JP3269527B2 - Buried object detection sonar system and its detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a buried object detection sonar, and more particularly, to a buried object detection sonar system for obtaining a buried object echo using both high and low frequencies, a frequency characteristic of a sea bottom acoustic reflection, and an incident angle characteristic. The present invention relates to a buried bar object detection sonar system and a method for detecting the same.

[0002]

2. Description of the Related Art In general, high-frequency sound with high resolution is used for detecting small objects by a sonar. However, since high-frequency sound has a large attenuation rate, a sufficient echo signal cannot be obtained below the sea floor. For this reason, a method of obtaining high resolution using low-frequency sound has been studied for detecting a buried object. For example, in a conventional sonar for detecting a buried object, a system using a low frequency single frequency using a parametric array or the like such as a low frequency transducer array has been proposed. These form a low-frequency, narrow directional beam to allow acoustic signals to reach small objects under the sea floor,
In this method, the presence of an obstacle is recognized from the reflected echo.

[0003] Japanese Patent Application Laid-Open No. 10-153657 discloses a method of detecting a buried object by using both high and low frequencies. It uses a high-frequency / low-frequency side-looking sonar (SLS) method to visualize two different types of received signals and compare them to visually recognize the presence of an object buried on the seabed. It is.

Further, Japanese Patent Laid-Open Publication No. Sho 60-192281 discloses a sludge probe which measures the thickness of a sludge layer by using both high and low frequencies. In this technique, a sub-bottom profiler using a parametric array is configured to measure a round trip time difference between high and low frequencies, and to calculate a thickness of a sludge layer through which low-frequency sound waves pass.

[0005]

However, the one described in Japanese Patent Application Laid-Open No. H10-153657 described above has a problem that the reverberation of the seabed and the echo of the target overlap, and it is difficult to distinguish and separate the two. However, even if a target echo can be received by a low-frequency, high-resolution sonar, it is difficult to know the presence of a buried object.

[0006] Such a problem is that both the target and the sea floor are stationary acoustic reflectors, and there is no characteristic difference such as frequency shift between the two echoes. This is because separation is difficult, and therefore, it is difficult to extract and eliminate a submarine reverberation component from a received signal.

Since undersea reverberation has frequency characteristics, incident angle characteristics, and the like, even if an attempt is made to extract only reverberation components by using a plurality of frequencies, a level difference due to the frequency characteristics remains, and it is difficult to distinguish from a target echo. -There was a problem that separation became difficult.

Further, Japanese Patent Application Laid-Open No. 60-192281 employs a method in which ultrasonic waves having different frequencies are emitted into water, and reflections from the sea bottom and sludge are received and recorded. Therefore, the thickness of the continuous sludge surface can be measured. However, for the same reason as in JP-A-10-153657, there is a problem that a small object buried in the sea floor or the sludge layer cannot be detected. there were.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is directed to a buried object detection sonar capable of detecting a buried object. An object of the present invention is to provide a buried object detection sonar system that obtains a difference signal of a frequency reception signal, corrects the obtained difference signal undersea reverberation characteristic, and improves the S / R ratio, and a method of detecting the same.

[0010]

According to the present invention, there is provided, in accordance with the present invention, a buried object detection sonar system for detecting an object buried under the sea floor, which generates high frequency and low frequency sound. High / low frequency transmitter for transmitting underwater, high frequency receiver for receiving high frequency echoes transmitted from the high / low frequency transmitter and reflected from the sea floor and buried objects, and high / low frequency transmitter for transmission A low-frequency receiving device that receives a low-frequency echo of the sound reflected from the sea floor and the buried object, and a subtractor that takes a difference between the high-frequency echo and the low-frequency echo processed by the high-frequency receiving device and the low-frequency receiving device, An adaptive filter processing unit for canceling the sea bottom echo included in the difference signal input from the subtractor and extracting the echo of the buried object, High-frequency sonar as acoustic frequency /
The low frequency is used together, and the echo of the buried object is extracted from the difference between the two received signals.

The adaptive filter processing section converts the difference signal input from the subtractor from digital to analog.
A / D converter, a single pulse generator that generates a single pulse, an input switch that switches the output of the A / D converter and the single pulse generator, and an adaptation that performs correction processing of a signal input from the input switch. And an FIR filter.
The adaptive FIR filter corrects the influence of the frequency characteristics and the incident angle characteristics of the sea bottom acoustic reflection included in the high / low frequency echo difference signal, and acquires an immersed object echo.

[0012] Also, the sonar system has a high /
A training sequence based on low-frequency acoustic transmission and reception is performed to obtain the frequency characteristics of sea bottom reflection and the incident angle characteristics.

[0013] The adaptive FIR filter of the adaptive filter processing unit is characterized in that an LMS adaptive algorithm is implemented.

Further, the adaptive FIR filter of the adaptive filter processing section is characterized in that an RLS adaptive algorithm is implemented.

Further, a high / low frequency is used as a sonar acoustic frequency for detecting a buried object on the seabed, and a training sequence by high / low frequency acoustic transmission / reception is performed before the search.
It is characterized in that the buried object echo is obtained by correcting the effects of the frequency characteristics and the incident characteristics of the sea bottom acoustic reflection included in the high / low frequency echo difference signal.

