JP2007064768A - Underwater detection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an underwater detection system capable of indicating detected information added with velocity information of an echo reflector on a display screen. <P>SOLUTION: The underwater detection system transmitting ultrasonic wave underwater, receiving reflection echo from an object and indicating is provided with a filter processing section for filtering reception signal by using a band-pass filter having a stopband at a part of the passing band frequency. The stopband is made a frequency band of signal reflected by a target with zero moving velocity. By this, reflection echo from sea bottom and a plankton layer is removed and only reflection echo from a school of fish moving with a velocity can be indicated on the display screen. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an underwater detection apparatus that transmits ultrasonic waves in water and receives and displays reflected echoes from an object.

2. Description of the Related Art Conventionally, an ultrasonic underwater detection device such as a fish finder or a scanning sonar that transmits ultrasonic waves in water and receives and displays reflected echoes from an object is known. As an example of this, there is one described in Patent Document 1, for example.

Patent Document 1 discloses a technique for obtaining a signal with a high S / N ratio by determining optimum filter characteristics corresponding to the number of independent beams for each direction based on the moving speed and moving direction of a moving body. Details of this Patent Document 1 will be described below.

FIG. 9 is a block diagram showing the configuration of the underwater detection device described in Patent Document 1. As shown in FIG.

As shown in FIG. 9, the conventional underwater detection device includes a transducer 101, a transmission unit 102, a transmission / reception switching unit 103, a fixed band filter 104, an amplifier / mixer 105, a fixed band filter 106, and an amplifier. 107, an A / D converter 108, a beam forming unit 109, an automatic band control unit 110, a control unit 111, a speed sensor / direction sensor 112, and a detection unit 113.

The transmitter / receiver 101 converts the transmission electric signal from the transmission unit 102 into a sound wave and transmits the sound wave, and converts an ultrasonic echo returned from the water into an electric signal when receiving the wave. The transmitter 102 is an electric signal generator for emitting a sound wave having a predetermined pulse width at a specified tilt angle (a sound wave emitting direction with respect to the sea surface), and supplies the generated signal to the transmitter / receiver 101. The transmission / reception switching unit 103 is a circuit that switches a signal path between transmission and reception. The transmission / reception switching unit 103 allows only a transmission signal to pass during transmission and allows only a reception signal to pass during reception.

The fixed band filter 104 is a first-stage fixed band filter provided in the receiving unit, and extracts a signal in a necessary frequency band from the received signal obtained from the echo received by the transmitter / receiver 101. It is a filter. The amplifier / mixer 105 amplifies and frequency-shifts the filtered received signal and converts it to an intermediate frequency. The fixed band filter 106 is a second-stage fixed band filter, and is a filter for further narrowing the frequency band by removing unnecessary sideband signals contained in the frequency-converted signal. The amplifier 107 amplifies the received signal up to the input level of the A / D converter 108 at the next stage.

The A / D converter 108 converts the amplified received signal into a digital signal. The beam forming unit 109 forms a beam by continuously scanning the received signal in the horizontal direction.

The automatic bandwidth control unit 110 detects the center frequency and bandwidth of each direction based on the speed information and the direction information obtained from the speed sensor / acceleration sensor 112, and based on these, the S / N ratio with the narrowed bandwidth is detected. It generates a high signal.

The control unit 111 is a controller composed of a CPU and a memory, and controls the operation of the automatic bandwidth control unit 110 together with the entire apparatus. The speed sensor / orientation sensor 112 is a sensor that detects the ship speed and the heading. The speed sensor may be a device such as a GPS or a tide meter, or a speed sensor attached to a hull or a transducer (for example, an acceleration sensor that integrates its output over time to obtain a speed). As the sensor, devices such as a GPS, a gyrocompass, and an electronic compass are conceivable.

The detector 113 detects an envelope of the signal generated by the automatic band controller 110, and outputs the detected envelope to a display device (not shown).

In the above configuration, the transmission unit 102 supplies a pulse signal having a predetermined frequency to the wave transmitter / receiver 101 as a transmission signal via the transmission / reception switching unit 103. The transducer 101 converts this signal into an ultrasonic wave and emits an ultrasonic beam into the water. The emitted ultrasonic waves are reflected by the seabed or underwater school of fish, and the echoes are received by the transducer 101. The received ultrasonic wave is converted into an electrical signal by the transducer 101, and this signal is output as a received signal.

