JPH0452584A - Active sonar device - Google Patents

Abstract

PURPOSE:To enable reverberation to be suppressed efficiently and target detection capacity to be improved by obtaining a reverberation spectrum for each traveling speed, determining an adaptive type filter for suppressing it, and then controlling the stop band of a variable band-stop filter. CONSTITUTION:A band-stop filter control circuit 10 receives a speed signal 91 from a speed detection circuit 9, receives a transmission waveform code 111 from a transmission circuit 1, calculates a reverberation spectrum and an adaptive-type filter characteristic, and then outputs a control signal 1001 to a variable band-stop filter 11. The circuit stores a transmission-wave spectrum for each waveform of each transmission sound 3 into memory and reads out a corresponding transmission-wave spectrum depending on the code 111. A doppler shift etc. is added to it to obtain a reverberation spectrum R(f) for calculating an adaptive-type filter characteristic E(f) = G - R(f), where G is a filter gain. Then, the band-stop characteristics of the filter 11 are changed so that it may be conformed to the adaptive-type filter characteristic F(f), thus enabling the reverberation of a reception signal 1101 to be suppressed nearly completely.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an active sonar device, and particularly to a technique for suppressing reverberation components caused by underwater scatterers.

(Prior Art) As is well known, an active sonar device is a device that detects a target by processing the reflected waves of acoustic pulses transmitted underwater. In addition, there are non-uniformities in physical structures in the water, which act as scatterers for the transmitted acoustic pulses, causing reverberation and interfering with target detection. Therefore, a band rejection filter has been conventionally provided to suppress the reverberation components contained in the passed signal.

As this type of active sonar device, for example, the one shown in FIG. 4 is known. In Figure 4,
The transmitter 2 receives the transmission signal 101 from the transmission circuit 1 and sends out the transmission sound 3, which is an acoustic pulse, into the water (Fig. 5(a)).
), the transmitted sound 3 reaches the underwater sonar target 4 and the reflected sound 5
to occur. Furthermore, the transmitted sound 3 acts on the underwater scatterer 15 to generate reverberation 6. Therefore, in addition to the reflected sound 5, the reverberation 6 is received by the delivery device 7. The transfer signal 71 electrically converted by the transfer device 7 is subjected to amplification and band limiting processing in the receiving circuit 8, and is passed through the band rejection filter 1 as a received signal 801.
Enter 7.

On the other hand, the speed of the active sonar device itself is detected by the speed sensor 14, which is converted into a speed signal 91 by the speed detection circuit 9 and input to the center frequency control circuit j6.

The center frequency control circuit 16 sets a center frequency according to the speed, and supplies it to the band rejection filter 17 as a control signal 1601.

Here, the received signal 801 is a superimposition of reflected sound 5 and reverberation 6, as shown in FIG. 5(b), for example. The remaining 41!6 spectrums have a center frequency of f. is of a predetermined bandwidth. Center frequency f.

is the same as the transmission spectrum when the device is stationary, but when the device is moving, it is shifted from the center frequency of the transmission spectrum due to Doppler debt. However, if the moving speed of the device is approximately constant, the spectrum of reverberation 6 will have a center frequency f. is substantially constant, and the bandwidth is also a substantially constant value determined by the waveform of the transmitted sound 3.

That is, as shown in FIG. 5(d), the band-stop filter 17 has a stop band W fixedly set corresponding to a constant bandwidth of the reverberation spectrum, and whose center frequency is set according to the control signal 1.
601, it is set variably.

In this way, the output of the band rejection filter 17 is a received signal 1701 in which the reverberation 6 is suppressed and only the reflected sound 5 is present. This is detected by the detection circuit 12, and the detection signal 12
It becomes 01. The gate circuit 13 performs a threshold value judgment on the detection signal 1201 (FIG. 5(f)), and the target detection signal 13
0] is output.

(Problem to be solved by the invention) As mentioned above, in the conventional active sonar device,
Band-stop filters have a fixed bandwidth and their center frequency is adjusted to match the moving speed of the active sonar device, but when the moving speed changes, there is a problem in that reverberation is insufficiently suppressed and false detections occur. .

That is, although reverberations are input to the delivery device from various angles, the amount of Doppler shift differs for each reverberation. When the speed can be considered to be approximately constant, there is little reverberation, but when the speed changes, the Doppler shift for each reverberation also changes, so the band of the reverberation spectrum expands to the lower frequency side, and the center frequency is, for example, as shown in Figure 5 ( Frequency f when the speed is constant as shown in C).

The frequency fo' is lower than that. The band rejection filter is also controlled so that its center frequency is fO'.

However, since the stopband width W of the bandstop filter is fixed and the bandwidth of the reverberation spectrum is wider than the stopband width W (Fig. 5(e)), the reverberation spectrum is as shown in Fig. 5(g). Components near low frequencies remain unsuppressed, resulting in false detection.

In order to prevent this, it is sufficient to widen the blocking bandwidth W in advance, but this is not a preferable measure because the increased chance of target non-detection increases.

The present invention has been made in view of such problems, and an object thereof is to provide an active sonar device that can effectively suppress reverberation and improve target detection ability even when there is a change in moving speed.

(Means for Solving the Problems) In order to achieve the above object, an active sonar device of the present invention has the following configuration.

That is, the active sonar device of the present invention calculates a reverberation spectrum from the spectrum of acoustic pulses transmitted underwater and the moving speed of the active sonar device, and determines the adaptive filter characteristics for suppressing the calculated reverberation spectrum. Blocking filter! II control circuit; a variable band-stop filter that varies the stop band according to the adaptive filter characteristics and suppresses reverberation components included in the received signal;
It is characterized by having the following.