Also, a high-frequency transmitting device for generating high-frequency sound and sending it into water, a high-frequency receiving device for receiving high-frequency light transmitted from the high-frequency transmitting device and reflected from the sea floor and buried objects, and a low-frequency sound generating device A low-frequency transmitting device that sends out underwater, a low-frequency receiving device that receives a low frequency of the sound transmitted from the low-frequency transmitting device and reflected from the sea floor and a buried object, a high-frequency receiving device and a low-frequency receiving device. A subtracter that calculates a difference between the processed received signals, and an adaptive filter processing unit that corrects the difference signal input from the subtractor and extracts an echo of the buried object, and a sonar sound for detecting a buried object on the seabed. A high frequency / low frequency is used as the frequency, and an echo of the buried object is extracted from the difference between the two received signals.

Further, a high / low frequency is used as a sonar sound frequency for detecting a buried object on the seabed, and a training sequence by high / low frequency sound transmission / reception is performed before searching.
It is characterized in that the buried object echo is obtained by correcting the effects of the frequency characteristics and the incident characteristics of the sea bottom acoustic reflection included in the high / low frequency echo difference signal.

Further, the present invention is characterized in that an adaptive IIR filter is used in the adaptive filter processing section.

Further, the adaptive IIR filter of the adaptive filter processing section is characterized by implementing an LMS adaptive algorithm.

Further, the adaptive IIR filter of the adaptive filter processing section is characterized in that an RLS adaptive algorithm is implemented.

By adopting the above configuration, high / low
By calculating the difference between the low-frequency signals, the undersea reverberation component included in the low-frequency echo can be reduced, so that the S / R ratio of the received signal can be improved.

Further, since the parametric array is used for high / low frequency transmission, the size of the apparatus can be reduced.

Further, since the frequency characteristics of the undersea reverberation are identified by the training sequence and the correction processing is performed by the adaptive filter, the S / R ratio of the difference signal can be further improved, and as a result, the detection performance can be improved. Can be greatly improved.

[0024]

Next, embodiments of the present invention will be described with reference to the drawings.

According to the present invention, transmission and reception are performed using both high and low frequencies as acoustic frequencies. In low frequency transmission / reception, a received signal in which echoes from the sea floor and a buried object are overlapped, and in high frequency transmission / reception, a received signal of only the sea bottom echo is obtained. By generating a difference signal between the two signals, the sea bottom echo component is reduced and only the buried object echo is extracted. In order to reduce the size of the device, high / low frequency transmission is realized by using a parametric array for high / low frequency transmission by a single transducer. Although a parametric transmitter can be used as a high-frequency receiving system, it cannot be used for a low-frequency receiving system, so a low-frequency receiver is separately prepared.

However, in the difference signals received by these receiving systems, offset components caused by the frequency characteristics of the seafloor reverberation or seafloor scattering intensity and the incident angle characteristics remain. The frequency characteristics and the incident angle characteristics of the reverberation are identified and reproduced during a normal search, and the signal is corrected by further subtracting from the received signal to improve the S / R ratio.

In this embodiment, it is assumed that the present embodiment is mounted and operated on an underwater traveling platform such as a ship or a towing body.

FIG. 1 is a diagram showing the principle of detecting an object buried in the ocean floor (including the ocean floor) 5. As shown in FIG. 1, when detecting a buried object, the buried object 3 is installed on a ship or a towed body, and high-frequency / low-frequency ultrasonic waves 6 are radiated from the high-frequency transmitter 1 to the seabed 5. The high-frequency / low-frequency receiver 2 receives reflected sounds (echoes) 7, 8, and 9 from the receiver.

FIG. 2A is a diagram showing the reception of sea bottom echoes 7 and 9 by the high-frequency receiver 2, and FIG.
It is a figure which shows the reception of the sea bottom and buried object echo 7, 8, 9 by the low frequency receiver 2 '.

The high frequency shown in FIG. 2A has a high resolution and is suitable for detecting details. However, since the waves are short, they are diffused and attenuated halfway, and are not suitable for detecting deep fields. But,
It is less affected by underwater bubbles and underwater noise than at low frequencies. Here, α is the glazing angle, β is the vertical directivity width, h is the seafloor altitude, and R is the range.

On the other hand, the low frequency shown in FIG. 2B is suitable for detecting a buried object in a wide range and continuously, and reaches a target without spreading or attenuating because the wave is long. To detect deep fields.

Due to the characteristics of the high frequency and the low frequency as described above, it tends to seem that it is sufficient to use only the low frequency to detect the object 3 buried in the sea floor 5, but in reality, it is not so. Instead, both signals are used to utilize a parametric effect that occurs when a high-frequency signal and a low-frequency signal, which will be described later, are emitted simultaneously.

FIG. 3A shows a high-frequency echo, and FIG. 3B shows a low-frequency echo.
(C) is a diagram showing the reception levels of these difference signals.

This utilizes the parametric effect of sound waves. The parametric effect is that when high-frequency and low-frequency sound waves are transmitted into the sea, the sound waves interact with each other due to non-linearity in the sea, and the frequency components of the sum and difference of the high and low frequencies are generated. This is an effect that the frequency component shows a very sharp directivity. From FIG. 3, it can be seen from FIG. 3 that the reception level of the high-frequency echo attenuates non-uniformly with time, the low-frequency echo attenuates uniformly, and the difference signal becomes a monotonous mountain-shaped high / low frequency echo. You can see that However, in this state, since the sea bottom echo and the buried object echo are mixed, it is difficult to specify the presence of the buried object.

