JPH03115882A - Active sonar apparatus - Google Patents

Abstract

PURPOSE:To suppress reverberation suitably for the conditions of use of all active sonar apparatuses by a method wherein a reverberation spectrum generated by transmission is determined on each transmission and a band-rejection filter being suitable for this reverberation spectrum is employed. CONSTITUTION:A frequency analysis circuit 9 latches a transmission timing signal 14 sent from a transmission circuit 1 and a reception signal 15 obtained immediately after transmission and sends out reverberation frequency analysis data 16 to a band- rejection filter control circuit 10. The circuit 10 calculates from the data 16 an adaptable-type filter characteristic a rejection band width and a rejection central frequency for suppressing reverberation and sends out a filter control signal 17 to a variable band-rejection filter 11. In the filter 11, the central frequency is made to be f0' so that it is adapted to the frequency f0' of the center in a reverberation spectrum and, in addition, the filter characteristic is changed to be an adaptable-type filter characteristic having a rejection band width corresponding to the range of the reverberation spectrum. Thereafter, the filter 11 subjects the signal 15 to an appropriate processing for suppression of the reverberation for each frequency and sends out a processed signal 18 to a detection circuit 12. After detection, a reflection sound in the spectrum 25 exceeding a threshold value is detected by a gate circuit 13 and a target is displayed in a display for the like.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an active sonar device, and in particular, improves target detection performance by effectively suppressing reverberation by adapting to the reverberation spectrum for each usage condition. This invention relates to an active sonar device designed to achieve the following.

[Conventional technology]

The purpose of an active sonar device is to detect a target by transmitting sound waves underwater and receiving reflected sound from the target. However, it has the disadvantage of being disturbed by reverberations from underwater scatterers. A blocking filter 41 was provided.

The transmitting circuit 31 sends a transmitting signal to a wave transmitter 32, and the transmitter 32 converts the transmitting signal from the transmitting circuit 31 into a transmitted sound 33 and transmits the sound into the water. When the transmitted sound 33 reaches a target 34, a reflected sound 35 is generated. Furthermore, the transmitted sound 33 causes reverberation 36 to be generated by the scatterer 44 . These transmission sounds 3
3 and reverberation 36 are received by a wave receiver 37, converted into electrical signals, and sent to a receiving circuit 38. Receiving circuit 3
At B, the electrical signal from the wave receiver 37 is amplified and, after band limiting, is sent to the band rejection filter 41 as a received signal 48 .

On the other hand, the speed detection circuit 39 detects the moving speed of the active sonar device using a moving speed detector 45, and sends a moving speed signal 46 corresponding to the moving speed of the active sonar device to the center frequency control circuit 40. The center frequency control circuit 40 then sends a control signal 47 to the band rejection filter 41 based on the moving speed signal 46.

The band rejection filter 41 suppresses the reverberation of the received signal 48 while changing the center frequency with a fixed bandwidth under the control of the control signal 47 and sends the signal to the detection circuit 42 .

The detection circuit 42 detects the signal from the band rejection filter and sends it to the gate circuit 43, and the gate circuit 43 performs dark value determination and outputs a target detection signal. This target detection signal is then displayed on, for example, a cathode ray tube or the like for use. FIG. 4 shows the reverberation spectrum, band rejection filter characteristics, etc. of this active sonar device. Here, Fig. 4 (a
) shows the output waveform of the transmitted sound 33 in amplitude and time, and (b) and (C) show the reverberation spectrum showing the reverberation generated by the transmitted sound 33 in level and frequency.
(d) and (e) are band rejection filter characteristics showing the characteristics of the band rejection filter 41 in terms of frequency and attenuation amount, (f) and (g
) is a state where the spectrum showing the output of the band rejection filter 41 in terms of frequency and level and the dark value judgment of the gate circuit 43 after detection by the detection circuit 42 are being performed.

FIG. 4(b) shows a reverberation spectrum of the active sonar device in a stationary state, in which a spectrum 52 of the reflected sound 35 overlaps a spectrum 50 of the reverberation 36 centered at the maximum spectral frequency f0. (d) is (
b) is the characteristic of the band rejection filter in the state corresponding to
The center frequency of the filter in the fixed band W state is set to the maximum spectral frequency f0 in (b). The reverberation spectrum is suppressed by this band rejection filter, resulting in a spectrum indicated by CA).

Figure 4 (C) shows the reverberation spectrum of the active sonar device in a moving state, with the maximum spectrum frequency f
The spectrum 58 of the reflected sound 35 overlaps the spectrum 56 of the reverberation 36 centered at 01. (e) is
This is the characteristic of a band rejection filter corresponding to the state of (C). In the characteristic of this filter, in the state of fixed band W, (C
) is the frequency f0 in the resting state of the reverberation spectrum at
The frequency f in the moving state from . ', the center frequency of the band-stop filter is moved to suppress reverberation.

The result of this suppression is the spectrum shown in (g).

