GB2525757A

GB2525757A - Underwater detection apparatus, underwater detection method and underwater detection program

Info

Publication number: GB2525757A
Application number: GB1506846.3A
Authority: GB
Inventors: Yong Wang
Original assignee: Furuno Electric Co Ltd
Current assignee: Furuno Electric Co Ltd
Priority date: 2014-04-25
Filing date: 2015-04-22
Publication date: 2015-11-04
Anticipated expiration: 2035-04-22
Also published as: JP2015210143A; GB2525757B; JP6469357B2; GB201506846D0

Abstract

This is for an underwater detector that can detect, amongst other things, fish or schools of fish. It is designed to compensate for the swaying, rocking, rolling or heaving of a boat or vessel on the water. The boat 90 has a transmitting and receiving device 100 attached to it. The transmission-reception surface of this device is divided so that it forms a plurality of channels that emit ultrasound signals simultaneously. It also has an attitude detection unit that can detect the attitude of the boat at the instant when it receives the echo signal. It then uses an echo signal analysis unit to analyse the signal and uses that to determine what objects, if any have been detected. The echo signal analysis unit uses a relative coordinate system and converts that to an absolute static coordinate system relative to the earth by using a coefficient that was obtained based on the attitude.

Description

Underwater Detection Apparatus, Underwater Detection Method and Underwater Detection Program

HELD OF THE NVENTON

[0001]The present invention relates to an underwater detection apparatus. an underwater detection method and an underwater detection program which emit ultrasound signals into the water and perform underwater detections based on echo signals reflected by objects.

BACKGROUND OF THE INVENTION

[0002]Nowadays, various kinds of underwater detection apparatuses are used.

Underwater detection apparatuses transmit ultrasound gnals into the water and detect target objects in the water based on echo signals reflected thereby. As targets to be detected, there are, for instance, a school of fish or a single fish. Such underwater detection apparatuses are requfted to further improve their performances. For instance, there are being devised kinds of underwater detection apparatuses which are capabie of measuring the vSodty of a moving single fish and of distinguishing and determining kinds of fish and the like.

[0003]An underwater detection apparatus emits ultrasound signals into the water and receives echo signals from objects by means of a transmitting and receiving device installed on a ship. The present invention wiU be explained as embodied, for instance, in a quantitative fish finding apparatus hereinafter.

[0004]When the ship is not swaying, the transmitting and receiving device emits an ultrasound signal in a vertical direction orthogonal to the horizontal plane, with the vertical direction coinciding with the central axis of the directional characteristics thereof. The transmitting and receMng device comprises an ultrasound transducer having the transmftting and receiving surface thereof in parallel with the horizontal plane and being divided into a plurality of transducer e!ernents which form chann&s. The underwater detection apparatus detects the position of a target object in a thre&dimensionai underwater space based on the amplitudes of echo signals received by the respective channels and on phase differences between the signals received respectively by the channels.

[0005]Further the underwater detection apparatus performs calculations to obtain the target strength Ts based on the amplltude of echo signals and the like, and calculates an observation incidence angle 9 of an uftrasound signal from a thre&dimensional position thereof, which are utllized to recognize kinds of fish and the Uke.

[0006]lt is to be noted that fishing vessels sway due to waves and swell. Thus, the transmitting and receiving device installed on the vessel also sways. In this case, the center axis of the directional characteristics of an uftrasound signal will be displaced with respect to the vertical direction, with amounts of the dispfticernent varied depending on the sway movements of the vesseL [0007]With a quantitative fish finder described in a Japanese unexamined patent pubhcation 2OO53OU222, there are calculated roll angles and pitch angles of a ship when it moves due to sways thereof, The quantitative fish finder in the Japanese patent pubilcation adjusts the phases of ultrasound signals emitted from the respective channels and also the phases of echo sign&s received by the respective channels based on the roll and pitch angles obtained so that the center axis of the directional characteristics of the transmission or reception signal beams will be coincided with the vertical downward direction.

[0008lHowever, the quantitative fish finder disclosed in the patent publication is configured to control the phases of uftrasound signals emitted and the phases of the signals received so that control processes of the signals for the transmission and reception thereof will be complicated and buiksome. 9.

SUMMARY OF THE NVENTON

[0009]Accordingly an object of the present invention is to provide an underwater detection apparatus an underwater detection method and an underwater detection program which are capable of calculating at high precision to obtain kinds of detailed data r&athig to objects to be detected without performing compcated transmission and reception controls, [OCIOjIn order to solve the foregoing problems, a first aspect of the present invenUon is to provide an underwater detection apparatus which comprises a transmitting and receiving device having the transmissionreception surface divided to form a plurauty of channels for emitting simultaneously an ultrasound signal from the respective chann&s into the water and receiving an echo signal in response to the ultrasound signal, an attitude detection unit for detecting an attitude of the transmithng and receiving device at a reception time instant when the echo signal received in the absolute static coordinate system, and an echo signal analysis unit for calculating from the echo signal the observation vector starting at the transmitting and receiving device and ending at an abject to be detected in a relative coordinate system and for converting the observation vector in the relative coordinate system to a corresponding observation vector in the absolute static coordinate system by using the conversion coefficient between the absolute static coordinate system and the relative coordinate system obtained based on the attitude.