FIGS. 4 (a) and 4 (b) are diagrams showing reception of a sea bottom echo and a buried object echo by a high frequency receiver and a low frequency receiver, and FIG. FIG. 4D is a diagram showing a high / low frequency echo difference signal before correction in which a difference between frequency signals is obtained, and FIG. 4D shows a submarine echo included in the high / low frequency echo difference signal in FIG. It is a figure which shows the canceled high / low frequency echo difference signal after correction.

The high / low frequency echo difference signal before correction shown in FIG. 4C is a monotonous mountain-shaped high / low frequency echo, whereas the high / low frequency echo difference signal after correction is flat. High / low frequency echo with a pulse in the center.
This pulse indicates the presence of a buried object on the sea floor.

FIG. 5 is a block diagram showing a circuit configuration of the first embodiment of the present invention.

As shown in FIG. 5, a sonar system 10 for detecting a buried object according to the first embodiment of the present invention comprises a high / low frequency transmitting device 11, a high frequency receiving processing unit 12, a low frequency receiving processing unit 13. , An adaptive filter processing unit 14, a high frequency transmitter / receiver 15, a low frequency receiver 16, a CPU 17, and an imaging processing unit 18.

The high / low frequency transmission device 11 is a PWR (Powe
r Amplifier: power amplifier) 11 and adder 112
, A high-frequency oscillator (f1) 113, and a low-frequency oscillator (f1).
2) 114 includes a _{two-frequency} PCW of _f 1, _{f 2} (Pu
lse Continuous Wave) It has a signal generation, addition and amplification function, and generates a parametric array transmission signal from f1 and f2. PCW is a short pulse signal of a single frequency, and is a transmission / reception signal generally used in the field of sonar. This signal has a characteristic that the shorter the transmission pulse width (time), the higher the distance resolution.

The high-frequency reception processing unit 12 includes a transmission / reception switching circuit 122, a PRE (Pre-amplifier) 123 for amplifying a received signal, and a high-frequency BPF (Band Pass Filtration).
ter: high-frequency band-pass filter) 124 and the multiplier 12
5 and LPF (Low Pass Filter)
And a high-frequency detection circuit 127 configured to amplify, band-limit, and base-band demodulate the high-frequency reception signal. Although the received signal is either a frequency f _1, f ₂ available, it is assumed to use f _2.

The low frequency reception processing section 13 includes a reception signal amplification PRE (preamplifier) 132, a low frequency BPF (low frequency band pass filter) 133, a multiplier 134, and an LPF1.
35, and a low-frequency detection circuit 136 configured to amplify, band-limit, and base-band demodulate the low-frequency reception signal.

The high-frequency transmitter / receiver 15 is a transmitter / receiver (transducer) including the frequencies f ₁ and f ₂ in a band.
The transmission signal generated by the low-frequency transmission device 11 is subjected to electric / acoustic conversion and emitted into the sea.

The low-frequency receiver 16 is a low-frequency receiver that is arranged separately from the high-frequency transmitter / receiver 1, receives a low-frequency acoustic signal generated by a parametric array, and performs acoustic / electric conversion. It is for doing.

The parametric array is an array in which every other element is alternately arranged so that the directivities of the elements overlap each other. In FIG. 5, the high-frequency transceiver 15 corresponds to this.

The subtractor 16 generates and outputs a difference signal of the baseband-demodulated high / low frequency reception signal.

The adaptive filter processing unit 14 has an ADC (Anal
og Digital Converter (A / D converter) 144, an adaptive FIR (Finite Impulse Response: finite pulse response) filter 143, a single pulse generator 141, an input changeover switch 144, and a subtractor 145, for subtraction. It digitizes the difference signal generated by the detector 16 from an analog signal to a digital signal, and performs a process of correcting the undersea reverberation characteristic.

The imaging processor 18 performs mapping and drawing of the sea bottom echo by imaging processing performed by a normal side scan sonar or the like.

The CPU 17 is provided with the above components 11, 12, 1
It controls the operations 3 and 18.

Next, a first embodiment of the present invention will be described in detail with reference to FIGS. 4 (a), (b), (c), (d) and FIG.

In FIG. 5, transmission is performed by a high / low frequency transmission device 11 and a high frequency transducer 15. The transmission / reception switching circuit 122 adds two frequency signals having relatively close frequencies,
The signal is amplified and sent to the high frequency transducer 15. As described above, the sum and difference frequencies (secondary waves) are derived from the two-frequency acoustic signals (primary waves) transmitted into water due to the nonlinear effect in water. Of these, the frequency component of the sum with a large propagation attenuation is attenuated in water, and the low-frequency secondary wave, which is the difference component, reaches the sea floor and the buried object 3, is reflected, and is reflected by the high-frequency transducer 15 and the low-frequency receiver. Return to 16. In addition, the primary wave component reaches the sea bottom 5, is reflected, and returns to the high frequency transmitter / receiver 15 and the low frequency receiver 16.

The high-frequency transducer 15 uses a parametric array in which high-frequency transducer elements are arranged in an array in order to give a high-frequency acoustic beam narrow directivity. On the other hand, for a low-frequency acoustic beam, it is not necessary to form a long parametric array because the parametric array forms a low-frequency beam with extremely narrow directivity.