In the processing of the received signal, first, as a pre-beam forming process, unnecessary noise included in the received signal is removed by the fixed band filter 104, and only a signal in a predetermined frequency band is extracted. The extracted signal is amplified and frequency shifted by the amplifier / mixer 105 and converted to an intermediate frequency. Thereafter, unnecessary sideband signals are removed by the fixed band filter 106, further amplified by the amplifier 107, and converted into a digital signal by the A / D converter 108. Note that the timing of A / D conversion is not limited to this.
The beam forming process is performed by the beam forming unit 109, and a beam of a reception signal is formed by continuous horizontal scanning and is output to the automatic band control unit 110.

Finally, as post-beam forming processing, the automatic band controller 110 detects the center frequency and bandwidth for each direction based on the speed information and the direction information obtained from the speed sensor / acceleration sensor 112, and based on these. Thus, a signal with a high S / N ratio with a narrow bandwidth is generated. The detection unit 113 detects a signal envelope from the signal generated by the automatic band control unit 110, and outputs the data to a subsequent display device. The display device displays an echo image representing underwater information such as the seabed and school of fish based on the data.

Here, the automatic bandwidth control unit 110 described in Patent Document 1 will be described in more detail with reference to FIG.
FIG. 10 is a block diagram showing a specific configuration of the automatic bandwidth control unit 110.
As shown in FIG. 10, the automatic bandwidth control unit 110 includes a frequency detection unit 201, a Doppler shift frequency estimation unit 202, a bandwidth estimation unit 203, multiplexers 204 and 205, a mixer 206, and a variable bandwidth filter 207. It consists of and.

The frequency detection unit 201 detects the center frequency and frequency dispersion of a signal in each horizontal direction (cross-sectional direction with respect to the cross-sectional mode) from the received signal using an autocorrelation method, a Fourier transform method, or the like. Note that the frequency dispersion represents the degree of spread of the frequency component of the signal, and although it is different from the bandwidth precisely, it may be considered to be proportional to the bandwidth.

The Doppler shift frequency estimation unit 202 is used when it is difficult for the frequency detection unit 201 to detect the Doppler shift frequency from the received signal. The Doppler shift frequency estimation unit 202 estimates and calculates the Doppler shift frequency of the entire horizontal circumference (the cross-sectional direction for the cross-sectional mode) that will be generated from the ship speed information obtained from the speed sensor. The heading is used to convert the east / west / north / south speed vector to the front / rear / right / left speed vector of the transducer when a Doppler sonar, tide meter, or GPS is used as a speed sensor. used. The bandwidth estimation unit 203 estimates the bandwidth of the received signal from the transmission pulse width information.

The MUXs 204 and 205 are both multiplexers, and use the information obtained from the received signal by the frequency detection unit 201, or the estimated values estimated based on the ship speed and the pulse width by the Doppler shift frequency estimation unit 202 and the bandwidth estimation unit 203 To choose whether to use.

When the center frequency is selected by the MUX 204, the mixer 206 shifts the center frequency of the received signal based on the selected center frequency to generate a baseband (DC) signal. The variable bandwidth filter 207 is a filter having the bandwidth selected by the MUX 205, and limits the bandwidth of the input baseband signal and removes frequency components other than the signal, thereby reducing the SN of the received signal. Improve.

As described above, in Patent Document 1, the automatic bandwidth control unit 110 performs bandwidth control of the reception signal for each direction, so that the reception frequency is based on various factors such as movement of the ship, sway of the hull, and tidal current. It is possible to ensure a high S / N ratio for each direction even when the shift is performed.
JP 2003-84060 A

However, in Patent Document 1 described above, the data output to the display device is merely a display of all the level information of the received signal. That is, in the conventional scanning sonar and fish finder, only the received signal level is detected and displayed regardless of the velocity information of the transmission signal reflecting object. Therefore, for example, it has been impossible to display only a desired school of fish that migrates in the water except the seabed and the like. In particular, when there is a shallow water area or plankton layer at a shallow water depth, fish echoes are superimposed on the sea floor reflections, sea surface reflections, and plankton reflection echoes, making it difficult to identify the fish school. In some cases, there is a problem that it becomes impossible to distinguish at all.

Moreover, in this patent document 1, since the filter process which has a filter characteristic with a narrow pass bandwidth is performed for the purpose of improving the S / N ratio, the movement having a speed range relatively equivalent to the moving speed of the ship Only the received echo of the object is passed. For this reason, with regard to moving objects that have a moving speed relatively higher than the moving speed of the ship, such as fish species such as carp and salmon, the Doppler shift frequency generated according to the moving speed of the fish type is the filter characteristic. Out of the passband, the signal components are attenuated by the filter process and are not displayed. As a result, in Patent Document 1, there is a possibility that a detection failure of a moving object having a moving speed relatively higher than the moving speed of the own ship may occur.

