JPH11311672A - Fish finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fish finder or a reverberation detection device that can discriminate the dimension of a target and hence the type of fish, without using conventional double frequency system accompanying various kinds of problems. SOLUTION: A fish finder and a reverberation detection device are provided with transmission parts 1, 2, 3, 4, 5, and 6 for transmitting a tone burst signal, receiving parts 6, 5, 7, and 8 for receiving a reflected wave that appears after transmitting the tone burst signal as a reception signal, a narrow-band filter 9a and a wide-band filter 9b that are composed of a digital filter and an analog filter for filtering the reception signal, and a signal-processing part 10 for processing the output of the wide/narrow-band filters and performing B scope display, while adding different coloring and luminance according to a level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reverberation detecting device such as a fish finder, and more particularly to a fish finder having an improved function of discriminating a fish species.

[0002]

2. Description of the Related Art A fish finder mounted on a fishing boat emits a burst of ultrasonic waves having an appropriate time width in water and receives a reflected wave from a target fish shoal to detect the fish shoal. Is configured. This burst-like ultrasonic wave is obtained by causing an ultrasonic wave of several tens kHz to several hundred kHz to appear over a burst time width of several tens μsec to several msec.
Also called a tone burst signal. For the names and waveforms of such tone burst signals,
Please refer to Figure 2.3 on page 162 of "Marine Acoustic-Fundamentals and Applications-" (edited and published by the Ocean Acoustics Research Group in 1984).

The tone burst signal generates an electric signal by passing a continuous sine wave, which can also be called a carrier wave, through a switch for a burst time width, or operating a sine wave oscillator for a burst time width. The generated electric signal is generated by driving an ultrasonic transducer (also called a transducer, an electric / acoustic transducer or an ultrasonic transducer). Such a burst signal is simply referred to as a pulse signal, and the above-described burst time width is also referred to as a pulse width.

The target length (reflectance: reflected power / incident power) is reduced when the length of the target is smaller than the wavelength of the ultrasonic wave, and the length of the target and the type of fish are determined. . When two types of burst signals having different frequencies are emitted to the same target and the respective reflected waves are received, if the level of the reflected wave of the short wavelength is higher than the level of the reflected wave of the long wavelength, the length of the target is reduced. Can be determined to be between the shorter wavelength and the longer wavelength. Conventionally, the method of determining the length of the target from the level difference between the reflected waves of the two frequencies has been generally adopted.

[0005] For example, an ultrasonic wave having a frequency of 200 kHz and 28 kHz
It is assumed that an ultrasonic wave having a frequency of Hz is emitted to a target having a size of 2 cm to 3 cm. For a 200 kHz ultrasonic wave, its wavelength (0.75 cm) is shorter than the target length, so a large level of reflected wave can be obtained, but for a 28 kHz ultrasonic wave, its wavelength (5.3 cm) is longer than the target length Therefore, the level of the reflected wave decreases. From the relationship between the level of the reflected wave and the wavelength of the radiated ultrasonic wave, the size of the target is 2 to 3 cm, and it is estimated that appropriate fish species are shirasu and shrimp. About this, Japanese Patent Publication No. 40-2555
Please refer to No. 5 Gazette, etc.

[0006]

The above-described conventional two-frequency system has the following disadvantages. If the radiation patterns of two ultrasonic transducers (transducers) that emit ultrasonic waves of different frequencies are different, if a reflected wave cannot be obtained at a certain frequency, the cause is the length and wavelength of the target as described above. , Or because the target is outside the radiation pattern. When the wavelength of the ultrasonic wave is λ, considering that the directivity angle of the radiation pattern of the disk transducer having the diameter D is given by 29.5 λ / D, 1
It is extremely difficult to make the radiation pattern the same for two frequencies that differ by nearly an order of magnitude. For example, frequency 28k
Transducer that emits ultrasonic waves of Hz, frequency 200 k
To achieve the same directional angle as a transducer for Hz, it is necessary to set the diameter to 7 times and the area to 49 times, but it is extremely difficult to match the radiation pattern considering the side lobes and other points. It is.