The received high-frequency signal is transmitted to the high-frequency transducer 1
The signal is received at 5, and is subjected to acoustic / electrical conversion. Next, the high-frequency band-pass filter 124
In after being extracted by the high-frequency component f ₂ near band is demodulated into a baseband signal by the high-frequency detector circuit 127. The signal waveform at this point is a high-frequency echo difference signal waveform as shown in FIG.

The reflected low-frequency signal is transmitted to the low-frequency receiver 16.
, Is converted to sound / electricity, amplified by the preamplifier 132 to a level required for demodulation, and extracted by the low-frequency band-pass filter 133 only in the band near the low-frequency components f ₁ -f _2. The signal is demodulated into a baseband signal by a detection circuit 136. For the reference signal, a difference frequency (secondary wave, f ₁ −f ₂ ) is generated by the oscillator 137 and used. The signal waveform at this point is a low-frequency echo difference signal waveform in which the sea bottom reverberation and the target object echo overlap as shown in FIG. 4B, but since the S / R ratio is generally poor, the signal waveform is buried from this waveform. It is extremely difficult to determine a characteristic echo waveform indicating the presence of the object 3.

Next, the difference signal of the high / low frequency reception waveform is generated by the subtractor 16. As shown in FIG. 4 (c), the waveform of the difference signal shows a characteristic echo indicating the presence of the buried object 3 slightly emphasized as compared with FIG. 4 (b). However, since the waveform shown in FIG. 4C still contains an offset component depending on the frequency characteristics and incident angle characteristics of the submarine reverberation, the adaptive FIR filter 143 removes the offset component and improves the S / R ratio. A / D converter 14 reproduces the reverberation characteristics
4 by subtracting from the output signal of FIG. 4 to obtain FIG. At this time, the adaptive FIR filter processing unit 14 turns on the filter input switch 142 to the single pulse generator 141 side.
Then, an impulse is input in a state where the tap coefficients identified as the undersea reverberation characteristics are set in advance, and a correction signal of the undersea reverberation characteristics is output.

The corrected difference signal is digitized from an analog signal to a digital signal by the A / D converter 144 of the adaptive filter processing unit 14 and sent to the image processing unit 18, where the signal is processed in the same manner as a normal side scan sonar. The received signal is converted into a two-dimensional image.

In order to identify the seafloor reverberation characteristics, a training sequence is provided prior to the above operation. In the training sequence, the filter input switch 142 is set to A
The / D converter 144 is turned ON, and transmission / reception is performed with respect to the sea bottom where no buried object 3 exists. When the high / low frequency reception signal is processed and the digitized difference signal is input to the adaptive FIR filter 143, the LMS (Least-Mean-Square)
e: Least-mean-square) Tap coefficients are identified in the input signal by an adaptive algorithm. The system identification accuracy can be confirmed by the final output signal (residual output).

Note that the training sequence is to perform detection on a trial basis before starting the actual detection. By doing so, it is possible to check in advance whether the system operates normally or whether a predetermined result is obtained.

The LMS algorithm estimates a gradient vector from converged data, and does not require measurement and inverse matrix operation for correlation.

In this embodiment, the following specifications are used.

Using a general side scan sonar specification as a model, the glazing angle α in FIG. 1 is 45 °, the vertical directivity width β = 30 °, and the platform is the seafloor altitude h.
= 50 m at a speed of about 10 kt.
The high frequency transducer 1 has a center frequency of 200 kHz.
z, ceramic element array with a bandwidth of 20 kHz (directivity width 1
° or less). The low frequency is set to 10 kHz in consideration of the permeability below the sea bottom 5. Therefore, the high frequency transmission signal (primary wave) of the high / low frequency transmission device 11 has f ₁ = 205 k.
Hz and f ₂ = 195 kHz, and 1
Obtain a narrow directional beam of 0 kHz. In addition, the transmission acoustic level is 210 dB or more (re 0 dB = 1 μPa, @ 1) in consideration of the low secondary acoustic level of a general parametric array.
m).

The high-frequency reception processor 12 includes a preamplifier 1
AGC (Automatic Gai)
n Control) to enable the CPU 17 to control the optimum amplifier gain. Separating extracting the frequency f ₂ echo signal using a center frequency 195 kHz, the ones around the passband width 10kHz in frequency band-pass filter 124.
The high frequency detection circuit 127 includes a multiplier 195 and an LPF 126 for a 195 kHz transmission signal.

The low frequency receiver 16 has a center frequency of 10 k
A secondary wave echo is received using a receiver of Hz. AGC is used for the preamplifier 132 as in the high-frequency reception processing system, but the bias value of the amplifier gain is increased by about 40 dB. This is because the secondary wave component of the parametric array generates only an acoustic level about 40 dB lower than the primary wave. A low-frequency band-pass filter 133 having a center frequency of 10 kHz and a pass bandwidth of about 5 kHz is used. The low-frequency detection circuit 136 is a multiplier 1 for multiplying the output signal of the oscillator 137 having a secondary wave frequency of 10 kHz by
34 and the LPF 135.

The A / D converter 144 operates at a high frequency (200 k
Hz), a sampling rate satisfying a range resolution required for a side scan sonar is 1 MHz, and a bit resolution is about 12 bits.

