, the first echo signal may be acquired from the reception signal corresponding to the reception wave which comes from the direction range covering all directions of the azimuth angle 0. Therefore, the target object of a school of fish of which the ground speed is zero may be detected in the direction range covering all the directions of the azimuth angle 0. On the other hand, since the second direction range R2 is set similarly to the first embodiment, the second echo signal corresponding to the trawling implement 100 may be acquired from the reception signal corresponding to the reception wave which comes from the second direction range R2 including the stern direction TD.

[0104] Fig. 13 is a view illustrating the second modification of the first embodiment, where one example of the image displayed in the display screen of the display unit 5 is schematically illustrated. In the displayed example of the display screen of the display unit 5 illustrated in Fig. 13, echoes (El, E2, E3, and E7) may be displayed as the echoes of the target objects corresponding to the first echo signals, and echoes (E4, ES, and E6) may be displayed as the echoes of the target objects corresponding to the second echo signals. In the second modification of the first embodiment, the image signal generation module 14 may assign to the echoes (E4, ES, and E6) of the target objects corresponding to the second echo signals different colours from colours assigned to the echoes (El, E2, E3, and E7) of the target objects corresponding to the first echo signals, similar to the first modification of the first embodiment, to generate the echo image signal. That is, the echo image signals corresponding to the first echo signals for displaying the echoes (El, E2, E3, and E7) and the echo image signals corresponding to the second echo signals for displaying the echoes (E4, ES, and E6) may include information on different colours as the information on the display colours to be displayed on the display unit 5. Then, on the display unit 5, the echo images may he displayed by the colours based on the information on the display colours included in the echo image signals.

[0105] Note that, in the displayed example of the display screen of the display unit 5 illustrated in Fig. 13, the echoes (El, E2, E3, and E7) corresponding to the first echo signals may be indicated by a high-density dot-hatching area, an oblique-hatching area, and a low-density dot-hatching area, and the echoes (E4, E5, and E6) corresponding to the second echo signals may be indicated by a half-tone dot meshing area. For example, on the display unit 5, the background colour of the display screen is black, the high-density dot-hatching area is indicated in red, the oblique-hatching area is in green, the low-density dot-hatching area is in blue, and the half-tone dot meshing area is in white.

[0106] According to the second modification of the first embodiment, since the first direction range R I and the second direction range R2 have the overlapping direction range, the school of fish can be detected also in the area for detecting the trawling implement 100. That is, the trawling implement 100 and the school of fish can be detected simultaneously in the same direction range.

[0107] Moreover, according to the second modification of the first embodiment, even if the first direction range RI and the second direction range R2 are overlapped with each other, the echoes (El, E2, E3, and E7) of the target objects generated based on the first echo signals and the echoes (E4, ES, and E6) of the target objects generated based on the second echo signals can be displayed differently in the display colour. Therefore, even if the first direction range R I and the second direction range R2 are overlapped with each other, the user can visually recognize easily the echo of the school of fish and the echoes of the trawling implement 100.

(Third Modification of First Embodiment) [0108] Fig. 14 is a view illustrating a third modification of the first embodiment, where processing in the third modification of the first embodiment is illustrated. Note that, in the following description, differences from the first embodiment will be described, and the same or corresponding configurations may be assigned with the same reference characters in the drawing or refer the same reference characters to suitably omit redundant description. [0109] Fig. 14 is a view illustrating processings of the first signal processing module 12 and the second signal processing module 13 in the third modification of the first embodiment. Moreover, Fig. 14 is a plan view schematically illustrating the ship S and its perimeter, and schematically illustrates the first direction range RI and the second direction range R2 set by the processings of the first signal processing module 12 and the second signal processing module 13, and a second echo signal acquisition area RX which is a range where the second echo signal is acquired.

[0110] As illustrated in Fig. 14, in the third modification of the first embodiment, the first signal processing module 12 may set the first direction range RI from which the first echo signal is acquired as a direction range including the bow direction HD, and as a direction range of ±180° centring on the bow direction HD. That is, in the third modification of the first embodiment, the first signal processing module 12 may set the first direction range R1 from which the first echo signal is acquired as a direction range covering all directions of the azimuth angle 0. Therefore, the second direction range R2 set as the direction range including the stern direction TD of the ship S by the second signal processing module 13 may have a direction range which overlaps with the first direction range Rl. In this modification, the first direction range R I may include the second direction range R2, and include the entire second direction range R2.

[0111] In the third modification of the first embodiment, the first direction range RI may be set as described above. Thus, the first signal processing module 12 may acquire the first echo signal from the reception signal corresponding to the reception wave which comes from the direction range covering all directions of the azimuth angle 0. Therefore, the target object of the school of fish of which the ground speed is zero can be detected in the direction range covering all directions of the azimuth angle 0.

[0112] Moreover, the second direction range R2 may be set similarly to the first embodiment. However, in the third modification of the first embodiment, the second signal processing module 13 may acquire the second echo signal corresponding to the trawling implement 100 from the reception signal corresponding to the reception wave which comes from the second echo signal acquisition area RX which is a more limited area in the second direction range R2. The second echo signal acquisition area RX may be an area in the second direction range R2, and may be an area within a given distance range DX apart from the transducer 2 as the receiving transducer. The given distance range DX apart from the transducer 2 may be a distance range from the transducer 2, which is more than a given minimum distance DI and less than a given maximum distance D2. Note that, in Fig. 14, the positions of the minimum distance Dl and the maximum distance D2 from the transducer 2 may be illustrated by broken lines. Therefore, in the plan view schematically illustrated in Fig. 14, the second echo signal acquisition area RX may be an area surrounded by the broken line indicative of the minimum distance Dl, the broken line indicative of the maximum distance D2, and the broken lines indicative of the boundary lines at both sides of the second direction range R2.

[0113] As described above, in the third modification of the first embodiment, the second signal processing module 13 may acquire the second echo signal from the reception signal corresponding to the reception wave which comes from the second echo signal acquisition area RX. That is, the second signal processing module 13 may acquire the second echo sign& from the reception signal corresponding to the reception wave having the incoming azimuth angle from the second direction range R2, and from the reception signal corresponding to the reception wave which comes from the given distance range DX apart from the transducer 2 as the receiving transducer.

[0114] Note that the given distance range DX which defines the second echo signal acquisition area RX may be set beforehand, or may be set based on operation by the user of the underwater detection apparatus 1. If setting the range based on the operation by the user of the underwater detection apparatus 1, for example, the user suitably operates a user interface (not illustrated) provided to the underwater detection apparatus 1, such as a keyboard or a pointing device to set the minimum distance DI and the maximum distance D2, thereby, setting the given distance range DX. Alternatively, by the operation of the user, a centre value of the distance and a width of the distance which define the given distance range DX may be set, thereby, setting the given distance range DX. In this case, the centre value of the distance is, for example, set as an average value of the minimum distance DI and the maximum distance D2 (i.e., a value acquired by dividing the sum of the minimum distance Dl and the maximum distance D2 by 2). Further, the width of the distance is set, for example, as a value of a difference between the maximum distance D2 and the minimum distance DI. Alternatively, only the width of the distance may be set by the operation of the user among the centre value of the distance and the width of the distance which define the given distance range DX, and the centre value of the distance may he set based on the data of the warp length. In this case, the centre value of the distance may be set, for example, as a value of a given multiple of the warp length based on the data of the warp length acquired by the data acquisition module 10.