Since the levels of the reflected waves are compared for two frequencies that differ by almost one digit,
It is necessary to match the sensitivity of each transmitting and receiving system, but this is considerably difficult. It is conceivable to add an individual sensitivity adjustment mechanism to each transmission / reception system, but complicated adjustment work is required.

[0008] The length of the target to be detected is limited. When an ultrasonic wave having a frequency of 30 kHz (wavelength 5 cm) or more is used as the low frequency side, the level of a reflected wave from a target having a size of 3 to 5 cm or more becomes constant, and the dual frequency method cannot be applied.

In the two-frequency system, the level of the reflected wave at each frequency is processed using a difference system or the like. Therefore, even if the level of the reflected wave on the low frequency side is higher than the level of the reflected wave on the high frequency side, The same determination is made as in the reverse case, and erroneous identification is likely to occur.

Accordingly, an object of the present invention is to provide a fish finder capable of discriminating the size of a fish species, generally a target, without using the conventional two-frequency method having the above-mentioned disadvantages. It is in.

[0011]

According to the fish finder of the present invention which solves the above-mentioned problems of the prior art, a transmitting section for transmitting a tone burst signal, and a reflected wave appearing after transmitting the tone burst signal Receiving section, a narrow band filter for filtering the received signal, a wide band filter for filtering the received signal, and a signal processing section for processing the output of the narrow band filter and the wide band filter. And

[0012]

According to a preferred embodiment of the present invention, the first and second signal processing units include a display unit for displaying a processed signal on a B scope.

According to another preferred embodiment of the present invention,
Different coloring or brightness depending on the level is attached to the B scope display on the display unit, and each B scope display is written in the adjacent display area.

According to still another preferred embodiment of the present invention, the time width of the transmitted tone burst signal is set in the range of (tens to hundreds) μsec, and the bandwidth of the narrow-band filter is set. Is set in the range of ± (several tens to several hundreds) Hz, and the bandwidth of the wide band filter is set in the range of ± several kHz.

[0015]

FIG. 1 is a block diagram showing a configuration of a fish finder according to an embodiment of the present invention. This fish finder includes a sine wave generation circuit 1, a pulse generation circuit 2, an analog switch 3,
It includes a power amplifier circuit 4, a transmission / reception switch 5, a transducer 6, an amplification / conversion circuit 7, a sensitivity adjuster 8, a narrow band filter 9a, a wide band filter 9b, a signal processing unit 10, and a color display device 11.

The pulse generation circuit 2 synchronizes with a transmission trigger signal of a fixed period supplied from the signal processing unit 10 to
A pulse signal having a fixed time width of μsec is output and supplied to the analog switch 3. A sine wave electric signal having a constant amplitude and a constant frequency of 50 kHz, which is supplied from the sine wave generation circuit 1 to the analog switch 3
By passing through the analog switch 3 which is opened over a burst time width of 0 μsec, it becomes a burst signal having a time width of 200 μsec and is amplified by the power amplifier circuit 4.
The amplified burst signal is supplied to a transducer 6 via a transmission / reception changeover switch 5, and is radiated into water as a tone burst signal converted into a 50 kHz ultrasonic wave.

The tone burst signal emitted into the water and reflected from a target such as a school of fish is received by the transducer 6 and converted into an electric signal. The received burst signal converted into an electric signal is supplied to an amplification / frequency conversion circuit 7 via a transmission / reception switch 5 which is switched from the transmission side to the reception side immediately after the transmission of the tone / burst signal, and is amplified by about 60 dB. After that, the center frequency is converted to an intermediate frequency of about 500 kHz suitable for the configuration of each subsequent filter. This intermediate frequency signal is supplied to a narrow band filter 9a and a wide band filter 9b via a sensitivity adjuster 8. The filtered signals output from each of the narrow band filter 9a and the wide band filter 9b are supplied to the signal processing unit 10.

The signal processing section 10 comprises a preceding analog processing section and a subsequent digital processing section. In the analog processing section at the preceding stage, the filtered signals output from the narrow band filter 9a and the wide band filter 9b are AF-amplified and detected. The detected signal is converted into a digital signal by A / D conversion in a subsequent digital processing unit, converted into image data for B scope display, and written into an image memory.