The adaptive FIR filter 143 has the number of taps necessary to reproduce the reflected signal from the range R,
The MS adaptation algorithm is implemented, and the output signal of the A / D converter 144 is captured in the training sequence to perform system identification. Filter input switch 142 is C
PU17 control, A / D in training sequence
Output of converter 144, single pulse generator 1 during normal search
41 is appropriately switched. At the time of normal search, the single pulse generator 141 outputs a pulse in synchronization with the start of output of the A / D converter 144, and the adaptive FIR filter 143 outputs a correction signal by this input.

Incidentally, instead of the LMS adaptation algorithm, an RLS (Recursive-Least-mean-Square) adaptation algorithm may be used. The RLS adaptation algorithm is L
The convergence speed is much faster than the MS adaptation algorithm.

The operation of the first embodiment of the present invention will now be described with reference to FIGS. 1, 3 and 5.

In FIG. 5, a low-frequency differential frequency (secondary wave) is derived from a two-frequency high-frequency transmission signal (primary wave) transmitted from the high-frequency transducer 15. Both the primary wave and the secondary wave reach the sea bottom 5 and are reflected. However, since the secondary wave has a low frequency, part of the acoustic energy passes through the sea bottom 5 and reaches the buried object 3 and is reflected. And return to the seabed 5. As described above, the echo roughly includes the following three types of components. (1) High frequency sea bottom echo (frequency f ₁ and f ₂ ) (2) Low frequency sea bottom echo (frequency f ₁ -f ₂ ) (3) Low frequency buried object echo (frequency f ₁ -f ₂ ) The acoustic component of the high-frequency sea floor echo (1) is received by the high-frequency transducer 15, converted into an electric signal, and transmitted to the transmission / reception switching circuit 122. The reception signal is transmitted and received by the transmission / reception switching circuit 12.
In step 2, the signal is distributed to the preamplifier 123 and amplified to a level required for demodulation. An appropriate value of the amplifier gain is preset by the CPU 17. Next, after extracting only the high-frequency component f ₂ band by the high-frequency band-pass filter 124, the signal is demodulated into a baseband signal by the high-frequency detection circuit 127. The signal waveform at this point is a reverberation signal as shown in FIG.

The low-frequency echoes (2) and (3) are received by the low-frequency receiver 16 and converted into electric signals.
At 32, the signal is amplified to a level required for demodulation. Although an appropriate value is preset for the amplifier gain by the CPU 17, the preamplifier 12 of the high frequency reception
3 is set higher by about 40 dB. Next, the low-frequency band-pass filter 133 extracts only the band near the low-frequency components f ₁ -f _2, and then demodulates the low-frequency detection circuit 136 into a baseband signal. The reference signal is generated by simulating the difference frequency (secondary wave) by the oscillator 137 and used. The signal waveform at this point is as shown in FIG.

Next, the difference signal of the high / low frequency reception waveform is generated by the subtractor 16. As shown in FIG. 4 (c), the waveform of the difference signal is such that a characteristic echo indicating the presence of the buried object 3 is emphasized as compared with FIG. 4 (b). The difference signal is digitized by the A / D converter 144 and sent to the imaging processing unit 18, where the difference signal is converted into a two-dimensional image by the same processing as in a normal side scan sonar. However, FIG.
Since the waveform of (1) contains an offset component depending on the frequency characteristic and the incident angle characteristic of sea bottom reflection, it is removed and S
In order to improve the / R ratio, the seafloor reflection characteristics are reproduced by the adaptive FIR filter 143 and corrected by subtracting from the output signal of the A / D converter 144 to obtain FIG. At this time, the adaptive FIR filter 143 is connected to the filter input switch 1
42 is turned on to the single pulse generator 141 side, and an impulse is input in a state where a tap coefficient previously identified as the sea bottom reflection characteristic is set, and a reproduction (correction) signal of the sea bottom reflection characteristic is output.

In order to identify the sea bottom reflection characteristic, a training sequence is provided prior to the above operation. In the training sequence, the filter input switch 142 is turned on at the output side of the A / D converter 144, and transmission / reception is performed with respect to the sea bottom 5 where no buried object 3 exists. When the high / low frequency reception signal, the difference signal, and the digitized signal (training signal) are input to the adaptive FIR filter 143, LM
Tap coefficients are identified in the input signal by the S-adaptive algorithm. The system identification accuracy can be confirmed by the final output signal (residual output).

As described above, according to this embodiment, since the difference between the high-frequency signal and the low-frequency signal is obtained, the undersea reverberation component contained in the low-frequency echo can be reduced.
The ratio can be improved.

Further, since the parametric array is used for high / low frequency transmission, the size of the apparatus can be reduced.

Further, since the frequency characteristics of the undersea reverberation are identified by the training sequence and the correction processing is performed by the adaptive filter, the S / R ratio of the difference signal can be further improved, and as a result, the detection performance can be improved. Can be greatly improved.

In the present embodiment, the specific frequencies of the high frequency and the low frequency are not specified, but the low frequency usually means a low frequency of about 50 KHz, and the high frequency means a high frequency of about 200 KHz. Refers to frequency. However, an arbitrary frequency may be selected without being limited to this range. By doing so, it is possible to easily detect the seabed and the position of the buried object in the seabed, and it is possible to detect the buried object with higher accuracy over a wider range.