[0115] Fig. 15 is a view illustrating a comparative example of the third modification of the first embodiment, where one example of the image displayed in the display screen of the display unit 5 is illustrated. Fig. 16 is a view illustrating the third modification of the first embodiment, where one example of the image displayed in the display screen of the display unit 5 is schematically illustrated. In Figs. 15 and 16, as the three-dimensional area image displayed on the display unit 5 based on the echo image signals generated by the image signal generation module 14, a three-dimensional area image IM2 viewed from the above of the ship S may be displayed on the display unit 5. The three-dimensional area image 1M2 may be displayed as an image viewed from a vertical viewpoint which is a viewpoint from which the detection area DR is viewed in the vertical direction from the above of the ship S. [01 I 6] In the displayed example as the comparative example of the third modification of the first embodiment illustrated in Fig. 15, regarding an area other than the second direction range R2 in the first direction range RI, the echoes (El, E2, and E3) may be displayed as echoes of the target objects corresponding to the first echo signals, and regarding the area of the second direction range R2, the echoes (E4 and ES) are displayed as echoes of the target objects corresponding to the second echo signals. Therefore, in this comparative example, the user can visually observe the echoes of schools of fish in an area of the first direction range RI other than the second direction range R2, and can visually observe the echoes of the trawling implement 100 in the area of the second direction range R2. However, in this comparative example, the user cannot visually observe the echo of a school of fish in the area of the second direction range R2.

[0117] On the other hand, in the displayed example of the third modification of the first embodiment illustrated in Fig. 16, the echoes (El, E2, E3, E7, and E8) may be displayed as echoes of the target objects corresponding to the first echo signals, and the echoes (E4 and E5) are displayed as echoes of the target objects corresponding to the second echo signals. In the third modification of the first embodiment, the image signal generation module 14 may generate the echo image signals for displaying the echoes of the target objects on the display unit 5 based on the first echo signal, for the area other than the second echo signal acquisition area RX in the area of the first direction range R1 including the second direction range R2. Further, the image signal generation module 14 may generate the echo image signals for displaying the echoes of the target objects on the display unit 5 based on the second echo signal, for the second echo signal acquisition area RX in the second direction range R2. On the display unit 5, the echo images may be displayed based on the echo image signal generated by the image signal generation module 14. Therefore, as illustrated in Fig. 16, in the third modification of the first embodiment, the echoes (E4 and ES) of the trawling implement 100 may be displayed in the second echo signal acquisition area RX in the display screen of the display unit 5. In the area other than the second echo signal acquisition area RX, the echoes (El, E2, E3, E7, and E8) of schools of fish may be displayed. Therefore, in the third modification of the first embodiment, in the area of the second direction range R2, the echoes (E4 and E5) of the trawling implement 100 may be displayed in the second echo signal acquisition area RX, and the echoes (E7 and E8) of schools of fish may be displayed in an area other than the second echo signal acquisition area RX. Note that, in the displayed example illustrated in Fig. 16, the echoes (El, E2, E3, E7, and E8) of the target objects generated based on the first echo signal, and the echoes (E4 and ES) of the target objects generated based on the second echo signal may be displayed similarly in the display colour according to the signal intensity level.

[01181 According to the third modification of the first embodiment, the echoes (E4 and E5) of the trawling implement 100 may be displayed in the narrow area which is only the second echo signal acquisition area RX. That is, the echoes (E4 and E5) of the trawling implement 100 may be displayed only in the second echo signal acquisition area RX which is obtained by further limiting the second direction range R2 to the given distance range DX. On the other hand, the echoes (El, E2, E3, E7, and E8) of schools of fish may be also displayed in an area other than the second echo signal acquisition area RX in the second direction range R2, in addition to an area other than the second direction range R2 in the first direction range R I. Therefore, according to the third modification of the first embodiment, the area where the echoes of the trawling implement 100 is displayed may be limited to the narrower area around the trawling implement 100, and the echoes of schools of fish can be displayed in a larger area. Moreover, the area where the echoes of the trawling implement 100 are displayed, and the area where the echoes of schools of fish may be displayed are distinguished by the second echo signal acquisition area RX and the area other than the second echo signal acquisition area RX. Therefore, the echoes of the trawling implement 100 and the echoes of schools of fish can be displayed similarly in the display colour, thereby reducing time and effort for the setting of the display colours.

[0119] Moreover, in the third modification of the first embodiment, as a display mode of the image in the display screen of the display unit 5, other display modes may also be adopted in addition to the display mode illustrated in Fig. 16. Fig. 17 is a view illustrating a third modification of the first embodiment, where one example of the image displayed in the display screen of the display unit 5 is schematically illustrated. Fig. 17 illustrates a different displayed example from Fig. 16. In Fig. 17, as the three-dimensional area image displayed on the display unit 5 based on the echo image signal generated by the image signal generation module 14, the three-dimensional area image 1M2 may be displayed on the display unit 5, which views the detection area DR in the vertical viewpoint from above of the ship S, similar to the displayed example of Fig. 16.

[0120] In the displayed example of the third modification of the first embodiment illustrated in Fig. 17, echoes (El, E2, E3, E7, E8, and E9) may be displayed as echoes of the target objects corresponding to the first echo signals, and echoes (E4 and ES) are displayed as echoes of the target objects corresponding to the second echo signals. In the third modification of the first embodiment which illustrates the displayed example in Fig. 17, the image signal generation module 14 may generate the echo image signals for displaying the echoes of the target objects on the display unit 5 based on the first echo signals for the area of the first direction range RI including the second direction range R2. Further, the image signal generation module 14 may generate the echo image signals for displaying the echoes of the target objects on the display unit 5 based on the second echo signals for the second echo signal acquisition area RX in the second direction range R2.

[0121] Moreover, the image signal generation module 14 may assign different colours from the colours assigned to the echoes (El, E2, E3, E7, E8, and E9) of the target objects corresponding to the first echo signals to the echoes (E4 and E5) of the target objects corresponding to the second echo signals to generate the echo image signal. That is, the echo image signals corresponding to the first echo signals for displaying the echoes (El, E2, E3, E7, E8, and E9), and the echo image signals corresponding to the second echo signals for displaying the echoes (E4 and E5) may contain the information on different colours as the information on the display colour to he displayed on the display unit 5. On the display unit 5, the echo images may be displayed in the colours based on the information on the display colour contained in the echo image signal.

[0122] Note that, in the displayed example of the display screen of the display unit 5 illustrated in Fig. 17, the echoes (El, E2, E3, E7, E8, and E9) corresponding to the first echo signals may be indicated by the high-density dot-hatching area, the oblique-hatching area, and the low-density dot-hatching area, and the echoes (E4 and E5) corresponding to the second echo signals are indicated by the half-tone dot meshing areas. For example, on the display unit 5, the background colour of the display screen is black, the high-density dot-hatching area is indicated in red, the oblique-hatching area is in green, the low-density dot-hatching area is in blue, and the half-tone dot meshing area is in white.