The present invention has been made in view of such a problem, and displays not only level information of a signal received from an underwater reflecting object but also detection information on the display screen in consideration of speed information of the echo reflecting object. It is an object of the present invention to provide an underwater detection device capable of performing the above.

In order to solve the above problems, the present invention generates a desired filter coefficient by frequency-shifting a filter coefficient corresponding to a predetermined target speed range according to the moving speed and moving direction of a moving object such as a ship. And a filter processing unit that performs filtering of the received signal using the filter coefficient generated by the band limitation calculation unit. As a result, it is possible to display on the display screen only the reflected echoes from the target included in the constant speed range corresponding to the filter coefficient corresponding to the predetermined target speed range.

In the present invention, the band limit calculation unit generates a bandpass filter having a stopband as a part of the passband frequency, and includes the frequency of the signal reflected by the target whose movement speed is zero in the stopband. It is characterized by a band. As a result, reflected echoes from targets that do not have velocity such as the seabed or plankton layer are removed, and only reflected echoes from targets that move at a constant velocity, such as school of fish, are displayed on the display screen. It becomes possible.

Further, the present invention provides a predetermined target speed based on the moving speed and moving direction of a moving body such as a ship, or based on the average frequency for each direction obtained by the complex autocorrelation method by the band limit calculating unit. A filter coefficient having a range is frequency-shifted for each azimuth to generate independent filter coefficients for each azimuth from one filter coefficient. Accordingly, even in an apparatus such as a scanning sonar that transmits a plurality of beams at a constant elevation angle in the entire circumferential direction, it is possible to perform an appropriate filtering process for each beam direction.

Further, according to the present invention, the band limiting calculation unit updates the filter coefficient in real time even during the reception section in accordance with a speed change, a course change, or a change caused by shaking of a moving body such as a ship, and the filter The processing unit performs a filtering process based on the changed filter coefficient. As a result, the received signal can be processed in real time.

Further, according to the present invention, the filter processing unit filters the same received signal using a filter coefficient having a predetermined bandwidth and a filter coefficient generated by the band limit calculation unit, respectively. The filtering result is simultaneously displayed on the display screen. Thereby, the user can compare the filtering results using different filter coefficients on the display screen. For example, when the filter coefficient that cuts the echo from the sea floor is generated by the band limit calculation unit, the user can output the image of the filtering result using the conventional filter coefficient for displaying the sea floor and the video of the sea floor or the like. It becomes possible to simultaneously view the image of the filtering result using the filter coefficient of the present invention in which is deleted.

In addition, the present invention is characterized by further comprising a motion correction function capable of correcting motion of a moving body such as a ship and transmitting and receiving ultrasonic waves in water. This makes it possible to perform an accurate ultrasonic signal transmission / reception process.

In addition, the present invention is characterized in that the Doppler shift amount of the received signal is displayed as data for each color in accordance with the magnitude of the frequency. Thereby, the user can intuitively grasp the moving speed of the target such as a school of fish from the display screen.

According to the present invention, it is possible to remove reflected echoes from the seabed and plankton layer and display only reflected echoes from a school of fish moving at a constant speed on the display screen. Therefore, it contributes to the improvement of fishery efficiency at the time of fish school search / fish school tracking without being influenced by the weather and fishing ground conditions. In addition, by improving the ability to identify the school of fish buried in the seafloor echo and plankton layer, it will provide clear images to the user and contribute to the improvement of fishery efficiency. In particular, according to the present invention, since only the bottomed fish school buried in the seabed can be displayed on the display screen, for example, in the real target lock process which is one function of the conventional scanning sonar, the influence of the seabed echo This makes it possible to track a school of fish buried in a seafloor echo that could not be tracked in the past. Further, when applied to the scanning sonar cross-sectional mode, it is possible to suppress the sea bottom echo, which has been a conventional concern, or to remove the sea bottom echo.

In addition, as a display form of the received echo using the technology according to the present invention, by providing a comparison image with the conventional display screen, it is possible to further distinguish the seafloor echo, the plankton layer and the fish echo having the velocity. Can do.

Furthermore, according to the present invention, since only a target having a predetermined speed can be detected, it is also possible to remotely monitor and grasp the position of an object entering from underwater or a diver working in water. .

(Embodiment 1)
Hereinafter, an underwater detection device according to Embodiment 1 of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an example of the configuration of an underwater detection device according to Embodiment 1 of the present invention.
In FIG. 1, an underwater detection device according to the present invention includes a front end interface 1, a transmission beam forming unit 2, a beam forming preprocessing unit 3, a receiving beam forming unit 4, a band limit calculation unit 5, and a filter process. The unit 6 and the display processing unit 7 are configured.