Next, a second embodiment of the present invention will be described.

FIG. 6 is a block diagram showing a circuit configuration of the second embodiment of the present invention.

In the above-described first embodiment, the adaptive FIR filter 143 is used for the adaptive filter control unit 14. However, in this embodiment, the adaptive IIR (Infinite Impulse
Response; infinite pulse response) filter 143 'is used.

Since the other structure is the same as that of the first embodiment shown in FIG. 5, the same reference numerals as in FIG. 5 are used.

The output of the adaptive FIR filter 143 is determined only by the current input sample value, and the past input sample value does not affect the current input sample value. In contrast, adaptive IIR filter 143 '
Past input sample values affect current input sample values.

As described above, according to the present embodiment, since the difference between the high and low frequency signals is obtained, the undersea reverberation component included in the low frequency echo can be reduced, so that the S / R of the received signal can be reduced.
The ratio can be improved.

Further, since the adaptive IIR filter 143 'is used, it is possible to perform correction in consideration of current and past temporal elements.

Furthermore, since the frequency characteristics of the undersea reverberation are identified by the training sequence and the correction processing is performed by the adaptive filter, the S / R ratio of the difference signal can be further improved, and as a result, the detection performance can be improved. Can be greatly improved.

Next, a third embodiment of the present invention will be described.

FIG. 7 is a block diagram showing a circuit configuration of the third embodiment of the present invention.

In the first embodiment shown in FIG. 5, the transmission system is shared and downsized by using a parametric array for high / low frequency transmission. / Separated into low-frequency transmitting and receiving systems. As shown in FIG. 7, in the present embodiment, the transmitter / receiver arrays 121 and 131, the high-frequency transmitter 11 ′,
A high frequency receiving unit 12 ', a low frequency transmitting unit 19, and a low frequency receiving unit 13 are provided.

Since the other structure is the same as that of the first embodiment shown in FIG. 5, the same reference numerals as those in FIG. 5 are used.

The high-frequency transmitting / receiving system includes a high-frequency transducer 121
Is separated by the transmission / reception switching circuit 122 into a transmission system / reception system. Oscillator of the transmission system frequency f _H 112
And a power amplifier 111, and the CPU 17
The high-frequency PCW signal is transmitted according to the control. The receiving system mainly includes a preamplifier 123 and a high-frequency bandpass filter 124.
And a high-frequency detection circuit 127.

The low-frequency transmission / reception system has a configuration in which the subsequent stage of the low-frequency transducer array 131 is separated into a transmission system / reception system by a transmission / reception switching circuit 132, similarly to the high-frequency transmission / reception system. The transmission system includes an oscillator 172 having a frequency f _L and a power amplifier 171.
And a low-frequency PC according to the control of the CPU 17.
Transmit the W signal. The receiving system mainly consists of a preamplifier 133,
Low-frequency band-pass filter 134 and low-frequency detection circuit 13
7 is comprised.

The detected high / low frequency received signal is subtracted by a subtractor 1
After the difference signal is generated in step 6, the signal is digitized by the A / D converter 144 and imaged by the image processing unit 18. The training sequence for identifying and correcting the sea bottom reflection characteristic is executed by the adaptive FIR filter 143 as in the first embodiment shown in FIG.

In this embodiment, since a parametric array is not used, the low-frequency transmitting / receiving system requires a long array on one or both of the transmitting and receiving sides to obtain narrow directivity (azimuth resolution). . However, the azimuth resolution may be obtained by using the synthetic aperture method as the processing algorithm of the imaging processing unit 18 instead.

In this embodiment, a PC is used as a transmission signal.
Although a W signal is used, an LFM (Linear Fr
The range resolution may be improved by using a modulation signal such as (Equency Modulation). In this case, the oscillator 1 shown in FIG.
A linear modulation signal generating circuit (not shown) is arranged instead of 12 and 172. Further, a transducer having a wide band performance according to the signal band may be used. Note that LF
M is a signal modulated so that the signal frequency changes linearly, and is widely and generally used not only in sonar but also in radar and the like. This signal has a frequency band of PCW
Because it is wider, higher distance resolution can be obtained.

As described above, according to the present embodiment, since the difference between the high and low frequency signals is obtained, the undersea reverberation component included in the low frequency echo can be reduced, so that the S / R of the received signal can be reduced.
The ratio can be improved.

Further, since the frequency characteristics of the reverberation of the seabed are identified by the training sequence and the correction processing is performed by the adaptive filter, the S / R ratio of the difference signal can be further improved, and as a result, the detection performance can be improved. Can be greatly improved.

Finally, a fourth embodiment of the present invention will be described.

FIG. 8 is a block diagram showing a circuit configuration of the fourth embodiment of the present invention.

In the third embodiment described above, the adaptive FIR filter 143 is used for the adaptive filter control unit 14. However, in the present embodiment, the adaptive IIR (Infinite Impulse
Response; infinite pulse response) filter 143 'is used.

Since the other structure is the same as that of the first embodiment shown in FIG. 5, the same reference numerals as those in FIG. 5 are used.

The adaptive IIR filter 143 'used in this embodiment is the same as that used in the second embodiment, and a description thereof will be omitted. See the second embodiment for details.