[0123] In the displayed example illustrated in Fig. 17 of the third modification of the first embodiment, the echo images may be displayed on the display unit 5 based on the echo image signals generated as described above by the image signal generation module 14. Therefore, as illustrated in Fig. 17, in the display screen of the display unit 5, the echoes (El, E2, E3, E7, E8, and E9) of schools of fish may be displayed in the entire area of the first direction range R1 including the second direction range R2. In the second echo signal acquisition area RX, the echoes (E4 and ES) of the trawling implement 100 may be displayed in the different display colours from the display colours of the echoes (E 1, E2, E3, E7, ES, and E9) of schools of fish. Thus, in the displayed example illustrated in Fig. 17 of the third modification of the first embodiment, in the second echo signal acquisition area RX within the second direction range R2, the echo E9 of a school of fish can be displayed together with the echoes (E4 and ES) of the trawling implement 100, and further, the echoes (E4 and ES) of the trawling implement 100 can be displayed differently in the display colour from the echoes (El, E2, E3, E7, E8, and E9) of schools of fish. Therefore, the user can visually recognize easily the echo of a school of fish and the echoes of the trawling implement 100.

[0124] In the third modification of the first embodiment, as described above, the second signal processing module 13 may acquire the second echo signal from the reception signal corresponding to the reception wave which comes from the second echo signal acquisition area RX which is obtained by further limiting to the given distance range DX within the second direction range R2. However, without being limited to this example, in a further modification of the third modification of the first embodiment, the second signal processing module 13 may acquire the second echo signal from the reception signal corresponding to the reception wave which comes from the second echo signal acquisition area RX which is limited to the given distance range DX within the second direction range R2 and also limited to the given underwater depth range. In this modification, the second echo signal acquisition area RX may be an area inside the second direction range R2, and may be an area inside the given distance range DX apart from the transducer 2 as the receiving transducer, and may be also an area within the given underwater depth range. The given underwater depth range may be a depth range deeper than a first given depth and shallower than a second given depth deeper than the first given depth.

[0125] As described above, in the further modification of the third modification of the first embodiment, the second signal processing module 13 may acquire the second echo signal from the reception signal corresponding to the reception wave which comes from the second echo signal acquisition area RX which is an area limited to both the given distance range DX within the second direction range R2, and the given depth range. That is, the second signal processing module 13 may acquire the second echo signal from the reception signal corresponding to the reception wave having the incoming azimuth angle from the second direction range R2, and the reception signal corresponding to the reception wave which comes from the given distance range DX distant from the transducer 2 as the receiving transducer and which comes from the given underwater depth range.

[0126] Note that, also in the further modification of the third modification of the first embodiment, the image signal generation module 14 may generate the echo image signal based on the first echo signal and the second echo signal, similar to the third modification of the first embodiment. On the display unit 5, the echo images may be displayed based on the echo image signal generated by the image signal generation module 14.

[0127] According to the further modification of the third modification of the first embodiment, the echoes of the trawling implement 100 may be displayed only in the second echo signal acquisition area RX limited to both the given distance range DX and the given depth range in the second direction range R2. Therefore, according to the further modification of the third modification of the first embodiment, the area where the echoes of the trawling implement 100 are displayed may be limited to the further narrower area around the trawling implement 100, thereby displaying the echoes of schools of fish in a further larger area.

(Fourth Modification of First Embodiment) [0128] Fig. 18 is a view illustrating a fourth modification of the first embodiment, where processing of the fourth modification of the first embodiment is illustrated. Note that, in the following description, differences from the first embodiment will be described and the same or corresponding configurations are assigned with the same reference characters in the drawing or refer the same reference characters to suitably omit redundant description.

[0129] Fig. 18 is a view illustrating processing of the second signal processing module 13 in the fourth modification of the first embodiment. Fig. 18 is a plan view schematically illustrating the ship S and its perimeter, where the first direction range R 1 and the second direction range R2 which are set by the processings of the first signal processing module 12 and the second signal processing module 13 are schematically illustrated. Moreover, Fig. 18 illustrates the first direction range R1 and the second direction range R2 in a state where the bow direction HD changes. Note that, in Fig. 18, in order to illustrate the state of the change in the bow direction HD, a trail WA of the ship S may be also illustrated schematically.

[0130] In the fourth modification of the first embodiment, while the bow direction HD changes, the second sign& processing module 13 may change the parameter which defines the second direction range R2, based on the change in the bow direction HD to change the second direction range R2. In the fourth modification of the first embodiment, as a parameter which defines the second direction range R2 and which changes when the bow direction HD changes, the parameter of the size of the angular range of the second direction range R2 may be selected.

[0131] In more detail, in the fourth modification of the first embodiment, while the bow direction HD changes, the second signal processing module 13 may widen the angular range of the second direction range R2 more than that when the bow direction HD does not change, to change the second direction range R2. Note that, in Fig. 18, the second direction range R2 when the how direction HD changes is illustrated by a two-direction arrow R2 of a solid fine, and boundary fines at both sides of the second direction range R2 when the bow direction HD changes are illustrated by broken lines. Moreover, in Fig. 18, the second direction range R2 before the change in the bow direction HD which is in a state where the bow direction HD does not change is illustrated by a two-direction arrow R20 of a two-dot chain line, and boundary lines at both sides of the second direction range R2 before the change in the bow direction HD are illustrated by two-dot chain lines. As illustrated in Fig. 18, in the fourth modification of the first embodiment, when the bow direction HD changes, the second signal processing module 13 may widen the angular range of the second direction range R2 more than that when the how direction HD does not change, to change the second direction range R2. Note that, when the second signal processing module 13 changes the second direction range R2 when the bow direction HD changes, the first signal processing module 12 may change the first direction range R1 according to the changed second direction range R2 so that the first direction range R1 is always adjacent to the second direction range R2 in the direction of the azimuth angle 0.

[0132] According to the fourth modification of the first embodiment, while the bow direction HD changes, the second direction range R2 may be changed by changing the parameter which defines the second direction range R2, based on the change in the bow direction HD. Thus, the second direction range R2 can be changed so that the trawling implement 100 of which the relative position to the ship S changes when the how direction HD changes exists within the second direction range R2.

[0133] Further, according to the fourth modification of the first embodiment, while the bow direction HD changes, the second signal processing module 13 may widen the angular range of the second direction range R2 more than that when the bow direction HD does not change, to change the second direction range R2. Therefore, even if the relative position of the trawling implement 100 to the ship S is changed with the change in the bow direction HD, the second direction range R2 can be changed, without the trawling implement 100 being located outside the second direction range R2 so that the trawling implement 100 stably exists within the second direction range R2.

(Second Embodiment) [0134] Next, a second embodiment of the present disclosure is described. Fig. 19 is a block diagram illustrating a configuration of a signal processor 4a of the underwater detection apparatus of the second embodiment. Note that, in the description of the following second embodiment, differences from the first embodiment will be described and the same or corresponding configurations are assigned with the same reference characters in the drawing or refer the same reference characters to suitably omit redundant description.