According to the principle of underwater acoustics by RJ Eurick (Kyoritsu Shuppansha, first edition, 1977, first edition), the tone and tone reflected by the target and received by the transducer are described.
The burst time width (pulse width) of the burst signal (pulse signal) changes according to the size of the target. If the target is plankton sufficiently smaller than the wavelength of the sine wave (carrier) included in the emitted pulse signal (3 cm at a frequency of 50 kHz in this embodiment), the pulse width of the pulse signal reflected by the target is Does not increase. On the other hand, if the target is larger than the wavelength of the carrier of the emitted pulse signal, the pulse width of the reflected pulse signal increases with the size of the target.

According to page 311 of the above document, the increment of the pulse width of the reflected pulse signal is Δt, the size of the target is L, the incident angle of the emitted pulse signal to the target is θ, and the sound velocity in water is If c is satisfied, the following equation is established. Δt = 2L cos θ / c (1) In equation (1), if L = 30 cm, θ = 0, and c = 1500 m / s, Δt = 400 μsec. In this example, 20
Since a pulse signal with a pulse width of 0 μsec is emitted, the pulse width of the reflected pulse signal is greater than this 200 μsec.
It is extended by 400 μsec to 600 μsec.

In this embodiment, the narrow band filter 9a 6d
The B down bandwidth is set to ± 200 Hz, and the 6 dB down bandwidth of the broadband filter 9b is set to ± 8 kHz.
When a reflected pulse signal with a pulse width of 600 μsec generated by reflection from a target such as a squid with a length of about 30 cm passes through this narrow bandpass filter 9a, a pulse width of 20 μm generated by reflection from a minute target such as plankton.
The level of the output signal is increased by about 8 dB as compared with the case where the reflected pulse signal of 0 μsec passes through the narrow band filter 9a. On the other hand, when a reflected pulse signal with a pulse width of 600 μsec passes through the broadband filter 9b,
There is no difference in the output signal level between the case where the reflected pulse signal of μsec passes through the broadband filter 9b.

As described above, when the pulse width of the reflected pulse signal is in the range of several hundreds of microseconds, the output level of the narrow band filter 9a having a bandwidth of ± 200 Hz varies from the target length of several mm to several tens of cm. As the level changes, a large level of change occurs. On the other hand, the output level of the wideband filter 9b having a bandwidth of ± 8 kHz does not change even if the length of the target changes over a range of several mm to several tens of cm.
As described above, the output of the narrow-band filter 9a indicating a change in level according to the length of the target or the type of fish, and the output of the wide-band filter 9b indicating no change in level according to the type of fish are output from the signal processing unit 10 Is processed into image data of the B scope display and written into the image memory 10.

The image data written in the image memory is read out by the data transfer section, transferred to the color display device 11, and displayed on the B scope. According to the B-scope display, as illustrated in FIG. 1, the vertical axis set downwards indicates the distance from the ultrasonic transducer to the underwater reflector, and the horizontal axis indicates the passage of time. . According to the B-scope display, different colors are given according to the signal levels. For example, coloring is performed such that a higher level increases redness, a lower level increases blueness, and an intermediate level becomes white.

The display screen on the right side of the color display device 11 is a B scope display screen of the detection waveform of the reflected pulse signal that has passed through the wide band filter 9b. According to this display screen, a strong reaction based on a strong reflected wave from a reflector that is viewed as the sea floor is displayed at the bottom, and a reflector that exists over a wide range of depths that is considered to be plankton in the sea above the sea floor. A white spot based on a medium level reflected wave from is shown. Even if squid is mixed in this plankton, if the level of the reflected pulse signal from this squid is about the same as the level of the reflected pulse signal from the plankton, even if there is a large difference in pulse width, And plankton cannot be distinguished separately.