[OO11]With the construction of the underwater detection apparatus, there is displayed the observation vector obtained based on the echo signals from an object to be detected in the absolute static coordinate system. Thus, the respective observation vectors will be obtained at a plurality of time instants in the same coordinate system. Accordingly, there wiU be suppressed influences due to the ships sways to an observation vector obtained at any one of the time instants.

[0012]A second aspect of the present invention is to provide the underwater detection apparatus in which the echo signal analysis unit of the first aspect obtains the observation vectors of a target to be detected at a plurality of time instants in the absolute static coordinate system, and calculates the velocity vector based on the observation vectors obtained at the pluraty of time instants in the absolute static coordinate system.

[0013]With the construction of the underwater detection apparatus as the observation vectors are obtained at a pluraUty of time instants in the same coordinate system, influences due to the ships sways to the veiocity vector wi be suppressed so that the velocity vector will be accurately calculated, [OO14 A third aspect of the present invention is to provide the underwater detection apparatus in which the echo signal analysis unit of the second aspect calculates the observation incidence angle of the target to be detected based on the observation vectors and the velodty vector in the absolute static coordinate system.

[OO15With the construction of the underwater detection apparatus, the velocity vector accurately calculated can be used so that the observation incidence angle will he calculated with high precision.

100161A forth aspect of the present invention is to provide the underwater detection apparatus in which the echo signal analysis unit of the third aspect estimates the kind of a target to be detected by using the target strength of an echo signal determined based on the amplitude of the echo signal and the observation incidence angle.

[0017]With the construction of the underwater detection apparatus, the observation incidence angle calculated with high precision can be used so that the kind of a target to be detected wUl be accurately estimated.

[0018]A fifth aspect of the present inventbn is to provide the underwater detection apparatus of the fIrst, second, third and fourth aspects in which an object to be detected is a single fish.

[0019$ sixth aspect of the present invention is to provide the underwater detection apparatus of the flfth aspect in which the echo signal analysis unit finds an echo signal from a single fish in echo signals from a school of fish based on echo signals supplied from the plurality of channels.

[OO2OjWith the construcfions of the underwater detection apparatus in the foregoing, there is shown a concrete embodiment of the invention for a singe fish as an object to be detected. Thus, there can be accurat&y calculated or estimated the velocity of a moving single fish or the kind of fish with the present invention.

[0021]A seventh aspect of the present invention is to provide an underwater detection method which comprises step for emitting simuftaneously ultrasounds into the water from a pluraifty of channels formed by dMding the transmissionreception surface of a transmitting and receiving device, and receiving echo signals generated in response to the uRrasounds, step for detecting an attitude of the center of the transmission-reception surface at a time instant when the echo signals received, in an absokite static coordinate system, and step for calculating from the echo signal the observation vector starflng at the transmitting and receiving device and ending at an object to be detected in a relative coordinate system and for converting the observation vector in the relative coordinate system to the corresponding observation vector in the absolute static coordinate system by using the conversion coefficient between the absolute static coordinate system and the reiative coordinate system obtained based on the attitude.

[OO22IAn eighth aspect of the present invention is to provide an underwater detection program for operating a computer to execute processes for calculating the observation vectors of an object to be detected, with the processes executed by the computer which comprises a process for emitting simultaneously ultrasounds into the water from a pluraty of channels formed by dividing the transmissionreception surface of a transmitting and receiving device, and receMng echo signals in response to the ultrasounds, a process for detecting an attitude of the center of the transmission-reception surface at a time instant the echo signals received, in an absolute static coordinate system, and a process for calculating from the echo signals the observation vector starting at the transmitting and receiving device and ending at an object to be detected in a relative coordinate system and for converting the observation vector in the relative coordinate system to a corresponding observation vector in the absolute static coordinate system by using the conversion coefficient between the absolute static coordinate system and the relative coorcflnate system obtained based on the attitude.

[0023]A ninth aspect of the present invention is to provide an underwater detection apparatus which comprises a transmitting and receiving device installed on a moving body for emitting an ultrasound signal and receiving an echo signal corresponding to the uftrasound signal, an attitude detection unft for detecting an attitude of the transmitting and receiving device at a reception time instant when the echo signal is received in the absolute static coordinate system, and an echo signal analysis unit for calculating from the echo signal an observation vector starting at the transmitting and receiving device and ending at an object to be detected in a relative coordinate system and for converting the observation vector in the relative coordinate system to a corresponding observation vector in the absolute static coordinate system by using the conversion coefficient between the absolute static coordinate system and the relative coordinate system obtained based on the attitude.