[0135] The underwater detection apparatus of the second embodiment may differ from the underwater detection apparatus 1 of the first embodiment in the configuration of the signal processor 4a. In detail, the underwater detection apparatus of the second embodiment may differ from the underwater detection apparatus 1 of the first embodiment in that the signal processor 4a is further provided with a mark position setting module 15, and further, the image signal generation module 14 may generate a trawl mark image signal for displaying a mark of the trawling implement 100 on the display unit 5 based on a setting result of the mark position setting module 15.

[0136] The mark position setting module 15 may set a position corresponding to an echo which is identified as an echo corresponding to at least a part of the trawling implement 100 towed by the ship S as a mark setting position which is a position at which the mark of the trawling implement 100 is displayed. Then, the image signal generation module 14 may generate the echo image signals for displaying the echoes of the target objects on the display unit 5 based on the first echo signal and the second echo signal, and further may generate the trawl mark image signal for displaying the mark of the trawling implement 100 at the mark setting position set by the mark position setting module 15.

[0137] Figs. 20 and 21 are views schematically illustrating one example of the image displayed in the display screen of the display unit 5 based on processing of the underwater detection apparatus of the second embodiment. As illustrated in Figs. 20 and 21, in the second embodiment, as the three-dimensional area image displayed on the display unit 5 based on the echo image signal generated by the image signal generation module 14, three-dimensional area images (IM1, IM2, and IM3), which are viewed from a plurality of viewpoints, respectively, may be displayed on the display unit 5. The three-dimensional area image IM1 may be displayed as an image of the detection area DR from an obliquely upward viewpoint which is a viewpoint from which the detection area DR is viewed from obliquely upward of the ship S. The three-dimensional area image IM2 may be displayed as an image of the detection area DR from a vertical viewpoint which is a viewpoint from which the detection area DR is viewed from directly above the ship S. The three-dimension& area image 1M3 may he displayed as an image of the detection area DR from a horizontal viewpoint which is a viewpoint from which the detection area DR is viewed horizontally from the side of the detection area DR. In Figs. 20 and 21, the three three-dimensional area images (IM1, IM2, and IM3) may be displayed in the same display screen of the display unit 5 so as to be arranged as illustrated.

[0138] In any of the three-dimensional area images (IM1, IM2, and IM3) displayed in the display screen on the display unit 5, the echoes of the target objects may be displayed in the display screen of the display unit 5 based on the echo image signal generated by the image signal generation module 14 based on the first echo signal and the second echo signal generated by the first sign& processing module 12 and the second sign& processing module 13. In detail, in any of the three-dimensional area images (IM1, 1M2, and IM3), the echoes (El, E2, and E3) of the target objects as schools of fish may he displayed in the display screen of the display unit 5 based on the echo image signal generated by the image signal generation module 14 based on the first echo signal generated by the first signal processing module 12. In addition, in any of the three-dimension& area images (IMI, IM2, and IM3), the echoes (E4 and E5) of the target objects as the trawling implement 100 may be displayed in the display screen of the display unit 5 based on the echo image signal generated by the image signal generation module 14 based on the second echo signal generated by the second signal processing module 13. Note that, in Figs. 20 and 21, as the echoes (E4 and ES) corresponding to the second echo signals, the echoes of the otter boards 101 of the trawling implement 100 may be displayed.

[0139] Note that, in this embodiment, the three three-dimensional area images (IM1, IM2, and IM3) may be displayed on the display unit 5. The three-dimensional area images (IM1, 1M2, and IM3) displayed on the display unit 5 may suitably be switched therebetween based on operation of the user. For example, when the user suitably operates the user interface (not illustrated) provided to the underwater detection apparatus of this embodiment, such as the keyboard or the pointing device, all of the three-dimensional area images (IM1, IM2, and IM3) may be displayed on the display unit 5, or arbitrary one or two of the three-dimensional area images (IMI, 1M2, and IM3) may he displayed.

[0140] The mark position setting module 15 may set the position corresponding to the echo identified as the echo corresponding to at least a part of the trawling implement 100 as the mark setting position which is the position at which the mark of the trawling implement 100 is displayed. When setting the mark setting position, the mark position setting module 15 may identify the echo corresponding to at least a part of the trawling implement 100 based on operation by the user of the underwater detection apparatus, and may set the mark setting position. Alternatively, for example, the mark position setting module 15 may identify the echo among the echoes detected in the second direction range R2, of which the signal intensity level exceeds a given value, as the echo corresponding to at least a part of the trawling implement 100, and may set the mark setting position. Note that, in the second embodiment, the mark position setting module 15 may identify the echo corresponding to at least a part of the trawling implement 100 based on operation by the user of the underwater detection apparatus, and set the mark setting position.

[0141] When setting the mark setting position, the mark position setting module 15 may identify, based on an input by operation in which the user of the underwater detection apparatus selects an echo, the selected echo as the echo corresponding to the trawling implement 100, and may set the mark setting position. In more detail, the user first may operate the pointing device, such as a mouse, provided to the underwater detection apparatus, to move the position of a cursor displayed in the display screen of the display unit 5 to a position of the echo E4 or E5 in the three-dimensional area image 1M3 viewed from the horizontal viewpoint. Then, the user may perform a click operation of the pointing device on the echo E4 or ES to which the cursor is moved, to select the echo E4 or ES. By this operation, the operation in which the echo E4 or E5 is selected may be inputted into the signal processor 4a. Once this input is made, the depth of the otter hoard 101 of the trawling implement 100 corresponding to the echo E4 or ES may be determined [0142] Then, the user may select, in the three-dimensional area image IM1 from the obliquely upward viewpoint or the three-dimensional area image IM2 viewed from the vertical viewpoint, the same echo as the echo selected in the three-dimensional area image IM3 viewed from the horizontal viewpoint. Thus, the horizontal distance and the azimuth angle 0 of the otter board 101 from the ship 5, corresponding to the echo E4 or echo E5 selected by the user. may be determined.

[0143] As described above, the user may perform the selecting operation of the echo E4 or E5 in the three-dimensional area image IM3 of the horizontal viewpoint, and the selecting operation of the echo E4 or ES in the three-dimensional area image IM1 of the obliquely upward viewpoint or the three-dimensional area image IM2 of the vertical viewpoint, so that the depth, the horizontal distance, and the azimuth angle 0 of the otter board 101 from the ship S corresponding to the echo E4 or E5 are determined. Therefore, the coordinates of the otter board 101 corresponding to the echo E4 or E5 may be determined. Then, the user may perform a similar operation to the other one of the echo E4 and E5 corresponding to the otter board 101 of which the coordinates was determined. For example, if the selecting operation in the three-dimensional area image 1M3 of the horizontal viewpoint and the selecting operation in the three-dimensional area image IM1 of the obliquely upward viewpoint or the three-dimensional area image IM2 of the vertical viewpoint are first performed for the echo E4, and the coordinates of the otter board 101 corresponding to the echo E4 are determined, the similar operation is subsequently performed for the echo ES by the user. Thus, for the echo E5 as well as the echo E4, the selecting operation in the three-dimensional area image IM3 of the horizontal viewpoint, and the selecting operation in three-dimensional area image IM I of the obliquely upward viewpoint or the three-dimensional area image IM2 of the vertical viewpoint may be performed, thereby determining the depth, the horizontal distance, and the azimuth angle 0 of the otter board 101 from the ship S corresponding to the echo E5. Therefore, the coordinates of the otter board 101 corresponding to the echo E5 may he also determined.