The front end interface 1 is a transmission / reception switching unit, transfers a transmission code output from the transmission beam forming unit 2 to a transmitter / receiver (not shown) as a front end unit, and receives a reception signal output from the front end unit Is transferred to the beam forming pre-processing unit 3. The transmission beam forming unit 2 generates transmission waveform time-series data for each channel in order to form a transmission beam. For example, in the scanning sonar, the transmission beam forming unit 2 generates data for emitting a sound wave having a predetermined pulse width at a specified tilt angle. Although not shown here, an accurate ultrasonic signal transmission / reception process is performed by providing a vibration correction function capable of transmitting / receiving ultrasonic waves in water by correcting the vibration of a moving body such as a ship. It becomes possible.

The beam forming preprocessing unit 3 performs filter processing for noise removal, gain correction processing represented by TVG (Time Variable Gain) necessary for beam forming, and the like, and outputs data to the reception beam forming unit 4.

The reception beam forming unit 4 forms a reception beam by performing multi-beam forming processing by a phase synthesis method on the reception signal. Beam formation can also be performed by continuously scanning the received signal in the horizontal direction.

The band limitation calculation unit 5 holds a filter coefficient corresponding to a predetermined target velocity range in a storage unit such as a memory in advance. Here, the predetermined target speed range is a speed range determined based on the speed of the target to be detected. The filter coefficient corresponding to a predetermined target speed range has a filter characteristic having a passband frequency that passes only a reflected echo from a target moving at a predetermined speed when the speed of the moving body (own ship) is zero. Is a filter coefficient. The band limitation calculation unit 5 acquires a filter coefficient corresponding to the predetermined target speed range from the storage unit, and has a desired filter characteristic considering the target speed range according to the moving speed of the moving body. Generate coefficients.

For example, in an apparatus such as a scanning sonar that scans in the entire circumferential direction, when the ship moves, the Doppler shift amount differs for each beam direction. Therefore, the band limit calculation unit 5 shifts the frequency of the filter coefficient obtained for each beam azimuth based on the moving speed and moving direction of the moving object or based on the average frequency for each azimuth obtained by the complex autocorrelation method. To do. Thereby, the band limitation calculation unit 5 can generate independent filter coefficients for each beam direction. The filter coefficient generated in this way is, for example, a filter in which a reflected echo from a target near zero speed is a stop band and only a reflected echo from a target moving at a speed within a predetermined range is a pass frequency band. Has characteristics.

The filter processing unit 6 performs filtering of the received signal of each beam using the filter coefficient generated for each direction by the band limitation calculation unit 5. As a result, the filtered data is only reflected echoes from targets that move at a predetermined range of speed, such as reflected echoes from the seabed and reflected echoes from plankton layers that have almost no velocity. It becomes.

The display processing unit 7 performs a process for displaying the data after the filtering process on the display screen. That is, the signal for each azimuth filtered by the filter processing unit 6 is detected, TVG processing, interpolation processing, and the like are performed, and data corresponding to the display form of the echo video is output to an instruction device (not shown). The pointing device displays an echo video representing the underwater information based on the data output from the display processing unit 7. As a display form of the echo video, not only the signal intensity of the received signal but also the Doppler shift amount of the received signal may be displayed by data for each color according to the frequency. Thereby, the user can intuitively grasp the moving speed of the target such as a school of fish from the display screen.

Next, the operation of the underwater detection device of the present invention will be described.

In the above-described configuration, the transmission beam forming unit 2 supplies a pulse signal having a predetermined frequency as a transmission signal to a transmitter / receiver (not shown) via the front end interface 1. The transducer converts this signal into ultrasound and launches an ultrasound beam into the water. The emitted ultrasonic waves are reflected by the seabed and underwater fish schools, and the echoes are received by the transducer. The received ultrasonic wave is converted into an electrical signal by a transducer, and this signal is output as a received signal to the beam forming preprocessing unit 3 via the front end interface 1.

As for the processing of the received signal, first, as beam forming preprocessing, the beam forming preprocessing unit 3 performs filter processing for noise removal, gain correction processing represented by TVG (Time Variable Gain) necessary for beam forming, and the like. Done.

The beam forming process is performed by the reception beam forming unit 4, and a received beam is formed by performing a multi-beam forming process using a phase synthesis method on the received signal.

Next, in post-beamforming processing, the band limitation calculation unit 5 generates filter coefficients having filter characteristics for detecting only a target moving at a predetermined speed for each beam direction. The filter coefficient generated by the band limit calculation unit 5 is updated in real time even during the reception period in accordance with a change in the speed of the moving body, a change in the course, or a fluctuation.