The left display screen, which is described together with the right display screen, is a B scope display screen of a detection waveform of the reflected pulse signal that has passed through the narrow band filter 9a. According to this display screen, a reaction based on a strong reflected wave from a reflector that is also seen as the sea floor is displayed at the bottom, and a large white spot that is seen as squid mixed in plankton is displayed. . Even if the level of the reflected pulse signal from the squid is about the same as that from the surrounding plankton, the pulse width of the reflected wave pulse signal from the squid is larger than that from the plankton. Therefore, the level of the reflected pulse signal from the squid after passing through the narrow band filter is about 8 dB higher than that from plankton. As a result, the plankton reaction disappears from the display screen, and only the squid reaction is displayed.

As described above, the reflected pulse signal from the squid and the reflected pulse signal from the plankton cannot be separated on the B-scope display screen of the reflected pulse signal passed through the wide band filter as long as the respective levels are equal. . On the other hand, even if the levels of the reflected pulse signals from both are equal, on the B-scope display screen of the reflected pulse signal after passing through the narrow band filter, the output signal based on the difference between the respective pulse widths is displayed. Both are clearly separated by the level difference.

The pulse width of the pulse signal output from the pulse generation circuit 2 is adjustable so that an optimum value can be selected according to the size of the fish species to be detected. Fish species to be discriminated include squid with a length of about 30 cm, shrimp with a length of about 10 cm, and shirasu with a length of several cm. The extension width of the pulse width by these targets is at most several tens μsec to several hundred μsec. Therefore, it is preferable to transmit a tone burst signal having a pulse width as narrow as possible in order to accurately identify such a small extension width. However, if the pulse width is made too narrow, problems arise in terms of detection ability and the like. In the inventor's view,
The range of several tens μsec to several hundred μsec is suitable.

FIG. 2 shows how the pass loss of a burst signal in a band-pass filter, which is one of the principles of the present invention, changes depending on the time width of the burst signal and the bandwidth of the filter. It is an evaluation device for performing. A carrier wave of 455 kHz is output from the carrier generator 21, and 100 μsec to 5 ms from the variable width pulse signal generator 22.
A pulse with a variable width in the range of c is output. Carrier generator 2
The 455 kHz carrier generated in step 1
In, the carrier signal is converted into a burst carrier determined by the width of the pulse signal output from the variable width pulse signal generator 22, and supplied to the input terminal of the evaluation crystal filter.

If the wavelength of the carrier used is shorter than the length of the fish to be determined,
As the size of the fish increases, the pulse width of the reflected pulse signal increases, as well as the target strength,
That is, the level of the reflected wave increases. Therefore, there is an advantage that the level of the reflected pulse signal after passing through the narrow band filter increases synergistically, the S / N increases, and the identification accuracy increases.

The output of the evaluation crystal filter 24 is
It is supplied to CH2 of the oscilloscope 25. On the other hand, the input of the evaluation crystal filter 24 is supplied to CH1 of the oscilloscope 25, and the pulse signal output from the variable width pulse signal generator is supplied to the external trigger input terminal (EXT) of the oscilloscope 25.

FIGS. 3 and 4 show waveforms displayed on the oscilloscope 25 by an experiment performed using the evaluation apparatus shown in FIG. Crystal filter 24 for evaluation in FIG.
Is set to 455 kHz, which is equal to the frequency of the carrier wave, and the time width is 5 msec, 500 μsec using the pulse signal generator 22 and the analog switch 23 as shown in order from the uppermost stage A to the lowermost stage C. , And a burst signal of 100 μsec, and when the burst signal is input to the crystal filter 24 for evaluation, the input waveforms A to C
The output waveforms are shown in the upper part of each figure and the lower part.

In FIG. 3, the evaluation crystal filter 24 is used.
Is set to ± 8 kHz and the display screen A,
In all of B and C, the horizontal axis is 1 ms / div, and the vertical axis is 100 mV / div.
Set to div. In all of the display screens A, B, and C, the amplitude of the output waveform is attenuated to half the amplitude of the input waveform, but it can be seen that the amount of attenuation does not depend on the time width of the burst signal.