[0144] As described above, the mark position setting module 15 may identify, based on the input by the operation in which the echoes (E4 and ES) are selected by the user of the underwater detection apparatus, the selected echoes (E4 and ES) as the echoes corresponding to the otter boards 101 of the trawling implement 100. Then, the mark position setting module 15 may set the mark setting positions at the positions of the coordinates of the otter boards 101 corresponding to the echoes (E4 and ES). Note that, although in the second embodiment the user sequentially selects the echoes E4 and ES, and the mark position setting module sets the mark setting positions at the positions of the coordinates of the two otter boards 101 corresponding to the echoes E4 and ES, respectively, the configuration may be altered. For example, the user may select only one of the echoes E4 and ES, and the mark position setting module 15 may set the mark setting position at the position of the coordinates of one otter board 101 corresponding to the selected echo.

[0145] As described above, once the setting of the mark setting position is performed by the mark position setting module 15, the image signal generation module 14 may generate the trawl mark image signal for displaying marks TM of the trawling implement 100 at the mark setting position. Note that the trawl mark image signal may also include information on the mark setting position set by the mark position setting module 15. In Fig. 21, the marks TM of the trawling implement 100 may be displayed in each of the three-dimensional area images (IM1, IM2, and IM3) of the obliquely upward viewpoint, the vertical viewpoint, and the horizontal viewpoint. Moreover, Fig. 22 is an enlarged view illustrating a part of the example of the image illustrated in Fig. 21, and is an enlarged view of the three-dimensional area image 1M1.

[0146] When the image signal generation module 14 generates the trawl mark image signal for displaying the marks TM of the trawling implement 100, it then may output the generated trawl mark image signal to the display unit 5. The display unit 5 may display the mark TM indicative of the trawling implement 100 at the mark setting position set by the mark setting module 15 in each of the three-dimensional area images (IM1, IM2, and 1M3) based on the inputted trawl mark image signal.

[0147] As illustrated in Figs. 21 and 22, the image signal generation module 14 may generate the trawl mark image signals for displaying marks MI and M2 as the marks TM of the trawling implement 100 on the display unit 5. The mark Ml may be a mark of the otter board 101, and a mark M2 may he a mark of the net mouth 102a of the net 102. Moreover, the image signal generation module 14 of the second embodiment may also generate the trawl mark image signals for displaying on the display unit 5, together with the mark Ml and the mark M2, marks M3 and M4 which are marks other than the mark Ml of the otter board 101 and the mark M2 of the net mouth 102a. Note that the mark M3 may be a mark of the warp 103, and the mark M4 may be a mark of the wire 104. Note that, in Figs. 21 and 22, the marks (MI, M2, M3, and M4) may be illustrated by two-dot chain lines.

[0148] Moreover, the image signal generation module 14 may assign to the marks (M1, M2, M3, and M4) different colours from the colours assigned to the echoes (El, E2, E3, E4, and ES) of the target objects to generate the trawl mark image signal. That is, the echo image signals for displaying the echoes (El, E2, E3, E4, and ES) and the trawl mark image signals for displaying the marks (M I, M2, M3, and M4) may include information on different colours as the information on the display colours to be displayed on the display unit 5. On the display unit 5, the images of the marks (M1, M2, M3, and M4) may be displayed in the colours based on the information on the display colours contained in the trawl mark image signals. For example, on the display unit 5, the background colour of the display screen may be black, the echoes (El, E2, E3, E4, and E5) may be in red, green, and blue, and the marks (Ml, M2, M3, and M4) may be in white.

[0149] Note that various settings used for the image signal generation module 14 generating the trawl mark image signal for displaying the marks (M I, M2, M3, and M4) may be stored in the signal processor 4a. However, the various settings described above may be changed, for example, by the user suitably operating the user interface provided to the underwater detection apparatus, such as the keyboard or the pointing device. The various settings include, for example, a distance between the mark Ml of the otter board 101 and the mark M2 of the net mouth 102a, the size of the mark MI of the otter board 101 (i.e., each dimension of the height, the length, and the thickness of the mark Ml of the otter board 101), the size of the mark M2 of the net mouth 102a (i.e., each dimension of the width and the height of the mark M2 of the net mouth 102a), and the angle of the inclination of the mark M2 of the net mouth 102a to the vertical plane.

[0150] Moreover, the image signal generation module 14 may also generate image signals for displaying on the display unit 5 vertical planes (VS I, VS2) including the mark setting positions at which the mark Ml of the otter boards 101 is displayed, in addition to the echo image signals for displaying the echoes (El-E5) of the target objects and the trawl mark image signals for displaying the marks (Ml-M4). In the second embodiment, the vertical planes (VS1 and VS2) may be displayed in the three-dimensional area image IM1 displayed on the display unit 5. The vertical plane VS1 may be constituted as a plane including a vertical line extending vertically downward from the position directly underneath the ship S, and a vertical line extending vertically upward and downward from the centre position of the mark MI of the otter board 101 corresponding to the echo E4. Moreover, the vertical plane VS2 may be constituted as a plane including a vertical line extending vertically downward from the position directly underneath the ship S, and a vertical line extending vertically upward and downward from the centre position of the mark Ml of the otter board 101 corresponding to the echo E5. On the display unit 5, the vertical planes (VS1 and VS2) may be displayed in the three-dimensional area image IM1 based on the image signal generated by the image signal generation module 14, along with the echoes (E1-E5) and the marks (Ml-M4) of the target objects.

[0151] Moreover, the image signal generation module 14 may also generate a cross-sectional image signal for displaying on the display unit 5 the echo of the target object included in the vertical planes (VS I and VS2). In more detail, the image signal generation module 14 may generate the cross-sectional image signal for displaying on the display unit 5 the echo E4 of the target object as the otter board 101 included in the vertical plane VS1. The image signal generation module 14 may also generate the cross-sectional image signal for displaying on the display unit 5 the echo E5 of the target object as the otter board 101 included in the vertical plane VS2. In Fig. 21, cross-sectional images (IM4 and IM5) displayed in the display screen of the display unit 5 based on the cross-sectional image signals generated by the image signal generation module 14 may be illustrated.

[0152] The cross-sectional image IM4 may be displayed based on the cross-sectional image signal for displaying on the display unit 5 the echo E4 of the target object as the otter board 101 included in the vertical plane VS I. The cross-sectional image IM5 may he displayed based on the cross-sectional image signal for displaying on the display unit 5 the echo E5 of the target object as the otter board 101 included in the vertical plane VS2. In the cross-sectional image IM4, an image of a cross-section of the echo E4 at the vertical plane VS1 may be displayed. In the cross-sectional image IM5, an image of a cross-section of the echo E5 at the vertical plane VS2 may be displayed. Thus, since the user who looked at the image displayed on the display unit 5 can visually observe the cross-sectional images (IM4 and IM5) along with the three-dimensional area images (IM I, IM2, and IM3), he/she can grasp in more detail the state of the otter board 101 of the trawling implement 100.