[0024]A tenth aspect of the present invention is to provide an underwater detection apparatus of the ninth aspect in which the attitude detection unit detects the attitude of the transmitting and receiving device based on signals transmitted by a plurality of the GPS satellites orbiting around the earth.

[0025]Further aspect of the present invention is to provide an underwater detection apparatus of the ninth aspect in which the transmitting and receiving device emits an FM chirp ultrasound signal into the water and receives a corresponding echo signal reflected by an object which will be pulsecompressed.

[0026]Without performing complicated transmission and reception controls, there can be obtained with high precision various detailed data relating to an object to be detected. For instance, there can be obtained the target strength of a single fish and the observation incidence angle with high precision so that the kind of fish can be more accurateiy determined.

B

BREF DESCRPTON OF THE DRAWNGS

(0027]Fig, 1 shows a block diagram ifiustrating the construction of an underwater detection apparatus according to an embodiment of the present invention; [O028Fig. 2 shows an explanatory drawing for calculating the velocity of a single moving fish and the incidence angle according to an embodiment of the present invention; [0029Fig. 3 shows the initial phase characteristics of the v&ocity of a moving object; 10030]Fig. 4 shows the initial phase characteristics of the observation incidence angle; and [0031]Fig. 5 shows a flow chart illusLrating observation processes according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0032]Hereinafter, there wiU be explained embodiments of an underwater detection apparatus, an underwater detection method and an underwater detection program according to the present invention referring to the Figures. Hg. 1 shows a block diagram of an underwater detection apparatus according to an embodiment of the present invention. Fig. 2 iflustrates an explanatory diagram for calculating the velocity of a single moving fish and the observation incidence angle according to an embodiment of the present invention.

[0033]An underwater detection apparatus 10 is comprised with an arithmetic processing unit 11, transmission and reception switching devices 121, 122, 123 and 124, a transmitting and receiving device 100, an attitude detection unit 20 and an indicator 30.

[0034]The arithmetic processing unit 11 is comprised with a transmission control unit 12, a reception unit 13, an echo signal analysis unit 14 and a display control unit 15. The transmission control unit 12 and the reception unit 13 are connected in paraUel to the transmission and reception switching devices 121, 122, 123 and 124, The reception unit 13 is connected to a single fish detection unit 14 and the display control unit 15. The display control unit 15 is connected to the indicator 30.

[0036]The attitude detection unit 20 is comprised with antennas 211 and 212, a sensor 22 and an attitude arithmetic unit 23, The antennas 211 and 212 receive positioning signals from positioning sateUites SAT such as GPS sateHites, perform correlation processing on the received signais and output resultant correlation-processed signals to the attitude arithmetic unit 23. The sensor 22 is comprised with an angular velocity sensor, an acceleration sensor and the like, and suppes signals representative of detected values to the attitude arithmetic unit 23. The athtude arithmetic unft 23 calcifiates an attitude angle of the ship having an underwater detection apparatus instaUed therein at a specific position of the ship 00 in the absokite static coordinate system with a known method by using the correlation process results and the detected values produced by the sensor.

More specificaUy, it calculates an attitude angle of the transmitting and receiving device in the absolute static coordinate system.

[0036jlt is to be noted that the absolute static coordinate system is, for instance, a coordinate system fixed to the globe. The X, Y and Z axes as shown in Fig. 2, are defined in such a way that mutually orthogonal two directions are in parallel with the horizontal plane with one of the two directions represented as the X axis and the other as the Y axis and that the other direction orthogonal to the horizontal plane is represented as the Z axis.

[0037]While, with the embodiments of the present invention, a relative coordinate system is defined. With the relative coordinate system, it is defined in such a way that mutually orthogonal two directions are in paraflel with the transmission-reception vibrating surface of the transmitting and receiving device 100, and that one of the two directions (for instance, fore-aft direction) is represented as the x axis and the other (starboard-port direction) is represented as the y axis and that the other direction orthogonal to the transmission-reception surface is represented as the z axis.

[0038The attitude of the transmitting and receiving device 100 in the absolute static coordinate system is determined by a yaw angle a formed between the xaxis rotatable around the Z-axis and the X-axis, a pitch angle formed between the z-axis rotatable