The filter processing unit 6 performs filtering of the received signal for each beam azimuth using the filter coefficient generated by the band limitation calculation unit 5.

Finally, the display processing unit 7 detects a signal envelope from the received signal after the filter processing, performs TVG processing, interpolation processing, and the like, and outputs the data to a subsequent instruction device. The pointing device displays an echo video representing the underwater information based on the data.

Next, the band limitation calculation unit 5 which is a characteristic part of the present invention will be described in more detail.
FIG. 2 is a diagram illustrating a specific configuration of the band limitation calculation unit 5. Here, a case where the echo transmission / reception mode is the CW mode will be described.
In FIG. 2, the band limitation calculation unit 5 includes a frequency shift unit 21, a frequency detection unit 22, and a filter coefficient calculation unit 23.

The frequency shift unit 21 shifts the reception band to DC (baseband) by performing frequency shift corresponding to the deviation according to the AD sampling frequency setting value with respect to the distance direction sampling data for each direction according to the number of input beams. .

The frequency detection unit 22 uses the autocorrelation method, the Fourier transform method, or the like, from the received signal in the horizontal all-around direction (the cross-sectional direction for the cross-sectional mode, and the elevation / elevation-angle direction for each direction for the arbitrary elevation / elevation cross-sectional mode) ) To detect the center frequency of the signal. In this system, the complex autocorrelation method is used to analyze the frequency of the entire circumference in real time. This complex autocorrelation method is a process of calculating a complex autocorrelation value at a certain time lag from the correlation calculation start distance after transmission is completed for each beam azimuth to obtain an average frequency and frequency dispersion.

The frequency detection unit 22 replaces the processing contents described above or selectively based on the ship speed and true course information acquired from the outside for every circumferential direction corresponding to the ship speed (in the cross-sectional mode, a vertical beam). The center frequency for each direction may be calculated.

Next, the filter coefficient calculation unit 23 performs the following processes (1) to (4).

(1) The filter coefficient calculation unit 23 acquires a filter coefficient having filter characteristics corresponding to a speed range to be detected in advance. This filter coefficient is held in storage means such as a memory. For example, a filter coefficient having a filter characteristic corresponding to a specific target velocity range is selected by a user's selection. FIG. 3 is a diagram illustrating an example of the filter coefficient acquired by the filter coefficient calculation unit 23. Here, the filter coefficient calculation unit 23 acquires a low-pass filter having a bandwidth corresponding to a certain target velocity range as shown in FIG.

(2) Next, the filter coefficient calculation unit 23 calculates the passband center frequency of the acquired filter coefficient for each beam direction based on the average frequency for each circumferential direction obtained by the complex autocorrelation method by the frequency detection unit 22. The frequency shift is performed for each vertical beam azimuth in the section mode and for each beam elevation angle corresponding to the arbitrary elevation angle section in the arbitrary elevation angle section mode. Thus, filter coefficients having different filter characteristics corresponding to the number of independent beams for each direction are generated from one filter coefficient. Of course, the frequency detector 22 shifts the frequency of the filter coefficient obtained on the basis of ship speed and true course information input from the outside, instead of the average frequency for each circumferential direction obtained by the complex autocorrelation method by the frequency detection unit 22. May be.

FIG. 4 shows filter coefficients for a specific beam orientation after the processing of (2). The filter coefficient calculation unit 23 obtains a bandpass filter as shown in FIG. 4 by performing frequency shift on the filter coefficient acquired in (1).

(3) For the filter coefficient generated in (2), the filter coefficient calculation unit 23 further increases the passband frequency component or the cut-off frequency component so that the received signal in the speed range to be detected in advance is detected. Shift frequency. As a result, it is possible to generate independent filter coefficients for each circumferential direction in which only a desired speed range is a passband frequency. As shown in FIG. 5, the filter coefficient generated by the frequency shift at this time has a stop band in a part of the passband frequency in which frequency folding is actively generated by performing frequency shift in the real number region. It is a bandpass filter.

In FIG. 5, the frequency of the velocity component 0 is a stop band of the generated bandpass filter. The stop band of the band pass filter is set so that at least the band includes a Doppler shift frequency generated only by the movement of the ship, that is, a frequency of a reflected echo from a target whose moving speed is zero. As a result, it is possible to remove reflected echo from a target that does not move, such as the seabed, by the stop band.

Further, the frequency of the negative velocity component on the left side shown in FIG. 5 is a passband frequency for detecting a reflected echo from a target moving at a predetermined speed in the same direction with respect to the moving direction of the ship. The frequency of the plus velocity component is a passband frequency for detecting a reflected echo from a target moving at a predetermined speed in a direction opposite to the moving direction of the ship. In this way, the band pass fill having a stop band in part can be realized by, for example, a combination of two band pass filters or a combination of a band pass filter and a notch filter.