As explained above, conventional active sonar devices are
Among the operating conditions, reverberation was suppressed by controlling and adapting the center frequency of the band-stop filter to the center of the reverberation spectrum with a fixed bandwidth, taking into account only the moving speed.

[Problem to be solved by the invention]

Conventional active sonar equipment! In this case, reverberation was suppressed using a band-stop filter considering only the moving speed.
In a stationary state, only the reflected sound spectrum 54 is detected as the target, as shown in Fig. 4(f), but in a moving state, as shown in Fig. 4(g), the reverberation spectrum spreads due to movement. Since the reverberation spectrum 60 was not suppressed, the target was erroneously detected in addition to the reflected sound spectrum 62.

In other words, in conventional active sonar devices, the bandwidth of the band-stop filter is fixed, so the spread of the reverberation spectrum caused by the moving speed of the active sonar device cannot be suppressed, resulting in false target detection. . In addition, the waveform, pulse width, directivity width, and
The reverberation spectrum also changes depending on the depth and attitude of the active sonar device, and the spread of the reverberation spectrum cannot be suppressed by a band rejection filter, resulting in incorrect target detection.

Furthermore, in order to prevent erroneous target detection, it is conceivable to widen the fixed bandwidth, but in that case, there is a drawback that the chance of detecting a target is reduced by the widening of the stop band.

SUMMARY OF THE INVENTION An object of the present invention is to provide an active sonar device that eliminates such drawbacks, suppresses reverberations in accordance with the usage conditions of the active sonar device, and can be expected to improve target detection ability.

[Means to solve the problem]

The active sonar device of the present invention includes: a transmitting circuit that transmits sound waves to a target; a receiving circuit that receives reflected sounds and reverberations caused by the sound waves; and a reverberation spectrum calculated from signals of the transmitting circuit and the receiving circuit. It has a frequency analysis circuit, a band-elimination filter control circuit that controls the filter to have filter characteristics adapted to the reverberation spectrum, and a variable band-elimination filter that is controlled by the band-elimination filter control circuit and suppresses the reverberation.

〔Example〕

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

FIG. 1 is a circuit block diagram showing one embodiment of the present invention. This active sonar device includes a transmitting circuit 1, a transmitter 2, a receiver 7, a receiving circuit 8, and a frequency analysis circuit 9.
, a band-elimination filter control circuit 10 , a variable band-elimination filter 11 , a detection circuit 2 , and a gate circuit 13 .

The transmission circuit 1 generates a transmission signal and sends it to the wave transmitter 2, and also sends a transmission timing signal 14 to the frequency analysis circuit 9. The transmitter 2 converts the transmission signal from the transmission circuit 1 into a transmission sound 3 and transmits the sound into the water. When this transmitted sound 3 reaches an underwater target 4, it generates a reflected sound 5. Further, the transmitted sound 3 generates residual g6 by the scatterer 19.

The delivery device 7 receives the reflected sound 5 and the reverberation 6, converts it into an electrical signal, and sends it to the receiving circuit 8. The receiving circuit 8 amplifies and band-limits the electrical signal from the transfer device 7, and sends it as a received signal 15 to the frequency analysis circuit 9 and the variable band rejection filter 11.

The frequency analysis circuit 9 takes in the transmission timing signal 4 from the transmission circuit 1 and the reception signal 15 immediately after transmission based on the transmission timing signal I4, performs reverberation frequency analysis, and controls the reverberation frequency analysis data 16 using a band rejection filter. The signal is sent to circuit 10.

The band rejection filter control circuit B10 calculates adaptive filter characteristics for suppressing reverberation from the reverberation frequency analysis data 16 from the frequency analysis circuit 9, and outputs the filter control signal 1.
7 is sent to the variable band rejection filter 11.

The variable band-stop filter 11 takes in the received signal 15 from the receiving circuit 8 and the filter control signal 17 from the band-stop filter control circuit 10, and converts its own filter frequency characteristics into a stop band that suppresses the reverberation spectrum of the reverberation 6. The input received signal 15 is changed to an adaptive filter characteristic having a width and a rejection center frequency, and appropriate dereverberation processing is performed for each frequency to produce a processed signal 18.
is sent to the detection circuit 12. The detection circuit 12 detects the processed signal 18 from the variable band rejection filter 11 and sends the signal to the gate circuit 13.
It is determined whether the processed signal from 2 exceeds the dark value, and if it exceeds the dark value, a target detection signal is output.

This target detection signal is displayed on, for example, a cathode ray tube.

FIG. 2 is a diagram showing the reverberation spectrum and variable band-stop filter characteristics of this embodiment. Figure 2 (a) shows the output waveform of the transmitted sound 3 in terms of amplitude and time, and (b) and (c
) shows the spectrum of reverberation generated by this transmitted sound 3 in terms of level and frequency, (d) and (e) show the characteristics of the variable band rejection filter 11 in terms of attenuation amount and frequency, and ('
).

(g) shows the output spectrum of the variable band-stop filter.