S

around the Y-axis and the Zaxis, and a ro ang y formed between the yaxis rotatable around the Xaxis and the Yaxis, [0039]The athtude detection unit 20 calculates atUtude angles as a yaw ange a, a pitch angle 13 and a rofl angle y at predetermined time intevals. It suppes the echo signal analysis unit 14 wfth the resultant atUtude angles together with the time instants at which the calculations were made. It is to be noted that the attitudes are calculated at time intervals shorter than transmission time intervals for emitfing respecfive ultrasound signals from the transmithng and receiving device 100, [0040]The transmitting and receiving device 100 is instaed, for instance, at the bottom of the ship in such a way that the transmissionrecepfion vibration surface thereof is maintained in paraflel with the horizontal plane when the ship is not swaying. The transmitting and receiving device 100 is divided into four parts having a zero4h channel represented as CHO, a first channel represented as CHI, a second channel as CH2, and a third channel as CH3. The four channels are formed as divided by mutuafly two orthogonal straight lines with the two lines intersected at the center of the transmission rec&ve surface of the transmitting and receiving devicelDO, [0041]For instance, the zero4h channel CHO and the first channel Cl-Il are disposed in the fore side with respect to the center of the transmission-receive surface of the transmitting and receiving devicelUO, While, the second channel CH2 and the third channel CH3 are disposed in the aft side with respect to the center thereof. The zero-th channel CHO and the third channel CHS are disposed in the port side with respect to the center of the transmission-receive surface of the transmitting and receiving devicelOO, while the first channel CHI and the second channel CH2 are disposed in the starboard side. The zero-th channel CHO is connected to the transmission and reception switching device 121. The first channel CHI is connected to the transmission and reception switching device 122.

The second channel CH2 is connected to the transmission and reception switching device 123. The third channel CH3 is connected to the transmission and reception switching device 124, [OO42JThe transmission control unit 12 generates transmission signals to emit ultrasounds from the transmitting and receiving device 100. The transmission signals have a carrier frequency in the ultrasonic wave frequency range such as, for instance, 38 KHz, The transmission signal contains an FM chirp signal the carrier frequency of which varies with time. The variable frequency range is, for instance, ± 2 KHz. The transmission signals are supplied to the transmitting and receiving device 100 through the transmission and reception switching devices 121, 122, 123 and 124.

[0043]The transmitting and receiving device 100 is excited by the transmission signals to emit ultrasounds for detecting objects into the water, The transmitting and receiving device synchronizes aU the channSs CHO through CR3 to emit ultrasound detection signals at the same time instant or simultaneously. The transmission control causes ultrasound detection signals to he emitted in a direction represented as z-axis orthogonal to the transmission-reception surface. Thus, the center axis of the directional characteristics of the transmission signal beam will coincide with the vertical direction.

[OO44jThe transmitting and receiving device 100 converts the echo signals reflected by a school of fish or a single fish "Fi" into electrical signals. The channels in the transmitting and receiving device 100 receive the echo signals respectively. The zero4h channel CR0 receives ultrasound echo signals and outputs the zero-th channel echo signals represented as ECH (0) to the reception unit 13 through the transmission and reception switching device 121. The first channel CR1 receives uftrasound echo signals and outputs the first channel echo signals represented as ECH (1) to the reception unit 13 through the transmission and reception switching device 122.

[0045]The second channel CR2 receives ultrasound echo signals and outputs the second channel echo signals represented as ECH (2) to the reception unit 13 through the transmission and reception switching device 123. The third channel CR3 receives ultrasound echo signals and outputs the second channel echo signals represented as ECH (3) to the reception unit 13 through the transmission and reception switching device 124. It is to be noted that hereinafter, there will be used channel echo signals ECH 1.0 represenfing a the four signals.

[0046]The reception unit 13 is comprised with, for instance, a matched fiRer, The reception unit 13 correlation-processes a repUca signal having the same waveform as the one of an ultrasound signal emitted by the transmitting and receiving device lao and the echo signals ECH from the respective channels, As a result, the reception unit 13 produces the respective pulsecompressed channel echo signals ECH. The use of the pulse compression will improve resolution in a depth direction or in a time direction. The recepflon unit 13 supplies the resultant pulse<ompressed channel echo signals to the single fish detection unit 14 and the display control unit 15.

[0047]lt is to be noted that the uftrasound signal is not Umited to the FM chirp signal, and that there can be used a pulse burst signal having a carrier frequency. In this case, the reception unit 13 does not need the construction of a matched filter and needs only an amplification process of the signals such as TVG.

[OO4BJThe echo signal analysis unit 14 detects a single fish based on echo signals from the respective channels. In order to detect a single fish, for instance, there is measured the width of a channel echo signal above a threshold level predetermined for detecting a target. If a measured width is narrower than a predetermined width for discriminating between a fish school and a single fish, it is determined that the channel echo signal has come from a single fish. The single fish is a target to be detected according to the present invention.

F004911he echo signal analysis unit 14 calculates the observation vector of a single fish in the absolute static coordinate system based on the channel echo signals corresponding to a single fish, although there will be provided detailed signal processes performed in the echo signal analysis unit 14 hereinafter, [0050]The echo signal analysis unit 14 calculates the v&ocity of a single moving fish based on observation vectors obtained at a plurality of time instants. The velocity of a single moving fish is the velocity vector used for the present invention.

[0051]The echo signal analysis unit 14 calculates an observation incidence angle of a

U

single fish based on the v&ocity of a movftig fish and observation vectors thereof obtained at a phiraUty of time instants.

[0052]The echo signal an&ysis unit 14 caictates the target strength TS of a single fish based on respective channel echo signals with a known method. The echo signal analysis unit 14 distinguishes and determines the kind of a single fish based on the relationship between the target strength TS and the observation incidence angle with a known method.