In FIG. 4, the evaluation crystal filter 24 is used.
Is set to ± 200Hz and the display screen A,
In all of B and C, the horizontal axis is set to 1 ms / div, the vertical axis is set to 1 V / div for the upper input waveform, and 50 mV / div for the lower output waveform. As shown in the display screens A, B and C, when the time width of the burst signal becomes smaller than 5 msec and becomes 500 μsec or 100 μsec, the dependence of the output amplitude on the burst time width becomes remarkable.

When the observation results of the above waveforms are summarized in a graph, a curve as shown in FIG. 5 is obtained. The horizontal axis is the time width of the burst signal, and the vertical axis is the peak value (mV) of the output signal of the filter.
It is. The solid line in the figure indicates the characteristics of a narrow band filter having a bandwidth of ± 200 Hz, and the dotted line indicates the characteristics of a wide band filter having a bandwidth of ± 8 kHz.

FIG. 6 is a block diagram showing a configuration of a fish finder according to another embodiment of the present invention. The fish finder of this embodiment includes a carrier generation circuit 31, a pulse generation circuit 32, an analog switch 33, a power amplification circuit 34, a transmission / reception switch 35, a transducer 36, an amplification circuit 37, a sensitivity adjuster 38, an A / D conversion circuit. 39, a narrow band digital filter 40a, a wide band digital filter 40b, a signal processing unit 41, an image memory 42, a data transfer circuit 43, and the color display device 11.

The carrier generation circuit 31 of the fish finder
1 to the transducer 36 have the same configuration and operation as the fish finder shown in FIG. This fish finder differs from that shown in FIG. 1 in that a digital wide / narrow bandpass filter is used instead of an analog wide / narrowband pass filter. This is due to the fact that the data processing speed has been increased with the recent increase in the performance of digital signal processors, and it is becoming possible to perform filtering at a high speed close to real time. By considering the advantages of

To this end, an A / D conversion circuit 39 is provided immediately after the sensitivity adjuster 38 and the transducer 36
The analog received reflected signal which has been subjected to amplification and sensitivity adjustment after being received by the A / D conversion circuit 39 is immediately converted into a digital signal.

The received reflected signal converted into a digital signal is filtered by a narrow band digital filter 40a and a wide band digital filter 40b in a digital signal processor (DSP), and then transferred to a signal processing unit 41. . The signal processing unit 41 corrects the difference in the amount of transmission delay based on the group delay in each digital filter with respect to the filtered digital reception reflection signals transferred from the wide / narrow band digital filters 40b and 40a. Thereafter, image data for displaying the B scope is created and written to the image memory 42. The image signal written in the image memory 42 is read out by the data transfer unit 43, transferred to the color display device 11, and displayed.

As described above, by adopting a configuration in which the wide / narrow band filtering is performed by the digital filter, the filtering characteristics can be easily changed by changing the program, and the discrimination ability can be improved. Also, as compared with the configuration of FIG. 1 in which each of the filtered signals after passing through the wide / narrow analog filter is A / D converted, the received reflected signal before filtering is A / D converted.
According to the configuration of the embodiment of FIG. 6 for performing D conversion, there is an advantage that the number of A / D conversion circuits can be reduced to one. Furthermore, there is an advantage that the stability of the signal is improved by performing the digital processing of the data consistently from the filtering to the drawing processing.

The present invention has been described above by taking the case of a fish finder as an example. However, the echo detection device of the present invention can also be applied to detection of a target other than a school of fish, such as an obstacle that may be present in the water in front of the ship by being attached to the underwater portion of the bow of a ship.

Further, the configuration in which the pass signal of the narrow band filter and the pass signal of the wide band filter are arranged side by side and described together has been exemplified. However, it is also possible to adopt a display method in which the two are displayed back-to-back by inverting the time axes of both, or both are arranged vertically and displayed together.

Also, as a method of displaying the reflected pulse signal after filtering, a method of performing B-scope display has been exemplified. However, the fish finder of the present invention scans the ultrasonic beam radiated from the transducer over an appropriate angle range of 360 ° or less, and converts the detection waveform of the reflected pulse signal into a region having a corresponding scanning angle centered on the transducer. The present invention can also be applied to a device that displays a PPI.