When the transmitter 2 transmits a transmission wave with an output waveform as shown in FIG. 2(a), this transmission wave causes the output waveform as shown in FIG. 2(b).

A reverberation spectrum shown in (C) is obtained. This (b)
, The reverberation spectrum in (C) is based on the waveform, pulse width, directivity width of the transmitted sound, and the moving speed of the active sonar device,
It changes depending on usage conditions such as depth and posture. (b)
Then, spectrum 2 of residual g6 centered at frequency f0
0 includes spectrum 21 due to reflected sound 5,
In (c), frequency 1. A spectrum 24 of the reflected sound 5 is included in a spectrum 23 of the reverberation 6 centered on I. Furthermore, the reverberation spectrum of CC> is wider than the reverberation spectrum of (b), and the center frequency of the spectrum has moved from fo to f0'.

(d) and (e) show the film characteristics of the variable band rejection filter 11 that suppresses reverberation corresponding to the states of (b) and (c), and in the state of (b), the frequency fo is the center frequency. In the state (C), the filter characteristic is adapted to be changed to a filter characteristic having the center frequency at the frequency f0' and a corresponding rejection bandwidth. From these filter characteristics, (f
), the output spectrum of (g) is obtained. (f)
Then, the spectrum 22 due to the reflected sound 5 is the gate circuit 1.
In (g), even if the reverberation spectrum spreads, the spectrum due to reflected sound is 25.
Only one of them was also detected exceeding the dark value.

Next, the operation of this embodiment will be explained. The transmitting circuit 1 is
A transmission wave 3 having the waveform shown in FIG. When the transmitted sound 3 reaches the target object 4, it becomes a reflected sound 5, and also becomes a reverberation 6 due to the scatterer 19.

The reflected sound 5 and the reverberation 6 are received by a receiver 7, converted into electrical signals, and sent to a receiving circuit 8. The receiving circuit 8 amplifies and band-limits the electrical signal from the receiver 7 and sends it as a received signal 15 to the frequency analysis circuit 9 and the variable band rejection filter 11 .

On the other hand, the frequency analysis circuit 9 takes in the transmission timing signal 14 from the transmission circuit 1 and the reception signal 15 immediately after transmission based on the transmission timing signal I4, and analyzes the frequency of reverberation, for example, as shown in the reverberation spectrum shown in FIG. ) and sends the reverberation frequency analysis data 16 to the band-stop filter control circuit 10. The band-stop filter control circuit 10 calculates an adaptive filter characteristic having a stop band width and a stop center frequency for suppressing reverberation from the reverberation frequency analysis data 16, and sends a filter control signal 17 to the variable band-stop filter 11. . In the variable band-stop filter 11, the center frequency is set to (0/) by adapting it to the center frequency f0' in the reverberation spectrum of FIG. 2(C), and
After changing the adaptive filter characteristics to the adaptive filter characteristics shown in FIG. 2(e), which has a stop band width corresponding to the spread of the reverberation spectrum, the received signal 15 is subjected to appropriate dereverberation processing for each frequency. The signal 18 is sent to the detection circuit 12. After the processed signal 13 from the variable band rejection filter 11 is detected by the detection circuit 12, the dark value is determined by the gate circuit 13, and the spectrum 2 in FIG. 2 (g) where the dark value exceeds
The reflected sound of No. 5 is detected and a target detection signal is extracted and displayed on a display or the like. As explained above, the reverberation component is appropriately suppressed while meeting all the usage conditions of the active sonar device, so that the reflected sound of the target is detected and displayed.

〔Effect of the invention〕

As explained above, the present invention calculates the reverberation spectrum generated by transmission for each transmission, and uses a band rejection filter that adapts to this reverberation spectrum, thereby eliminating reverberation while adapting to the usage conditions of all active sonar devices. It has the effect of suppressing the target and improving target detection ability.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram according to an embodiment of the present invention, FIG. 2 is a diagram showing a reverberation spectrum and variable band-stop filter characteristics according to the embodiment of FIG. 1, and FIG. 3 is a diagram showing a conventional technique. The circuit block diagram, FIG. 4, is a diagram showing a reverberation spectrum and variable band-stop filter characteristics according to a conventional technique. 1... Transmission circuit 2... Transmitter 7... Receiver 8... Receiving circuit 9... Frequency analysis circuit 10... Band Blocking filter control circuit 11...
・Variable band-stop filter 12...Detection circuit 13...Gate circuit Figure 2 Figure 4

Claims (1)

[Claims] (1) a transmitting circuit that transmits sound waves to a target; a receiving circuit that receives reflected sound and reverberation caused by the sound waves; and a frequency analysis circuit that calculates a reverberation spectrum from the signals of the transmitting circuit and the receiving circuit; An active sonar device comprising: a band-elimination filter control circuit that controls a filter to have filter characteristics adapted to the reverberation spectrum; and a variable band-elimination filter that is controlled by the band-elimination filter control circuit and suppresses the reverberation.