(4) Finally, the filter coefficient generated in (3) is stored in the filter coefficient memory owned in the filter processing unit 6. In the above description of the band limiting operation unit 5, the case where the echo transmission / reception mode is the CW mode has been described. However, when the echo transmission / reception mode is the FM mode, the distance direction complex matched filter for each beam direction is used. The coefficients may be generated by the filter coefficient calculation unit 23. Therefore, in the FM mode, the frequency shift unit 21 and the frequency detection unit 22 do not function.

In the above description of (1) to (4), the band limit calculation unit 5 generates a band pass filter having a stop band in a part of the pass band frequency by positively generating frequency folding. Of course, the present invention is not limited to this. For example, a beam is prepared by preparing a band pass filter having a stop band in part in advance and shifting the frequency for each direction based on the speed of the ship. It is also possible to generate independent filter coefficients for each orientation.

Next, the characteristic of the filter coefficient generated by the underwater detection device of the present invention will be described with a specific example.
For example, in the scanning sonar, it is assumed that the transmission / reception frequency is transmitted at the same frequency f0 in the entire circumferential direction, and the ship is traveling straight at 5 kt. Further, the forward Doppler shift frequency generated in this case is assumed to be fd. At this time, whether it is a school of fish or the seabed, the forward reception frequency from an object that is not moving is f0 + fd. In the present invention, this f0 + fd frequency is detected in real time by the autocorrelation method or calculated from ship speed information and true course information supplied from an external device, the f0 + fd frequency is set as a stop band, and only a predetermined speed range is set as a passband frequency. A band pass filter to be generated is generated by the band limit calculation unit 5.

Thereafter, the filter processing unit 6 performs filtering of the received signal using a bandpass filter having this stop band. As a result, it is possible to erase reflection echoes from the seabed that is not moving, the plankton layer, or a stopped school of fish from the display screen.

On the other hand, when there is a school of fish moving forward at the speed α in the same direction as the movement of the ship, the Doppler shift frequency at the speed α is fd + fα. The reception frequency at this time is f0 + fd + fα. When f0 + fd + fα is included in the passband frequency of the bandpass filter having a stopband in a part generated by the band limitation calculation unit 5, the frequency band of f0 + fd is cut as described above, but the frequency band of fα The frequency component is output as a filtering result. For this reason, only the school of fish moving within a preset speed range is displayed on the display screen.

As described above, according to the underwater detection device according to Embodiment 1 of the present invention, a bandpass filter that generates only a reflected echo from a target moving within a predetermined speed range as a passing frequency band is generated. By filtering the received signal using a filter, reflected echoes from the seabed and plankton layer can be removed. At the same time, it is possible to display only reflected echoes from a school of fish moving with speed on the display screen. In particular, in the present invention, by appropriately controlling the filter band, it is possible to delete only small fish or the like that are slow in speed and display only carp and carp that migrate at high speed. For this reason, the so-called `` pecker '' such as a nearby ship, a long-distance ship, a sea-turning ship, etc., and a small fish, such as a salmon, and a fishing target, This makes it possible to distinguish salmon from a long distance and contribute to improving fishery efficiency.

(Embodiment 2)
Next, an underwater detection device according to Embodiment 2 of the present invention will be described.
The present invention can also be realized by configuring the automatic band control unit 110 of the conventional underwater detection device described with reference to FIG. 9 as shown in FIG.
FIG. 6 is a diagram illustrating a specific configuration of the automatic bandwidth control unit of the underwater detection device according to the second embodiment of the present invention.

In FIG. 6, the automatic bandwidth control unit includes a frequency detection unit 31, a Doppler shift frequency estimation unit 32, a bandwidth calculation unit 33, a MUX 34, a filter coefficient generation unit 35, a filter coefficient memory 36, and a variable bandwidth. And a filter 37.

The frequency detection unit 31 uses the autocorrelation method, the Fourier transform method, or the like, from the received signal in the horizontal all-around direction (the cross-sectional direction for the cross-sectional mode, and the elevation / elevation angle direction for each direction for the arbitrary elevation / elevation cross-sectional mode) ) To detect the center frequency of the signal. In this system, the complex autocorrelation method is used to perform frequency analysis of the entire circumference in real time.

The Doppler shift frequency estimation unit 32 is used when it is difficult for the frequency detection unit 31 to detect the Doppler shift frequency from the received signal. The Doppler shift frequency estimation unit 32 estimates and calculates the Doppler shift frequency of the entire horizontal circumference (cross-sectional direction for the cross-sectional mode) that will be generated from the ship speed information obtained from the speed sensor. The heading is used to convert the east / west / north / south speed vector to the front / rear / right / left speed vector of the transducer when a Doppler sonar, tide meter, or GPS is used as a speed sensor. used.