[0053]The echo signal analysis unit 14 supplies the analysis results to the display control unit 15. It is to be noted that the echo signal analysis unit 14 is required to select and supply to the display control unit 15 only relevant and necessary observation results from a plurality of the observation results.

0054]The echo signal analysis unit 14 obtains the observation vectors of a single fish in the absolute static coordinate system so that it is capable of performing arithmetic operations using a plurality of the observation vectors in the absolute static coordinate system in which there are no variations with time irrespective of fluctuations of the center axis of the directional characteristics of the transmitting and receiving device 100 at a plurality of time instants due to sway movements of the ship 90 or resultant movements of the transmitting and receiving device 100. It will suppress effects due to the movements against arithmetic operations using a plurality of the observation vectors. Thus, it wiU be possible to perform arithmetic operations using a plurality of the observation vectors accurately or at high precision. For instance, the foregoing embodiment of the invention is capable of accurately calculating the velocity vector and the observation incidence angle, and also of accurately determining the kind of fish.

[0055]The display control unit 15 generates fish detection display data based on the respective channel echo signals. The display control unit 15 combines desired display data generated based on the analysis results with the fish detection display data. The display control unit 15 supplies the combined display data to the indicator 30, The indicator 30 is comprised with, for instance, a liquid crystal display and displays the display data from the display control unit 15 on the screen thereof. 1.2

[0056]Refefflng to Hg. 2, the proces&ng performed by the echo &gnal analy&s unit 14 wW he specificay explained. ft is to be noted that in Fig. 2, Fi (0) represents a single fish corresponding to PING "O, and Fi (1) represents a single fish corresponding to PING "1".

xx represents an observation vector at a time instant an ultrasound signal PING "0" is emitted in the retive coordinate system. XX represents an observation vector at a time instant an ultrasound signal PING "0" is emitted in the absolute static coordinate system.

xx represents an observation vector in the relative coordinate system at a time an ultrasound signal corresponding to PING "O" is reflected by a single fish. XX0 represents an observation vector in the absolute static coordinate system at a time an ultrasound signal corresponding to PING "0" is reflected by the single fish, XXQr represents an observation vector in the relative coordinate system at a time an ultrasound signal corresponding to PING "0" is received by the transmitting and receiving device. XX0r represents an observation vector in the absolute static coordinate system at a time an uftrasound signal corresponding to P1NG "0" is received by the transmitting and receiving device.

[0057]xx represents an observation vector at a time instant an ultrasound signal PING "1' is emitted in the relative coordinate system. XX1 represents an observation vector at a time instant an ultrasound signal PING "1" is emitted in the absolute static coordinate system. xx1 represents an observation vector in the relative coordinate system at a time an ultrasound signal corresponding to PING "1" is reflected by the single fish. XX1 represents an observation vector in the absolute static coordinate system at a time an ultrasound signal corresponding to PING 1' is reflected by the single fish. xxlr represents an observation vector in the relative coordinate system at a time an ultrasound signal corresponding to PING "i" is received by the transmitting and receiving device. XX11 represents an observation vector in the absolute static coordinate system at a time an ultrasound signal corresponding to PING 1" is received by the transmitting and receiving device. V\/01 represents a velocity vector, and G represents an observation incidence angle.

0058]The echo signal analysis unit 14 calculates the observation vector of a single fish in the relative coordinate system based on the respective channel echo signals corresponding to echoes from the single fish.

[0059]As explained in the foregoing, the zero4h channel CHO and the first channel CHI are disposed in the fore side with respect to the center of the transmission-receive surface of the transmithng and receiving deviceloO, WMe, the second channel CH2 and the third channel CH3 are disposed in the aft side with respect to the center thereof, In the case in which the zeroth channel CHO and the third channel CH3 are disposed in the port side and the first channel CHI and the second channel CH2 are disposed in the starboard side, the observation vector of a single fish is calculated in the relative coordinate system as in the following.

[0060]The echo signal anaysis unit 14 adds the zeroth channel echo signals received by the zero-th channel CHO and the first channel echo signals received by the first channel CHI to receive echo signals from the fore area with respect to the transmuting and receiving device 100. The echo signal analysis unit 14 adds the second channel echo signals received by the second channel CH2 and the third channel echo signals received by the third channel CH3 to receive echo s?gnals from the aft area with respect to the transmitting and receiving device, [0061]The echo signal analysis unit 14 calculates the incoming direction (bearing) of a single fish echo projected to the vertical plane imaginary formed through an imaginary straight line in the bow-stern direction of the ship based on a phase difference or a time difference between the echo signal from the fore area and the echo signal from the aft area. The echo signal analysis unit 14 calculates a distance between the transmitting and receiving device 100 and the single fish projected to the vertical plane imaginary formed through an imaginary straight line in the bowstern direction of the ship based on time differences between the time instant ultrasounds transmitted and the time instants at which the echo signals are received from the fore and aft areas respectively.