As described above, according to the present embodiment, the difference between the high and low frequency signals is obtained, whereby the undersea reverberation component included in the low frequency echo can be reduced, so that the S / R ratio of the received signal can be improved. can do.

Also, the adaptive IIR filter 143 '
Is used, it is possible to perform a correction that also takes into account current and past temporal factors.

Furthermore, since the frequency characteristics of the undersea reverberation are identified by the training sequence and the correction processing is performed by the adaptive filter, the S / R ratio of the difference signal can be further improved, and as a result, the detection performance can be improved. Can be greatly improved.

In the first to third embodiments,
Although the buried object detection sonar system mounted and operated on an underwater sailing platform such as a ship or a towed ship has been described as an example, the present invention is not necessarily limited to these systems, and the first to third systems are not limited thereto. May be arbitrarily combined, or may be mounted on an artificial satellite orbiting the earth's orbit to detect from space. The detecting means may use not only a sound wave but also a beam or the like that reaches a target without diffusing or attenuating even if it enters the sea and can recognize its presence. When such a beam is used, any beam width and frequency may be selected in order to improve the resolution in the distance direction and the azimuth direction.

[0103]

As described above, according to the present invention,
The following remarkable effects are obtained.

(1) By adopting a system that uses both high / low frequency transmission and reception, it is possible to reduce the sea bottom reflection component included in the received signal and to improve the S / R ratio of the received signal. The ability to detect small objects. This makes it possible to search for and detect buried mines and other sounds that were difficult in the past.

(2) Only the echo of the target buried object can be clearly extracted by previously identifying the acoustic reflection characteristics of the sea floor by the training sequence and correcting the received signal by the adaptive filter. Therefore, the detection probability of a small object below the sea floor can be improved. As a result, in application to continuous search of a wide sea area, shortening of operation time and improvement of operation efficiency are realized.

(3) Since the parametric array is used for high / low frequency transmission, the size of the device can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a principle of detecting an object buried in the sea floor (including the water bottom).

FIG. 2A is a diagram illustrating reception of a sea bottom echo by a high frequency receiver, and FIG. 2B is a diagram illustrating reception of a sea bottom and a buried object echo by a low frequency receiver.

FIG. 3A is a diagram showing a high-frequency echo,
(B) is a diagram illustrating a low-frequency echo, and (c) is a diagram illustrating a reception level of the differential signal.

FIGS. 4A and 4B are diagrams showing reception of a submarine echo and a buried object echo by a high-frequency receiver and a low-frequency receiver, and FIG. FIG. 9 is a diagram illustrating a high / low frequency echo difference signal before correction obtained by taking a difference;
FIG. 5D is a diagram illustrating a corrected high / low frequency echo difference signal after canceling the sea bottom echo included in the high / low frequency echo difference signal of FIG. 4C.

FIG. 5 is a block diagram showing a circuit configuration of the first embodiment of the present invention.

FIG. 6 is a block diagram illustrating a circuit configuration according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing a circuit configuration according to a third embodiment of the present invention.

FIG. 8 is a block diagram showing a circuit configuration of a fourth embodiment of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 high / low frequency transmitter 2, 2 ′ high / low frequency receiver 3 buried object 4 sea surface 5 sea floor 6 high / low frequency transmission 7 high / low frequency reception 8 buried object echo 9 sea bottom echo 10 buried Object detection sonar system 11 High / low frequency transmission device 11 'High frequency transmission unit 12 High frequency reception processing unit 12' High frequency reception unit 13 Low frequency reception processing unit 13 'Low frequency reception unit 14 Adaptive filter processing unit 17 CPU 16, 145 Subtractor 19 Low frequency transmission unit 111 Power amplifier 112 Adder 113 High frequency oscillator 114 Low frequency oscillator 121 High frequency transducer 122, 142 Switch 123.132 PRE (Pre Amplifier) 124, 133 BPF (Band Pass Filter) 125, 134 Multiplier 126, 135 LPF (Low Pass Filter) 127 High-frequency detection circuit 131 low-frequency wave receiver 136 low-frequency detector circuit 137 reference frequency oscillator 141 pulse generator 142 input selector 143 FIR (Finite Impulse Response: Finite impulse response) filter 143 ', 143''IIR (Infinite Impulse R
esponse; infinite pulse response) filter 144 ADC (Analog Digital Converter: A / D)
146) Image processing unit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-153657 (JP, A) JP-A-3-115882 (JP, A) JP-A-4-335177 (JP, A) JP-A-5-135 52923 (JP, A) JP-A-7-134061 (JP, A) JP-A-5-223923 (JP, A) JP-A-3-195994 (JP, A) JP-A-8-105976 (JP, A) JP-A-10-20045 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01S ⁷ /52-7/64 G01S 15/00-15/96 G01V 1/00

Claims (11)