Further, the configuration for displaying the filtered signal in real time has been exemplified. However, the reverberation detection device of the present invention is operated in a state where it is installed in the sea or the like, and the filtered output of the wide and narrow band filter is detected, converted into a digital signal and stored in a recording medium, and recorded after being pulled out of the sea. Processing such as reading and displaying data stored in the medium can also be performed.

Further, an ultrasonic burst signal is emitted,
The configuration for receiving the reflected wave has been exemplified. However,
Not only ultrasonic waves but also other waves such as radio waves can be used.

[0045]

As described in detail above, the fish finder of the present invention is configured to perform processing such as B-scope display after passing the received reflected pulse signal through the wide and narrow band filters. There is an effect that it is possible to realize a fish finder in which various problems associated with the conventional two-frequency system are solved.

According to the embodiment of the present invention in which wide / narrow band filtering is performed by a digital filter, it is easy to change a filtering characteristic by changing a program, and it is possible to improve discrimination ability. In addition, by performing digital processing of data consistently from filtering to drawing processing, A / D
There are advantages that the number of conversion circuits can be reduced and that signal stability is improved.

[Brief description of the drawings]

FIG. 1 is a functional block diagram illustrating a configuration of a fish finder according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of an experimental apparatus for evaluating a filtering characteristic for a tone burst signal (pulse signal), which is one of the principles of the present invention.

3 is an oscilloscope display screen of a waveform of an input pulse signal and a waveform of an output pulse signal of a wideband filter obtained by an experiment using the apparatus of FIG. 2;

4 is an oscilloscope display screen of a waveform of an input pulse signal and a waveform of an output pulse signal of a narrow band filter obtained by an experiment using the apparatus of FIG. 2;

5 is a characteristic diagram showing the relationship between the width of an input pulse signal and the amplitude of an output pulse signal for a narrow band filter and a wide band filter obtained by an experiment using the apparatus of FIG. 2;

FIG. 6 is a functional block diagram showing a configuration of a fish finder according to another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 sine wave generating circuit 2, 32 pulse generating circuit 3, 33 analog switch 5, 35 transmit / receive switch 6, 36 transducer (transmitter / receiver) 9a narrow band analog filter 9b wide band analog filter 40a narrow band digital filter 40b wide band digital filter 10 Signal processing unit 11 Color display device

Claims (11)

[Claims] A transmitting unit for transmitting a tone burst signal; a receiving unit for receiving a reflected wave appearing after transmitting the tone burst signal as a received signal; a narrow band filter for filtering the received signal; A fish finder comprising: a wideband filter for filtering the received signal; a signal processing unit for processing an output of the narrowband filter and a wideband filter. 2. The fish finder according to claim 1, wherein the signal processing unit includes a display unit that displays the processed received signal on a B scope. 3. The fish finder according to claim 2, wherein the B-scope display by the display unit is given different coloring or brightness depending on a level. 4. The fish finder according to claim 2, wherein each of the B scope displays is displayed in an adjacent display area. 5. The fish finder according to claim 1, wherein a time width of the transmitted tone burst signal is set in a range of (tens to hundreds) μsec. 6. The method according to claim 1, wherein a bandwidth of the narrow band filter is ± (several tens to several hundreds) Hz, and a bandwidth of the wide band filter is ± several kHz. Characterized fish finder. 7. The fish finder according to claim 1, wherein the narrow band filter and the wide band filter are digital filters whose characteristics can be changed by a program. 8. A transmitting unit for transmitting a tone burst signal, a receiving unit for receiving a reflected wave appearing after transmitting the tone burst signal as a received signal, a narrow band filter for filtering the received signal, A fish finder comprising: a wide band filter for filtering the received signal. 9. The fish finder according to claim 8, wherein the narrow band filter and the wide band filter are digital filters whose characteristics can be changed by a program. 10. A transmitting unit for transmitting a burst signal, a receiving unit for receiving a reflected wave appearing after transmitting the burst signal as a received signal, a narrow-band filter for filtering the received signal, A reverberation detection device, comprising: a broadband filter for filtering. 11. The echo detecting apparatus according to claim 10, wherein the narrow-band filter and the wide-band filter are digital filters whose characteristics can be changed by a program.