[0062]The echo signal analysis unit 14 adds the zero4h channel echo signals and the third chann& echo signals to receive echo signals from the port area with respect to the transmitting and receiving device 100. The echo signal analysis unft 14 adds the first channel echo signals and the second channel echo signals to receive echo signals from the starboard area with respect to the transmithng and receiving device.

[0063]The echo signal analysis unit 14 calculates the incoming direction (bearing) of a single fish echo projected to the vertical plane imaginary formed through an imaginary straight line in the starboard-port direction of the ship based en a phase difference or a-time difference between the echo signal from the port area and the echo signal from the starboard area. The echo signal analysis unit 14 calculates a distance between the transmitting and receiving device 100 and a single fish projected to the vertical plane imaginary formed through an imaginary straight line in the starboard-port direction of the ship based on time differences between the time instant ultrasounds transmitted and the time instants at which the echo signals are received from the port and starboard areas respectively.

[0064]The echo signal analysis unit 14 calculates the bearing and the distance of the single fish with respect to the transmitting and receiving device 100 in the three--dimensional relative coordinate system based on the bearing and the distance obtained in the bowstern direction of the ship and the bearing and the distance obtained in the starboard-port direction of the ship.

[0065]The echo signal analysis unit 14 calculates an observation vector xx with respect to the center of the transmissionreception surface of the transmitting and receiving device 100. Here, 1" represents an integer number of the PING. The echo signal analysis unit 14 calculates at east an observation vector xxjrata time instant an echo signal is received.

[0066]The echo signal analysis unit 14 determines a coordinate conversion matrix Al based on an attitude angles (yaw angle a, pitch angle and roll angle y) supplied from the attitude angle detection unit 20. The coordinate conversion matrix Al is determined by using the attitude angles obtained at a time instant a predetermined conversion process from the relative coordinate system to the absolute static coordinate system is performed.

[0067]The coordinate conversion matrix Ai is represented by the foHowing equation 1, [0068] Equation 1: "All AU AU AL = A21 A22 A23 A31 A32 A33 [0069]lt is to be noted that the &ements in the matrix are represented respectively as in the foUowkig equation 2.

[0070] Equatbn 2: Al I = cos a1 cos ft A12 = cosct: sinft siny sin a1 cosy1 Al 3 = COS a1 511) [3 cos 4 sin a, siny1 A21 = Sin CX; COS i22 = sin a sin ft ± cos CX, A23 sin a sin ft cos -cos a1 sin y A31 = -siuft A32 = cosft siny1 A33 zn cosft cosy [0071]The echo signal analysis uniL 14 converts an observation vector XXirfl the reative coordinate system to a coFresponding observation vector XX in the absolute static coordinate system. More speciticaUy, the echo signal anaysis unit 14 determines a coorthnate conversion matrix A, and conducts a coordinate conversion process to obtain the observation vector by using the following conversion equation 3.

F0072] Equation 3: XX*jç X. [0073]The echo signal analysis unit 14 calculates a velocity vector based on observation vectors obtained at a plurality of time instants. For instance, the echo signal analysis unit 1.6 14 calculates to produce a velocity vector VV in the absolute static coordinate system based on an observation vector XX i and an observation vector XXjr corresponding respecUv&y to an emitted ultrasound PING 0 1) and another emitted ultrasound PING (i) which are adjacent with each other on a time axis. The equation therefor is as in the foflowing equation 4. "T" represents a transmission period of ifitrasounds which is the time interval of the respective ultrasound transmissions PING in accordance with the reference time.

[00741 Equation 4: (xx-xx. .) \T\i = [0075]For instance, with the example shown in Fig. 2, the velocity vector or the velocfty vector of a single moving fish vVi is obtained from the foHowing equation 5.

[0076] Equation 5: (ILIXX)

T

[0O77jAs explained in the foregoing, observation vectors obtained at a purality of time instants which will determine a velocity vector belong to the same absolute static coordinate system irrespective of influences due to sway amounts different from one another at a plurality of reception time instants. Thus, it is not influenced by amounts of the ships sway varied with time so that the velocity vector will be accurately calculated.

[0078]The echo sign& analysis unit 14 calculates the observation inddence angle G from the foflowing equation $ by using the calculated velocity vector VVi and the observation vector XX obtained at a time instant an ultrasound signal is reflected by a singie fish.

[0079] Equation 6: ( i_ti It V V1i.1 OdICCOS [0080]Supposing that the observation vector XXfr obtained at a reception time instant and the observation vector XX obtained at a time instant of uftrasound reflection are approximat&y the same, the observation vector XXr may be used as an alternative of the observation vector XX, It is also possible to more accurately calculate to obtain the vector with the folbwing method, [00B1]Designating the reception time instant as tr and the reflection time instant as t, the observaUon vector XX at a reflection time instant can be represented as in the foUowing equation.