[0153] Moreover, in the second embodiment, while the how direction HD changes, the mark position setting module 15 may rotate the mark setting position centring on a rotation centre position set at the position corresponding to the position of the ship S. Figs. 23 and 24 are views illustrating processing of the mark position setting module 15 in the signal processor 4a of the underwater detection apparatus of the second embodiment, where the processing to rotate the mark setting position is illustrated.

[0154] When the mark position setting module 15 performs the processing to set the mark setting positions at the positions of the coordinates of the otter boards 101 based on the selecting operation of the echoes (E4 and E5) by the user, it may then perform the processing to rotate the mark setting positions when the bow direction HD changes. In this processing, once the mark position setting module 15 sets the mark setting positions, it may first identify the position of a midpoint PI of the two otter boards 101, as illustrated in Fig. 23. The position of the midpoint P1 of the two otter boards 101 may be identified as a midpoint between a centre position of the mark Ml when displaying the mark Ml corresponding to the echo E4 and a centre position of the mark M1 when displaying the mark M1 corresponding to the echo ES.

[0155] The mark position setting module 15 may then obtain a horizontal distance between the midpoint PI and the ship S. Note that the horizontal distance between the ship S and the midpoint P1 may be a horizontal distance between the ship S and the midpoint P1 when the ship S and the two otter hoards 101 are viewed perpendicularly to the horizontal direction as illustrated in Fig. 23. The mark position setting module 15 may then identify an equidistant trail point P2 which is a point on a trail WA of the ship S, which is located at the same distance from the ship S as the horizontal distance. Note that, in Fig. 23, the distance from the ship S may be illustrated by a circle EDL of a two-dot chain line, which is drawn by connecting a set of points located at the same distance as the horizontal distance.

[0156] The ship S may carry a GPS antenna (not illustrated) which receives radio waves (positioning signals) transmitted from the positioning satellites, and a GPS receiver (not illustrated) which detects the position of the ship S based on the positioning signals received by the GPS antenna. The GPS receiver may he connected to the signal processor 4a, and may output the detected position of the ship S to the signal processor 4a. The signal processor 4a may acquire the data of the trail WA of the ship S as time series data of the position of the ship S inputted from the GPS receiver. When the mark position setting module 15 calculates the equidistant trail point P2, it may search for a position of an intersection at which the trail WA first crosses the circle EDL, along the trail WA from the ship S. The mark position setting module 15 may obtain this intersection as the equidistant trail point P2.

[0157] Then, the mark position setting module 15 may set an angle formed by the stern direction TD, and an equidistant trail point direction WD which is a direction of the equidistant trail point P2 from the ship S, as an initial angle 00. Note that, in Fig. 23, the equidistant trail point direction WD may be illustrated by a broken line, and the stern direction TD may be illustrated by a one-point chain line. The mark position setting module 15 may obtain the initial angle 00 at a timing where the mark setting position is set based on the selecting operation of the echoes (E4 and E5) by the user.

[0158] Note that, if the bow direction HD does not change during a period from a time when the ship S passes through the position corresponding to the equidistant trail point P2 to a time when the mark position setting module 15 sets the mark position, the initial angle 00 may be zero. In this case, once setting the mark setting position, the mark position setting module 15 may not rotate the mark setting position, unless the bow direction HD changes.

[0159] On the other hand, while the bow direction HD changes after the setting of the mark setting position, the mark position setting module 15 may rotate the mark setting position, as illustrated in Fig. 24. The rotation of the mark setting position while the bow direction HD changes may be performed each time the data of the bow direction is acquired by the data acquisition module 10.

[0160] Each time the mark position setting module 15 acquires the data of the bow direction, as illustrated in Fig. 24, it may obtain the equidistant trail point P2, and may obtain an angle 01 formed by the stern direction TD, and the equidistant trail point direction WD which is a direction of the equidistant trail point P2 from the ship S, as a bow direction change angle 01. Note that, the equidistant trail point P2 may be obtained by similar processing to the case where the initial angle 00 is set after setting the mark setting position, also while the bow direction HD changes. The mark position setting module 15 may then rotate the mark setting position centring on the rotation centre position set as the position corresponding to the position of the ship S by an angle difference (01-00) between the bow direction change angle 01 and the initial angle 00. Note that, in Fig. 24, as for the two otter boards 101 and the midpoint P1 thereof, the mark setting positions may be rotated by the angle difference (01-00) when the bow direction HD changes.

[0161] The image signal generation module 14 may then generate the trawl mark image signal for displaying the marks Ml of the two otter boards 101 of the trawling implement 100 at the mark setting positions which are rotated centring on the position of the ship S. The image signal generation module 14 may also generate the trawl mark image signal for displaying the mark M2 of the net mouth 102a, the marks M3 of the warps 103, and the marks M4 of the wires 104 at the positions which are rotated centring on the position of the ship S, corresponding to the marks Ml of the otter boards 101. The generated trawl mark image signal may be outputted to the display unit 5, and on the display unit 5, the marks TM of the trawling implement 100 and the marks M3 of the warps 103 may he displayed at the positions which are rotated centring on the position of the ship S. That is, when the bow direction HD changes, on the display unit 5, the marks Ml of the two otter boards 101, the mark M2 of the net mouth 102a, the marks M3 of the warps 103, and the marks M4 of the wires 104 may be displayed at the positions which are rotated centring on the position of the ship S, according to the change in the bow direction.

[0162] The underwater detection apparatus of the second embodiment may be constituted as the underwater detection apparatus used in the trawling ship S, similar to the underwater detection apparatus 1 of the first embodiment, and provided with the transducer 2 and the second signal processing module 13. The underwater detection apparatus of the second embodiment may further be provided with the image signal generation module 14 and the mark position setting module 15, which are described above. Therefore, the underwater detection apparatus of the second embodiment may include the transducer 2 as the transmitting transducer which transmits the transmission wave toward the underwater trawling implement 100, the transducer 2 as the receiving transducer which receives the reception wave including the reflection of the transmission wave on the trawling implement 100 and generates the reception signal from the received reception wave, the second signal processing module 13 as the signal processing module which acquires the echo signal from the reception signal, the image signal generation module 14 which generates the echo image signal based on the echo signal, and the mark position setting module 15 which sets the position corresponding to the echo identified as the echo corresponding to at least a part of the trawling implement 100 as the mark setting position which is the position on which the marks TM of the trawling implement 100 are displayed. The image signal generation module 14 may further generate the trawl mark image signal for displaying the marks TM of the trawling implement 100 at the mark setting position, and while the bow direction HD changes, the mark position setting module 15 may rotate the mark setting position centring on the rotation centre position set as the position corresponding to the position of the ship S. [0163] According to the second embodiment, the marks TM of the trawling implement 100 can he displayed at the positions corresponding to the echoes (E4 and E5) identified as the echoes (E4 and E5) corresponding to the trawling implement 100. Therefore, since the user can visually observe the echoes (E4 and E5) of the trawling implement 100 with the marks TM of the trawling implement 100, he/she can grasp the state of the trawling implement 100 more easily and clearly.

[0164] Moreover, according to the second embodiment, while the bow direction HD changes, the marks TM of the trawling implement 100 can be rotated centring on the position of the ship S, according to change in the bow direction HD, and the rotated marks TM can be displayed. Therefore, the user can grasp more easily and clearly that the direction of the trawling implement 100 changes with respect to the ship S, while the how direction HD changes.

