JPS58118973A - Reverberation suppressing circuit - Google Patents

Abstract

PURPOSE:To utilize effectively a reverberation suppressing force notched filter, by deciding the forecasting reverberation frequency corresponding to a deviation angle of an underwater navigating body based on a steering angle and speed information, and controlling local oscillation frequency, etc. CONSTITUTION:In accordance with a steering angle and a speed of an underwater navigating body such as a torpedo for executing active homing, etc., a deflextion angle calculator 20 calculates a deflextion angle of the navigating body. In accordance with this deflextion angle, forecasting reverberation frequency is generated from a reverberation frequency forecasting device 21, a local oscillator 24 for suppressing the reverberation of an ultrasonic receiving wave is controlled through a controller 22, and local oscillation frequency which is mixed with the ultrasonic receiving signal by a mixing circuit 25 is controlled. In this way, a signal applied to a notched filter 27 is not shifted from center frequency, the filter 27 is utilized effectively, a signal-to-reverberation ratio is elevated, and good homing is executed. In this regard, by controlling the center frequency of the notched filter in accordance with the forecasting reverberation frequency, the same result is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dereverberation circuit for an active Hohbang device mounted on an underwater vehicle.

Conventionally, in active homing devices, how to improve the signal-to-reverberation ratio (hereinafter referred to as 8RR) has been a problem. As a means for this purpose, the frequency of reverberation reflected from a non-moving reflector in the front direction of the vehicle, such as floating microorganisms, air bubbles, etc. (hereinafter referred to as a fixed reflector), is determined in advance from the speed of the vehicle and the transmission frequency. We have a method of suppressing this by equipping it with a notched fitter.

This method was effective because the frequency of the echo from the moving target was different from the frequency of the reverberation.

However, when the vehicle searches a wide area while turning, the reverberation frequency shifts, reducing its effectiveness. To further explain this drawback using Fig. 1, in (a), l is the vehicle, 2 is the position in the straight-ahead state, 3 is the velocity vector of the vehicle, 4 is the directivity of the transmitted beam, and the arrow 5 is the direction of the sound wave propagating in the front direction, 6 is the fixed reflector floating in the front direction, arrow 5' is the direction of the reverberation reflected from it in the front direction, 7 is the turning direction of the vehicle, and 7' is the position. The position of the vehicle after a certain time T1 has passed from #2, 8 is the direction of the vehicle at position 7', 6' is the fixed reflector in that direction, and 8' is the same direction from the reflector 6'. 9 is the direction of the reflected reverberation, 9 is the target, and 3' is the 8-directional component of the velocity vector.

It is now assumed that the frequency of the notched filter mounted on the vehicle is set to the reverberation frequency from the 5' direction determined by the velocity vector 3 and the fixed reflector 6. Next, considering the reverberation frequency received at position 7' in the rotated state,
Since this reverberation is reflected from the fixed reflector 6' in the direction 8, it can be seen that its frequency depends on the velocity vector 3'.

That is, it can be seen that since the speed is slower than speed 3, the reverberation frequency is lower.

Therefore, the frequency deviates from the center frequency of the notched filter, and the suppression effect decreases. Figure 1 + b) is a diagram of the received wave Oit during a turn, where T on the horizontal axis is time, La on the vertical axis is the received signal level, B is the reverberation, and the person is the signal from the target that was received immediately after sending the wave. Echo, C shows the echo from the target when Tl has passed after the sending. FIG. 1) shows the output in the conventional system when such a signal is received during a turn. The vertical axis E1 is the output voltage, B is the reverberation output, human is the output of the echo 11, and C is the output of the echo 12. In this way, when turning, the reverberation level increases over time and the echo range SRR is received with a delay.
It turns out that it gets worse.

The present invention predicts the frequency of reverberation that changes in a turning vehicle,
The present invention provides a circuit that solves the above drawbacks and improves 8RR by effectively utilizing a notched filter.

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

FIG. 2 is a system diagram of the embodiment. 120 is a deflection angle calculator;
21 is a reverberation frequency predictor, and 22 is a #controller.

23 is a received signal input terminal, 24 is a local excavator, 2
5 is the frequency of the received signal and the frequency f of the local excavator 24
26 is a band p-wave filter that covers the echo frequency of the received signal; 27 is a notched filter whose center frequency is the frequency fc of the difference; 2
8 is its output.

The operation is as follows: First, the deflection angle calculator 20 calculates the turning rate over time from the rudder angle and speed information of the vehicle over time, and then calculates the reference position of the vehicle at each time (previously determined). Calculate the deflection angle with respect to The reverberation frequency predictor 21 calculates the reverberation frequency f1 based on this deflection angle, taking into account the deviation caused by the turning of the vehicle (the level of the frequency spectrum due to the transmitted beam, received signal, beam directivity, etc.). Predict. The controller 22 determines that the relationship between the predicted reverberation frequency f1, the local oscillation frequency /L, and the center frequency /C of the notched filter is fl&-/L.
The oscillation frequency of the local excavator 24 is controlled in accordance with each predicted reverberation frequency In so that = fc.

By doing so, the reverberation at the expected time of the echo can be effectively suppressed by the notched filter 27, and a good SRR can be obtained. FIG. 3 shows the output in this embodiment, where B is reverberation and A and C are echoes.

In the above embodiment, the oscillation frequency of the local excavator 24 is controlled, but the local oscillation frequency fL is kept constant,
It is clear that the center frequency /C of the notched filter may be controlled.

As described above, the present invention can effectively suppress reverberation even when an underwater vehicle turns, so that good SRR can be obtained.

[Brief explanation of drawings]

1a) to 1(c) are diagrams for explaining conventional dereverberation technology, FIG. 2 is a dereverberation circuit diagram according to the present invention, and 3.
The figure is a diagram showing that reverberation is suppressed by the present invention. 20... Deflection angle calculator, 21... Reverberation frequency predictor, 22... Controller, 24...
... Local oscillator, 25 ... Mixing circuit, 26 ... Group/band P wave a% 27 ... Notched filter. (bノ(C) ′ Figure 2 No. 31￥Il

Claims (1)

[Claims] Sending a sound wave signal from an underwater vehicle and receiving a reflected signal,
In the dereverberation circuit that suppresses reverberation by mixing this delivered signal with a local signal of frequency fL from a local oscillator and passing this mixed good signal through a notched filter having a predetermined center frequency fc, Determine the deflection angle of the underwater vehicle from the rudder angle and speed information of the underwater vehicle. A circuit that predicts the reverberation frequency f1k corresponding to this deflection angle, and a circuit that receives this predicted reverberation frequency a/m, fm-fL'', f
A dereverberation circuit comprising: a controller for controlling the oscillation frequency of the local oscillator or the center frequency of the notched filter, such that C is the oscillation frequency of the local oscillator or the center frequency of the notched filter.