[0082] XXis = XXirWKF.1) (tt) Suppo&ng that the propagation speed of an ultrasound signal and echo signals in the water is "C", the reflection time instant t can be approximated in accordance with the foUowing equation.

[0083] ttr (R /C) "RV represents a distance between the center of the transmitting and receiving device 100 and a single fish at a reception time instant. If a coordinate of the single fish is represented as (XE, Yr, Z) in the absolute static coordinate system, the distance is obtained from the foflowing equation 7. It is to be noted that the coordinate can be calculated from the observation vector XXjr.

[0084] Equation 7: 2

R

[0085]With the embodiment of the present invention, the v&ocity vector calculated with high precision is used so that the observation incidence angle wiH be accurately cculated.

[0086]The echo signal analyS unit 14 caiculates wfth a known method the target strength TS of the single fish based on the respective channel echo signals. It has been known that the relationship between the target strength TS and the observation incidence angle is different depending on kinds of fish. The r&ationship of each kind of fish has its own feature. Thus, the echo signal analysis urit 14 determines a kind of fish by comparing the rSationship between the target strength TS and the observation incidence angle calculated with the target strength TS and the observation incidence angle having been obtned for each kind of fish.

[OO87JWith this embodiment of the invention, there wifi be used an observation incidence angle calculated with high precision so that the kind of fish can be distinguished and accurately determined.

[0088]Fig, 3 shows initial phase characteristics of the velocity of a single moving fish. In Fig. 3, the horizontal axis represents the initial phases, and the vertical axis represents the velocity of a moving fish. As shown along the horizontal axis, it is said that the varying phase is equivalent in its meaning to emitting uftrasounds having the same phase in a situation in which the ship is swaying. In other words, the horizontal axis corresponds to sway amounts which are different depending on positions of the horizontal axis when the ship sways. A solid line shown in Fig. 3 corresponds to a case in which the construction according to the present invention is used, and a doffed line corresponds to a comparison case, and a dashed line corresponds to the reference case. The comparison case does not make corrections for swaying movements. The reference case does not have sways and not to make corrections against sways.

[0089]As shown in Fig. 3, with the comparison case, the velocity of a singk moving fish is varied depending on different amounts of the sway. However, when the construction of the embodiment according to the invention is used, the velocity of a moving fish wifl be maintained at a constant value irrespective of sways, and a value having approximately the same value can be obtained as compared with the case having no sways.

(0090]Fig, 4 shows the initial phase characteristics of an observation hicidence angle. In Fig. 4, the horizontal axis represents the initial phases, and the vertical axis represents the observation incidence angle. The horizontal axis in Fig. 4 is the same as the one in Fig. 3.

A soUd line shown in Fig. 4 corresponds to a case in which the construction according to the present invention is used, and a dotted line corresponds to a comparison case, and a dashed Une corresponds to the reference case. The comparison case does not make corrections for swaying movements. The reference case does not have sways and not to make corrections against sways, [O091]As shown in Fig4. with the comparison case, the observation incidence angle is varied depending on different amounts of the sway. However, when the construction of the embodiment according to the invention is used, the observation incidence angle will be maintained at a constant value irrespective of sways, and a value having approximately the same value can be obtained as compared with the case having no sways.

[0092]lt is to be noted that although, with the foregoing embodiment of the invention explained, the arithmetic processing to obtain the observation vector, the velocity vector and the observation incidence angle is conducted in the attitude detection unit 20 and the echo signal analysis unit 14, it is also possible to have another arrangement to achieve the same abject in such a way that a program for performing the same analysis processing has been stored in a memory in advance and is read therefrom and executed by an arithmetic device comprised with, for instance, a central processing unit.

[0093n this case, the observation processing should be conducted in accordance wfth the following flow chart. Fig. 6 shows a flow chart for performing the observation processing according to an embodiment of the present invention.

[0094]At first, the underwater detection apparatus 10 emits an ultrasound into the water and receives resultant echo signals through the four channels respectively (Slol).

[0095]Next, the underwater detection apparatus 10 calculates the observation vector XXr on the respective channel echo signals (5102). This processing is conducted each time an ultrasound signal or a PING is emitted.

[0096]Next, the underwater detection apparatus 10 derives attitude angles at a reception time instant at which the observation vector XXr is calculated and detemiines a coordinate conversion matrixA11 (8103).

[00$flNext, the underwater detection apparatus 10 converts the observation vector XX1in the relative coordinate system by using the coordinate conversion matrix A1 to calculate the observation vector XXII in the absolute static coordinate system (S 104).

[0098]Next, the underwater detection apparatus 10 calcuiates the velocity vector W1111 based on the observation vectors XXft, XXci...r obtained at the corresponding time instants respectively (5105).

[0099]Next, the underwater detection apparatus 10 calculates the observation incidence angie 0 based on the observation vectors XX1 and the velocity vector W 1)r (SI 06).