The bandwidth calculation unit 33 calculates a bandwidth corresponding to the speed range of the target based on the speed range of the target to be detected designated by the user or the like. The MUX 34 is a multiplexer, and selects whether to use information obtained from the received signal by the frequency detection unit 31 or to use an estimated value estimated based on the ship speed by the Doppler shift frequency estimation unit 32.

The filter coefficient generation unit 35 generates a filter coefficient corresponding to the speed range of the target based on the bandwidth corresponding to the speed range to be detected calculated by the bandwidth calculation unit 33. After that, the filter coefficient is frequency-shifted in each direction (cross-sectional direction for the cross-sectional mode, and elevation / elevation cross-sectional direction for each direction for the arbitrary elevation / elevation angle section mode) based on the center frequency selected by the MUX 34. Then, a band pass filter having a stop band in a part of the pass band frequency is generated. By this processing, a filter coefficient corresponding to the velocity range of an independent target is generated for each direction.

The filter coefficient memory 36 is a memory that stores the filter coefficient for each horizontal direction generated by the filter coefficient generation unit 35. The variable bandwidth filter 37 is a filter having a bandwidth based on the filter coefficient calculated by the filter coefficient generation unit 35, and restricts the band of the input signal or blocks only the designated band of the input signal.

With such a configuration, only a reflected echo from a target belonging to a desired speed range can be displayed by a simple design change of the automatic band control unit 110 of the conventional underwater detection device.

As described above, according to the underwater detection device according to Embodiment 2 of the present invention, the automatic band control unit generates the filter coefficient having the filter characteristics corresponding to the desired target velocity range for the entire circumferential direction, By filtering the received signal using the filter coefficient, similar to the underwater detection device according to the first embodiment, the reflected echoes from the seabed and plankton layer are removed, and the school of fish moving with speed, etc. It is possible to display only the reflected echo from the display screen.

(Embodiment 3)
Next, an underwater detection device according to Embodiment 3 of the present invention will be described.
The underwater detection device according to the third embodiment of the present invention uses a filter that takes into account the target velocity range described in the first or second embodiment, and a conventional filter having a predetermined passband frequency. The same received signal is filtered. Thereby, the filtering result using a different filter can be simultaneously displayed on a display screen. The conventional filter having the predetermined passband frequency is a bandpass filter having a fixed passband. For example, Patent Document 1 described in FIG. 9 and FIG. Filters generated from the described technique are possible.

7 and 8 are diagrams showing screen display examples of the underwater detection device of the present invention. FIG. 7 shows the result of an experiment conducted at a point with a water depth of about 170 m. From the bottom of the sea using an image (left side) obtained by cutting the reflected echo from the sea bottom using the filter according to the present invention and the conventional filter. The image (right side) which displayed the reflective echo of is shown. FIG. 8 shows the result of an experiment conducted at a point where the water depth is 600 m or more, and an image (left side) displaying a reflection echo from a plankton layer existing in the middle layer of about 100 m of the seabed using a conventional filter, The image (right side) which cut the reflective echo from a plankton layer using the filter concerning the present invention is shown. The filter according to the present invention is a band-pass filter having a predetermined speed range as a pass band and a stop band in a part of the pass band, and a reflection echo from a target having at least zero moving speed in the stop band. The filter used as the band is used.

As is clear from FIG. 7 and FIG. 8, when the received signal is filtered using a filter that takes into account the velocity range of the target of the present invention, it is from the seabed where the velocity is zero or from the plankton layer having almost no velocity. It is possible to remove the reflected echo and display only the reflected echo from the target moving around at a constant speed. In addition, by simultaneously displaying the results of filtering using a conventional filter that does not consider the speed range of the target, the user can grasp the situation in the sea more accurately by comparing both images, and more It will be possible to contribute to further improvement of fishery efficiency.