(Modification of Second Embodiment) [0165] Fig. 25 is a view illustrating a modification of the second embodiment, where processing of the modification of the second embodiment is illustrated. Note that, in the following description, differences from the first embodiment, the second modification of the first embodiment, and the second embodiment will be described, and the same or corresponding configurations are assigned with the same reference characters in the drawing or refer the same reference characters to suitably omit redundant description.

[0166] Fig. 25 is a view illustrating processing of the image signal processing part 14 in the modification of the second embodiment. In Fig. 25, the three-dimensional area image IM1 including the echoes (El, E2, E3, and E7) of the target objects as schools of fish, and the marks TM of the trawling implement 100 may be displayed on the display unit 5 based on the echo image signals and the trawl mark image signals which are generated by the image signal generation module 14.

[0167] In the modification of the second embodiment, similar to the second modification of the first embodiment, the first signal processing module 12 may set the first direction range R1 from which the first echo signal is acquired as a direction range covering all directions of the azimuth angle 0. In the modification of the second embodiment, similar to the second modification of the first embodiment, the first direction range R I and the second direction range R2 may have an overlapping direction range, and schools of fish may be detected also in the area for detecting the trawling implement 100. That is, as illustrated in Fig. 25, the echo E7 of the school of fish detected in the second direction range R2 can also be displayed on the display unit 5.

[0168] Moreover, in the modification of the second embodiment, the state can be switched, based on operation of the user, between a display ON state in which the echoes (E4 and E5) of the trawling implement 100 are displayed on the display unit 5 and a display OFF state in which the echoes (E4 and ES) are not displayed. In the display ON state, the echoes (E4 and ES) of the trawling implement 100 and the marks TM of the trawling implement 100 may be displayed on the display unit 5 based on the echo image signals and the trawl mark image signals which are generated by the image signal generation module 14, similar to the second embodiment.

[0169] On the other hand, when the state is switched from the display ON state to the display OFF state, the indication of the marks TM of the trawling implement 100 may be maintained, but the echoes (E4 and ES) of the trawling implement 100 are not displayed (see Fig. 25). The switching of the state from the display ON state to the display OFF state by the user may be performed, for example, by the user suitably operating the user interface, such as the keyboard or the pointing device. Note that, switching operation from the display ON state to the display OFF state may be performed after the marks TM of the trawling implement 100 are once displayed on the display unit 5.

[0170] When the switching operation from the display ON state to the display OFF state is performed by the user, the image signal generation module 14 may generate the echo image signals for displaying the echoes (El, E2, E3, and E7) of the target objects as schools of fish based on the first echo signals, and the trawl mark image signals for displaying the marks TM of the trawling implement 100, and then output them to the display unit 5. Then, in the display OFF state, the image signal generation module 14 may not perform the generation of the echo image signals for displaying the echoes (E4 and E5) of the target objects as the trawling implement 100 on the display unit 5 based on the second echo signal. Therefore, in the display OFF state, on the display unit 5, the echoes (El, E2, E3, and E7) of schools of fish and the marks TM of the trawling implement 100 may be displayed, and the echoes (E4 and E5) of the trawling implement 100 may not displayed.

[0171] Moreover, in the modification of the second embodiment, even in the display OFF state where the marks TM of the trawling implement 100 are displayed and the echoes (E4 and E5) of the trawling implement 100 are not displayed, the mark position setting module 15 may rotate the mark setting positions when the bow direction HD changes. Then, the image signal generation module 14 may generate the trawl mark image signals for displaying the marks TM of the trawling implement 100 at the mark setting positions which are rotated centring on the position of the ship S, and output them to the display unit 5. Therefore, on the display unit 5, the marks TM of the trawling implement 100 may be displayed at the positions which are rotated centring on the position of the ship S, according to the change in the bow direction HD.

[0172] According to the modification of the second embodiment, by changing the state from the display ON state to the display OFF state, the echoes (El, E2, E3, and E7) of schools of fish and the marks TM of the trawling implement 100 may be displayed, but the echoes (E4 and E5) of the trawling implement 100 may not be displayed, on the display unit 5. Therefore, schools of fish can be detected in the large first direction range R1 including the second direction range R2 and the detected echoes (El, E2, E3, and E7) can be displayed. In addition, the trawling implement 100 can also be displayed as the marks TM of the trawling implement 100 which can be easily distinguished from the echoes.

(Other Modifications) [0173] As described above, although the embodiments and their modifications of the present disclosure are described, the present disclosure is not limited to the above configurations and various changes may be made without departing from the spirit of the present disclosure.

[0174] (1) In the above embodiments and their modifications, the underwater detection apparatus provided with the transducer which functions as the transmitting transducer and also functions as the receiving transducer is described, but the configuration may be altered. For example, the underwater detection apparatus may be provided with the transmitting transducer and the receiving transducer separate from each other.

[0175] (2) In the above embodiments and their modifications, although the underwater detection apparatus is provided with the scanning sonar which forms the transmission beam all at once toward all the underwater directions centring on the ship, the configuration may he altered. For example, the underwater detection apparatus may be provided with a searchlight sonar (PPI sonar) which rotates the transmission beam and the reception beam. Moreover, in the above embodiments and their modifications, although the underwater detection apparatus is provided with the three-dimensional scanning sonar, the configuration may be altered. For example, the underwater detection apparatus may he provided with two-dimensional scanning sonar.

[0176] (3) In the above embodiments and their modifications, although the second signal processing module sets the second direction range in the direction range centring on the stern direction, the configuration may be altered. For example, the second signal processing module may obtain a direction from the ship as an intersection of a circle with a radius equal to the warp length centring on the position of the ship with the trail of the ship, and set the second direction range in the direction range centring on the direction of the intersection from the ship. Alternatively, the second signal processing module may calculate an angle difference between the direction of the intersection from the ship and the stern direction, and set the second direction range further wider by a given multiple of the angle difference. [0177] (4) In the above embodiments and their modifications, although the warp length of the warps is measured by the warp length measuring instrument provided with the encoder which detects the number of rotations of the top rollers which is provided at the stern of the ship and rotates when sending out and winding up the warps, the configuration may he altered. For example, when the input of selecting the echoes of the otter hoards is performed by the user, the distance between the ship and the otter boards may be calculated based on the input to calculate the warp length.

[0178] (5) In the second embodiment and its modification, although the marks of the trawling implement are displayed together with the echoes of the schools of fish, numerical information on the trawling implement may further be displayed together with the marks of the trawling implement. In this case, the numerical information, such as the distance in the straight line between the ship and the otter board, the horizontal distance between the ship and the otter board, the depth of the otter board or the net mouth, and the distance between the two otter hoards, may he displayed together with the marks of the trawling implement. [0179] (6) In the modification of the second embodiment, similar to the third modification of the first embodiment, the second signal processing module 13 may further acquire the second echo signal from the reception signal corresponding to the reception wave having the incoming azimuth angle from the second direction range R2, and the reception signal corresponding to the reception wave which came from the given distance range DX which is distant from the transducer 2 as the receiving transducer. Moreover, in this case, the width of the distance may be set by the operation of the user among the centre value of the distance and the width of the distance which define the given distance range DX, and the centre value of the distance may be set as the distance between the mark setting position which is set by the mark position setting module 15, and the ship S. [0180] (7) The image signal generation module may perform known signal processing or known image processing, such as TVG (Time Varied Gain) and interference removal, to the first echo signal and the second echo signal. Alternatively, the image signal generation module may perform these processings on a condition in which the effects to the first echo signal and the second echo signal are different.