(Function) Next, the function of the active sonar device of the present invention configured as described above will be explained.

In the active sonar device of the present invention, a reverberation spectrum is obtained for each moving speed, adaptive filter characteristics for suppressing the reverberation spectrum are determined, and the stopband of the variable bandstop filter is thereby controlled.

As a result, it is possible to adapt to changes in reverberation caused by changes in the moving speed of the active sonar device and effectively suppress reverberation, thereby improving target detection ability.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an active sonar device according to an embodiment of the invention. This active sonar device uses a band-stop filter control circuit 10 instead of the center frequency control circuit 16 in the conventional device shown in FIG. 4, and a variable band-stop filter 1 instead of the band-stop filter 17 with a fixed stop band.
1 respectively. Hereinafter, parts related to the present invention will be mainly explained.

The band rejection filter control circuit 10 obtains a speed signal 91 from the speed detection circuit 9, and receives a transmission waveform code I1 from the transmission circuit 1.
1 is obtained, the reverberation spectrum and adaptive filter characteristics are calculated as follows, and the control signal 1001 is output to the variable band rejection filter 11.

First, the reverberation spectrum will be explained. In FIG. 3, the transmitted sound 3 from the transmitter 2 is diffused in a spherical shape, causing reverberation to occur in a large number of scatterers (601 to 605) there. Therefore, reverberations are input to the delivery device 7 from various angles θ. The resulting reverberation spectrum has approximately the same bandwidth (center frequency f) as the transmission spectrum when the speed of the device is constant, but when the speed changes, it spreads toward lower frequencies, and the center frequency f becomes fo'. is as described above. This is rewritten in Figures 2(b) and 2(c).

Here, since both the transmitter 2 and the receiver 7 have directivity, the reverberation level is reduced by the loss Δ due to the transmit/receive directivity 701. Since the number of scatterers (601 to 605) is proportional to the area of unit angular width, the reverberation level also differs from angle to angle. The level of reverberation received from the entire circumference in the angle θ direction is expressed by the following equation (1).

RLV(θ)=L(θ)×S.

Note that θ is the reverberation angle, L(θ) is the amount of directivity loss at the angle θ, and Sl is the area of a unit angular width (for example, 1 degree).

Next, a Doppler shift occurs in the reverberation frequency for each angle, and the Doppler shift f'(θ) at the angle θ is calculated using the following formula (2
).

c+v-cosθ f'(θ)=□・f t −””−・−1−−
--------(2) c-v-cosθ Note that C is the speed of sound in water, and ■ is the speed of the device, which is the content of the speed signal 91. Further, ft is a transmission frequency, which is based on the transmission waveform code 111. That is, the band rejection filter control circuit 10 includes a memory, and stores in advance the transmission spectrum for each waveform of each transmission sound 3 (FIG. 2(a)) in the memory, and the transmission waveform code 1.
11, the corresponding transmission spectrum is read out from the memory. The transmission frequency ft was determined in this manner.

The transmitted wave spectrum P(f) read from the memory is subjected to the reverberation level change and Doppler shift for each angle shown in equations (1) and (2), and these are added to form the reverberation spectrum R(f). Therefore, it is expressed by the following equation (3).

Note that P (f−f' (θ)) is a transmission spectrum without Doppler shift, and D is a directivity width of the device.

From equation (3), it can be understood that as the moving speed changes, the band of the reverberation spectrum expands toward lower frequencies.

Next, the adaptive filter characteristic F(f), which is the content of the control signal 1001, is expressed by the following equation (4).

F (f) = G-R (f) Note that G is the gain of the filter.

The variable band-stop filter 11 changes its stop band characteristic to match the adaptive filter characteristic F(t). As a result, if the reverberation spectrum is as shown in Figure 2(b), the stopband characteristic will be as shown in Figure 5(d), and if the reverberation spectrum is as shown in Figure 2(c), the stopband characteristic will be as shown in Figure 5(e). Therefore, the stopband is variably set to adapt to changes in the reverberation spectrum.

In this way, the received signal ll01 becomes one in which the reverberation is almost completely suppressed, and the gate circuit 13 can correctly perform the threshold value judgment, and the target detection can be performed without error (see Fig. 2 (f). ) (g >).

(Effects of the Invention) As explained above, according to the active sonar device of the present invention, a reverberation spectrum is obtained for each moving speed, an adaptive filter characteristic for suppressing the reverberation spectrum is determined, and a variable band-stop filter Since the stopband of the active sonar device is controlled, the reverberation can be effectively suppressed by adapting to changes in reverberation due to changes in the moving speed of the active sonar device, and the target detection ability can be improved.

[Brief explanation of drawings]

Fig. 1 is a configuration block diagram of an active sonar device according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of the operation of the inventive device, Fig. 3 is a diagram of reverberation generation and directivity, and Fig. 4 is a conventional device. FIG. 5 is an explanatory diagram of the operation of the conventional device. 1... Transmission circuit, 2... Transmitter,
3... Transmitted sound, 4... Sonar target, 5... Reflected sound, 6... Reverberation, 7
...Delivery device, 8...Reception circuit, 9.
... Speed detection circuit, 10 ... Band rejection filter control circuit, 11 ... Variable band rejection filter, 12 ... Detection circuit, 13 ... Gate Circuit, 14... Speed sensor.

Claims (1)

[Claims] a band rejection filter control circuit that calculates a reverberation spectrum from the spectrum of acoustic pulses transmitted underwater and the moving speed of the active sonar device, and determines adaptive filter characteristics for suppressing the calculated reverberation spectrum; the adaptive filter; An active sonar device comprising: a variable band-stop filter that suppresses reverberation components included in a received signal by varying a stop band according to characteristics.