The block diagram which shows an example of a structure of the underwater detection apparatus by Embodiment 1 of this invention. The figure which shows the specific structure of the zone | band limitation calculating part of the underwater detection apparatus by Embodiment 1 of this invention. The figure which shows the low-pass filter which has the filter characteristic according to the predetermined target velocity range The figure which shows the band pass filter produced | generated by frequency-shifting the low pass filter shown in FIG. The figure which shows the band pass filter which has the stop band in part of the pass band frequency which is generated with the band control arithmetic section The figure which shows the specific structure of the automatic zone | band control part of the underwater detection apparatus by Embodiment 2 of this invention. The figure which shows the example of a screen display (sea bottom consumption) of the underwater detection apparatus by Embodiment 3 of this invention. The figure which shows the example of a screen display (plankton disappearance) of the underwater detection apparatus by Embodiment 3 of this invention Block diagram showing the configuration of a conventional underwater detection device Block diagram showing a specific configuration of an automatic bandwidth control unit in a conventional underwater detection device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Front end interface 2 Transmit beam forming part 3 Beam forming pre-processing part 4 Reception beam forming part 5 Band-limit calculating part 6 Filter processing part 7 Display processing part 21 Frequency shift part 22 Frequency detecting part 23 Filter coefficient calculating part 31, 201 Frequency Detection unit 32, 202 Doppler shift frequency estimation unit 33 Bandwidth calculation unit 34, 204, 205 Multiplexer 35 Filter coefficient generation unit 36 Filter coefficient memory 37, 207 Variable bandwidth filter 101 Transceiver 102 Transmission unit 103 Transmission / reception switching unit 104 1 Stage fixed band filter 105 Amplifier / mixer 106 Second stage fixed band filter 107 Amplifier 108 A / D converter 109 Beam forming unit 110 Automatic band control unit 111 Control unit 112 Speed / direction sensor 113 Detection unit 203 Bandwidth estimation Part 206 mixer

Claims (12)

In an underwater detection device that transmits ultrasonic waves into the water and receives and displays reflected echoes from the object,
An underwater detection apparatus comprising: a filter processing unit that performs filtering of a received signal using a filter coefficient that takes into consideration a velocity range of a target. In an underwater detection device that transmits ultrasonic waves into the water and receives and displays reflected echoes from the object,
An underwater detection device comprising: a filter processing unit that performs filtering of a received signal using a bandpass filter having a stopband in a part of a passband frequency. In an underwater detection device that transmits ultrasonic waves into the water and receives and displays reflected echoes from the object,
A band limit calculation unit that generates a desired filter coefficient by frequency-shifting a filter coefficient corresponding to a predetermined target speed range according to the moving speed of the moving object;
An underwater detection device comprising: a filter processing unit that performs filtering of a received signal using a filter coefficient generated by the band limitation calculation unit. In an underwater detection device that transmits ultrasonic waves into the water and receives and displays reflected echoes from the object,
Band limiting to generate independent filter coefficients for each direction from one filter coefficient by frequency-shifting the filter coefficient corresponding to a predetermined target speed range for each direction based on the moving speed and moving direction of the moving object An arithmetic unit;
An underwater detection device comprising: a filter processing unit that performs filtering of a received signal using the filter coefficient generated by the band limitation calculation unit. In an underwater detection device that transmits ultrasonic waves into the water and receives and displays reflected echoes from the object,
A filter coefficient corresponding to a predetermined target velocity range is frequency-shifted for each direction based on the average frequency for each direction obtained by the complex autocorrelation method, so that an independent filter coefficient for each direction is obtained from one filter coefficient. A bandwidth limit calculation unit to be generated;
An underwater detection device comprising: a filter processing unit that performs filtering of a received signal using a filter coefficient generated by the band limitation calculation unit. In the underwater detection apparatus in any one of Claim 3 to 5,
The underwater detection device, wherein the filter coefficient generated by the band limitation calculation unit is a bandpass filter having a stop band in a part of a pass band frequency. The underwater detection device according to claim 2 or 6,
The underwater detection device, wherein the stop band is a band including a frequency of a signal reflected by a target whose moving speed is zero. In the underwater detection apparatus in any one of Claim 2, 6, 7,
The underwater detection device according to claim 1, wherein a stop band of the band-pass filter can be varied with a desired bandwidth. The underwater detection device according to any one of claims 3 to 6,
The band limit calculation unit updates the filter coefficient in real time even during the reception interval in accordance with a change in speed of the moving body, a change in the course, or a fluctuation, and the filter processing unit changes the changed filter coefficient. An underwater detection device characterized by performing filtering processing based on the above. The underwater detection device according to any one of claims 1 to 9,
The filter processing unit filters the same received signal using a filter coefficient having a predetermined bandwidth and a filter coefficient generated by the band limit calculation unit, respectively.
An underwater detection device that simultaneously displays on a display screen filtering results using different filter coefficients. The underwater detection device according to any one of claims 1 to 10,
An underwater detection device further comprising a motion correction function capable of correcting motion of a moving body and transmitting and receiving ultrasonic waves in water. The underwater detection device according to any one of claims 1 to 11,
An underwater detection device that displays a Doppler shift amount of a received signal as color-specific data in accordance with the frequency.