(57) [Claims] 1. A buried object detection sonar system for detecting an object buried on the seabed, comprising:
A low-frequency transmitting device; a high-frequency receiving device that receives high-frequency echoes transmitted from the high / low-frequency transmitting device and reflected from the sea floor and a buried object; a submarine and a buried object transmitted from the high / low-frequency transmitting device. A low-frequency receiving device that receives a low-frequency echo of the sound reflected from the device; a subtractor that calculates a difference between the high-frequency echo and the low-frequency echo processed by the high-frequency receiving device and the low-frequency receiving device; An adaptive filter processing unit for canceling the sea bottom echo included in the difference signal input from the vessel and extracting an echo of the buried object, comprising: a high frequency / low frequency as a sonar acoustic frequency for detecting a buried object under the sea. The adaptive filter processing unit also converts the difference signal input from the subtractor from digital to analog.
A / D converter for converting the data into a single pulse, a single pulse generator for generating a single pulse, and switching between the outputs of the A / D converter and the single pulse generator
An input changeover switch for correcting a signal input from the input changeover switch;
An adaptive filter, wherein the adaptive filter is included in the high / low frequency echo difference signal.
The effects of the frequency response and incident angle
A buried object detection sonar system that corrects and acquires a buried object echo . 2. The buried object detection sonar system according to claim 1, wherein the adaptive filter is an adaptive FIR filter. 3. The buried object sonar system according to claim 1, wherein a training sequence by high / low frequency sound transmission / reception is performed before searching to obtain a frequency characteristic of sea bottom reflection and an incident angle characteristic. Buried object detection sonar system. 4. The buried object detection sonar system according to claim 2 , wherein the adaptive FIR filter of the adaptive filter processing unit is LM.
A buried object detection sonar system characterized by implementing an S-adaptive algorithm. 5. The buried object detection sonar system according to claim 2 , wherein the adaptive FIR filter of the adaptive filter processing unit is RL.
A buried object detection sonar system characterized by implementing an S-adaptive algorithm. 6. A method for generating high-frequency and low-frequency sound, and
And receiving high-frequency echoes reflected from the sea floor and buried objects.
The low frequency of the sound reflected from the sea floor and buried objects.
Receiving an echo, and calculating a difference between the received high-frequency echo and the low-frequency echo.
Taking, and the seabed included in the difference signal input from the subtractor
Cancel surface echo and extract echo of buried object
Steps to detect objects buried under the sea floor
High sonar sound frequency for detecting buried objects
Buried object from the difference between the two received signals
A method for detecting a buried object by extracting a body echo , wherein a high / low frequency is used as a sonar sound frequency for detecting a buried object on the seabed, and a training sequence by high / low frequency sound transmission / reception is performed before each of the above steps is performed. Teka
A method for detecting the buried object echo by correcting the effects of the frequency characteristics and the incident angle characteristics of the sea bottom acoustic reflection included in the high / low frequency echo difference signal to obtain the buried object echo. 7. A buried object detection sonar system for detecting an object buried on the seabed, comprising: a high-frequency transmitter for generating high-frequency sound and transmitting it into water; A high-frequency receiving device that receives the reflected high-frequency wave; a low-frequency transmitting device that generates low-frequency sound and sends it out to the water; and a low-frequency sound that is sent from the low-frequency transmitting device and reflected from the sea floor and buried objects. A low-frequency receiving device that receives a frequency, a subtractor that takes a difference between the received signals processed by the high-frequency receiving device and the low-frequency receiving device, and a difference signal that is input from the subtractor to correct the buried object. comprising an adaptive filter unit for extracting an echo, and a combination of high-frequency / low frequency as sonar acoustic frequency for detecting submarine buried object, the adaptive filtering Is analog differential signal inputted from the subtractor from the digital
A / D converter for converting the data into a single pulse, a single pulse generator for generating a single pulse, and switching between the outputs of the A / D converter and the single pulse generator
An input switch and an input from the input switch
An adaptive filter that performs a correction process on the signal obtained by the high / low frequency echo difference signal.
The effects of the frequency response and incident angle
A buried object detection sonar system that corrects and acquires a buried object echo . 8. A switch for generating high-frequency sound and transmitting it into water.
The sea floor and buried objects transmitted from the high-frequency transmitter
Receiving the high frequency reflected from the antenna , generating low-frequency sound and transmitting it into the water, and transmitting the low-frequency sound from the low-frequency transmitter to the sea floor and a buried object.
Receiving the low frequency of the sound reflected from the
When, of treatment with the high-frequency receiver and the low-frequency receiver apparatus
Taking the difference between the received signals, and correcting the difference signal inputted from the subtractor to bury the object.
Extracting the echo of the buried seabed
A sonar for detecting buried objects on the seabed to detect objects
Both high frequency and low frequency are used as the acoustic frequency,
Buried object detection for extracting an echo of deaths object embedding the issue of differences
The method comprises using a high / low frequency as a sonar sound frequency for detecting a buried object under the sea, performing a training sequence by high / low frequency sound transmission and reception before performing each of the steps, and then performing a high / low frequency echo. A method for detecting a buried object, comprising: correcting an influence of a frequency characteristic and an incident angle characteristic of a sea bottom acoustic reflection included in a difference signal to obtain the buried object echo. 9. The buried object detection sonar system according to claim 1, wherein an adaptive IIR filter is used in the adaptive filter processing unit. 10. The buried object detection sonar system according to claim 9, wherein the adaptive IIR filter of the adaptive filter processing unit is LM.
A buried object detection sonar system characterized by implementing an S-adaptive algorithm. 11. The sonar system for detecting a buried object according to claim 9, wherein the adaptive IIR filter of the adaptive filter processing unit is RL.
A buried object detection sonar system characterized by implementing an S-adaptive algorithm.