[0100]lt is to be noted that although there has been explained a single fish as an object in the water, as an example, is detected in the foregoing description, the foregoing construction can also be applied to such an environment in which the transmitting and receiving device for ernttting ultrasounds sways, and a target, paftcularly, as a moving target is detected therein, and is capable of performing the same operation and obtaining the same effects.

[OiOliAlthough there are used PINGs adjacent to each other on the time axis in the foregoing description, the invention should not be limhed to the foregoing embodiment thereof. It is also possible to calculate the velocity vector based on the observaLion vectors corresponding to PINGs which are not adjacent with each other on the time axis.

[0102]Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, a is to be noted that various changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims.

Claims

What is claimed is: 1. An underwater detection apparatus comprising: a transmitting and receiving device having the transmissionreception surface dMded to form a pluraflty of channels for emitting simultaneously an uftrasound signa from the respective channels into the water and receiving an echo signa' in response to the ultrasound signal; an attitude detection unit for detecting an attitude of the transmitting and receiving device at a reception time instant when the echo signal received in the absoute static coordinate system; and an echo signal analysis unit for calctating from the echo signal the observation vector starting at the transmitting and receiving device and ending at an object to be detected in a relative coordinate system and for converting the observation vector in the r&ative coordinate system to a corresponding observation vector in the absolute static coordinate system by using the conversion coefficient between the absolute static coordinate system and the relative coordinate system obtained based on the attitude.
2. The underwater detection apparatus of claim 1 wherein the echo signal analysis unit obtains the observation vectors of a target to be detected at a plurality of time instants in the absolute static coordinate system, and calculates the velocity vector based on the observation vectors obtained at the pluraity of time instants in the absolute static coordinate system.
3. The underwater detection apparatus of claim 2 wherein the echo signal anaysis unit calculates the observation incidence angle of the target to be detected based on the observation vectors arid the velocity vector in the absolute static coordinate system.
4. The underwater detection apparatus of claim 3 wherein the echo signal analysis unit estimates the kind of a target object to be detected by using the target strength of the echo signal determined based on the amplitude of the echo signal and the observation incidence angle.
5. The underwater detection apparatus of one of the claims 1 through 4 wherein the target Object to be detected is a single fish.
6, The underwater detection apparatus of the claim 5 wherein the echo signal analysis unft distinguishes an echo signal of the single fish from echo signals from a school of fish by using the echo sign&s supped from the pluraty of channels.
7. An underwater detection method comprising: step for emitting simultaneously uftrasounds into the water from a pluraUty of channels formed by dividing the transmission-reception surface of a transmitting and receiving device, and receiving echo signals generated in response to the ultrasounds; step for detecting an attitude of the center of the transmission-reception surface at a time instant when the echo signals received. in an absolute static coordinate system; and step for cSculating from the echo signal the observation vector starting at the transmitting and receiving device and ending at an object to be detected in a relative coordinate system and for converting the observation vector in the relative coordinate system to the corresponding observation vector in the absoluLe static coordinate system by using the conversion coefficient between the absolute static coordinate system and the r&ative coordinate system obtained based on the attitude.
8. An underwater detection program for operating a computer to execute processes for calculating the observation vectors of an object to be detected, with the processes executed by the computer comprising: a process for emitting simultaneously ultrasounds into the water from a pluraUty of channels formed by dividing the transmission-reception surface of a transmitting and receiving device, and receiving echo signals in response to the ultrasounds; a process for detecting an attitude of the center of the transmissionreception surface at a time instant the echo signals received, in an absolute static coordinate system; and a process for calculating from the echo signals the observation vector starting at the transmitting and receiving device and ending at an object to be detected in a relative coordinate system and for converting the observation vector in the r&ative coordinate system to a corresponding observation vector in the absolute static coordinate system by using the conversion coefficient between the absolute static coordinate system and the relative coordinate system obtained based on the attitude.
9. An underwater detection apparatus comprising: a transmitting and receiving device installed on a moving body for emithng an ultrasound signai and receiving an echo signal corresponding to the ultrasound signal; an affitude detection unit for detecting an attitude of the transrnthing and receiving device at a reception time instant when the echo signal is received in the absolute static coordinate system; and an echo signal analysis unit for calculating from the echo signal an observation vector staffing at the transmitting and receiving device and ending at an object to be detected in a relative coordinate system and for converting the observation vector in the reative coordinate system to a corresponding observation vector in the absolute static coordinate system by using the conversion coefficient between the absolute static coordinate system and the relative coordinate system obtained based on the attitude.
10. The underwater detection apparatus of the claim 9 wherein the attitude detection unit detects the attitude of the transmitting and receiving device based on signals received from a plurality of the OPS satelhtes orbiting around the earth.
11. The underwater detection apparatus of the claim 9 wherein the transmitting and receiving device emits an FM chirp ultrasound signal into the water and receives a corresponding echo signal reflected by an object which will be pulse-compressed.
12. An underwater detection apparatus substantially as described herein with reference to and as illustrated in the accompanying drawings.
13. An underwater detection method substantially as described herein with reference to the accompanying drawings.