[0181] The present disclosure may widely be applicable to the underwater detection apparatus and the underwater detection method, which detect the underwater target object.

Claims

Cairns: 1. An underwater detection apparatus (1) to he used on a ship, comprising: a transmission transducer (2) configured to transmit an underwater transmission wave; a reception transducer (2) configured to receive a reception wave comprising a reflection of the transmission wave on an underwater target and configured to generate a reception signal from the received reception wave; a Doppler shift calculation module (11) configured to calculate a frequency shift amount by which a frequency of the reception wave is shifted relative to a frequency of the transmission wave; a first signal processing module (12) configured to retrieve a first echo signal from the reception signal based on the frequency shift amount, the first echo signal being retrieved from the reception signal corresponding to the reception wave having an incoming azimuth angle from within a first direction range; a second signal processing module (13) configured to retrieve a second echo signal from the reception signal independently of the frequency shift amount, the second echo signal being retrieved from the reception signal corresponding to the reception wave having an incoming azimuth angle from within a second direction range different from the first direction range; and an image signal generation module (14) configured to generate an echo image signal to display an echo of the target on a display unit based on the first echo signal and the second echo signal.
2. The underwater detection apparatus (1) of claim 1, wherein: the first direction range includes a heading direction of the ship and the second direction range includes a stern direction of the ship.
3. The underwater detection apparatus (1) of claim 1 or claim 2, wherein: when a heading direction of the ship changes, the second signal processing module (13) changes the second direction range by changing a parameter that specifies the second direction range based on the heading direction change.
4. The underwater detection apparatus (1) of any of the preceding claims, wherein: when a heading direction of the ship changes, the second signal processing module (13) changes the second direction range by changing a direction of a centre line that bisects the second direction range in two halves of equal range based on the heading direction change.
5. The underwater detection apparatus (1) of any of the preceding claims, wherein: when a heading direction of the ship changes clockwise, the second signal processing module (13) changes the second direction range by changing counter clockwise a direction of a centre line that bisects the second direction range in two halves of equal range.
6. The underwater detection apparatus (1) of any of the preceding claims, wherein: when a heading direction of the ship changes, the second signal processing module (13) changes the second direction range by widening an angular range of the second direction range compared to when the heading direction of the ship does not change.
7. The underwater detection apparatus (1) of any of the preceding claims, wherein: an angular range of the first direction range is wider than an angular range of the second direction range.
8. The underwater detection apparatus (1) of any of the preceding claims, wherein: the first signal processing module (12) retrieves the first echo signal: by mixing the reception signal with a local signal having a frequency adjusted based on the frequency shift amount, or by filtering the reception signal, a frequency characteristic of the filtering being adjusted based on the frequency shift amount.
9. The underwater detection apparatus (1) of any of the preceding claims, wherein: the second signal processing module (13) retrieves the second echo signal: by mixing the reception signal with a local signal having a fixed frequency set based on the frequency of the transmission wave, or by filtering the reception signal, a frequency characteristic of the filtering being adjusted based on the frequency of the transmission wave.
10. The underwater detection apparatus (1) of any of the preceding claims, further comprising: a data acquisition module (10) configured to acquire at least one of a ship speed data of the ship and a warp length data of a warp connected between the ship and a trawl gear towed by the ship, wherein: the second signal processing module (13) retrieves the second echo signal by limiting a frequency band of the reception signal, the frequency band being adjusted based at least on one of the ship speed data and the warp length data.
11. The underwater detection apparatus (1) of claim 10, wherein: in a first situation in which the ship speed is faster than in a second situation, the frequency band is narrower than in the second situation.
12. The underwater detection apparatus (1) of claim 10 or claim 11, wherein: in a third situation in which the warp length is shorter than in a fourth situation, the frequency band is narrower than in the fourth situation.
13. The underwater detection apparatus (1) of any of the preceding claims, wherein: the image signal generation module (14) generates the echo image signal by allocating colours to the echo of the target corresponding to the first echo signal that are different from colours allocated to the echo of the target corresponding to the second echo signal.
14. The underwater detection apparatus (1) of any of the preceding claims, wherein: the second direction range has an angular range that overlaps the first direction range.
15. The underwater detection apparatus (1) of any of the preceding claims, further comprising: a mark position setting module (15) configured to set a position of an echo identified as an echo corresponding to at least a part of a trawl gear towed by the ship as a set mark position where a mark of the trawl gear is to be displayed, wherein: the image signal generation module (14) further generates a trawl mark image signal to display the mark of the trawl gear at the set mark position.
16. The underwater detection apparatus (1) of claim 15, wherein: when a heading direction of the ship changes, the mark position setting module (15) rotates the set mark position around a centre of rotation set at a position corresponding to a position of the ship.
17. The underwater detection apparatus (1) of any of the preceding claims, wherein: the second signal processing module (13) retrieves the second echo signal from the reception signal corresponding to the reception wave coming from within a given distance range from the reception transducer (2).
18. The underwater detection apparatus (1) of claim 17, wherein: the second signal processing module (13) retrieves the second echo signal from the reception signal corresponding to the reception wave coming from within a given underwater depth range.
19. The underwater detection apparatus (1) of any of the preceding claims, wherein: the first direction range includes the second direction range.
20. An underwater detection apparatus (1) to be used on a ship for trawl fishing, comprising: a transmission transducer (2) configured to transmit a transmission wave toward an underwater trawl gear; a reception transducer (2) configured to receive a reception wave comprising a reflection of the transmission wave on the trawl gear and configured to generate a reception signal from the received reception wave; a signal processing module (13) configured to retrieve an echo signal from the reception signal; an image signal generation module (14) configured to generate an echo image signal based on the echo signal; and a mark position setting module (15) configured to set a position of an echo identified as an echo corresponding to at least a part of the trawl gear as a set mark position where a mark of the trawl gear is to he displayed, wherein: the image signal generation module (14) further generates a trawl mark image signal to display the mark of the trawl gear at the set mark position; and when a heading direction of the ship changes, the mark position setting module (15) rotates the set mark position around a centre of rotation set at a position corresponding to a position of the ship.
21. An underwater detection method, comprising: transmitting an underwater transmission wave; receiving a reception wave comprising a reflection of the transmission wave on an underwater target and generating a reception signal from the received reception wave; calculating a frequency shift amount by which a frequency of the reception wave is shifted relative to a frequency of the transmission wave; retrieving a first echo signal from the reception signal based on the frequency shift amount, the first echo signal being retrieved from the reception signal corresponding to the reception wave having an incoming azimuth angle from within a first direction range; retrieving a second echo signal from the reception signal independently of the frequency shift amount, the second echo signal being retrieved from the reception signal corresponding to the reception wave having an incoming azimuth angle from within a second direction range different from the first direction range; and generating an echo image signal to display an echo of the target on a display unit based on the first echo signal and the second echo signal.