JPH01262491A - Active sonar equipment - Google Patents

Abstract

PURPOSE:To detect a reflected sound from a target effectively by varying the attenuation quantity and band width of the center frequency of an active sonar equipment band-pass filter with time right after transmission and varying the band width with the width of sent pulses. CONSTITUTION:A sound wave generated by a transmission signal generator 3 is sent into the sea from a power amplifier 2 through a transmitter/receiver 1 and a reflected sound from the target is received by the transmitter/receiver 1. The received signal is amplified by an amplifier 4 which receives a reflection echo. The amplification output is inputted to a variable band-pass filter 5. The band stopping characteristics of this filter 5 are controlled by a filter controller 6, which controls the variable band stopping characteristics of the filter 5 while obtaining information regarding the sent signal from the generator 3. Consequently, the reflected sound from the target which has large reverberation level is detected and the reflected sound of almost the reverberation center frequency from the long-distance target is easily detected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an active sonar device, and particularly to an active sonar device that detects the presence and direction of a target by transmitting acoustic pulses underwater and receiving reflected echoes from the target. Related to sonar devices.

[Conventional technology]

Conventionally, this type of active sonar device transmits sound waves underwater and receives the reflected sound from the target, and the purpose is to detect the presence, direction, characteristics, etc. of the target. The disadvantage was that it was disturbed by the reverberations (reverberant sounds) from the To compensate for this drawback, the receiving circuit of an active sonar device is provided with a band rejection filter for suppressing reverberation.

[Problem to be solved by the invention]

The conventional band-stop filter described above has a drawback in that if there is sound reflected from the target in the stop frequency band, the reflected sound is also blocked, making it impossible to detect the target.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide an active sonar device equipped with a band-stop filter that can detect sound reflected from a target even when there is a sound reflected from a target in the stop-frequency band.

[Means to solve the problem]

The device of the present invention is an active sonar device that detects the direction of a target by transmitting acoustic pulses underwater and receiving reflected echoes from the target. A width generator and a TVG (Time Variation of Ga) that receives reflected echoes.
1n control) an amplifier, a variable band-stop filter that changes the amount of suppression of the received reverberant signal in accordance with the time from transmission, a filter controller, a transducer that converts an electrical signal and an acoustic signal, and a receiver. and a target detector that detects the target from the signal.

〔Example〕

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. The embodiment shown in FIG. 1 includes a transducer 1. Power amplifier 2. Transmission signal generator 3. TVG amplifier4. Variable bandstop filter 5.
It is configured to include a filter controller 6 and a target detector 7.

The active sonar device transmits sound waves into the sea from a power amplifier 2 through a transducer 1, and receives reflected sound from a target object by the transducer 1. The delivery signal is amplified by a TVG amplifier to detect the target.

The delivery signal includes not only the reflected sound from the target object but also interference sound or reverberation from the sea surface and the seabed. These reverberation levels are determined by the transmission level, pulse width, etc. For example, when the transmission envelope is rectangular, the reverberation level and frequency components are determined by the following equations (1) and (2).

Reverberation G: SL-401ogr+10101o cτ
/2)2ψr”---(1) In formula (1), SL:
Transmission level, ": Distance of reflection point, C: Speed of sound, τ: Transmission pulse width, ψ: Equivalent beam width in equation (2) r.: Transmission frequency, τ: Transmission pulse width Equation (1) and (2) ), the reverberation level is proportional to the transmission level, pulse width, and equivalent beam width, and inversely proportional to the distance.In other words, it can be seen that the reverberation level attenuates over time.

Now, noise is generally present in underwater and sonar devices. Band-stop filters are necessary to attenuate reverberation below the noise level. As mentioned above, as the reverberation level decays over time, the ratio of the reverberation level to noise decreases. In this case, it is possible to reduce the attenuation degree of the band-stop filter and narrow the stop band width, thereby preventing unnecessary attenuation of the reflected sound from the target when its frequency is close to the center frequency of the reverberation. be able to. Also, after enough time has passed, the reverberation level will be below the noise level, so a band rejection filter is not necessary.
By using a band-stop filter to temporally reduce the amount of attenuation of the center frequency and narrowing the bandwidth immediately after transmission, it is possible to effectively detect a target from the reverberation. can.

Furthermore, controlling the bandwidth by the transmission pulse width is also effective in suppressing reverberation.

FIG. 2(a) is a characteristic diagram showing an example of a change in reception level immediately after transmission, and FIG. 2(b) is a characteristic diagram showing an example of a change in frequency bandwidth immediately after transmission.

FIG. 3 is a characteristic diagram showing an example of the temporal control characteristics of the variable band-stop filter in the embodiment of FIG. 1, and FIGS. 3(a) to 3(C) correspond to t1 to t3 in FIG. The band-stop characteristic of the variable band-stop filter 5 shown in FIG. 1 becomes gradual as time elapses from transmission, and the band attenuation amount becomes zero at t3. These variable band rejection characteristics are controlled by a filter controller 6,
The filter controller 6 controls the variable band-stop characteristic of the variable band-stop filter while obtaining information regarding the transmission signal from the transmission signal generator 3.

〔Effect of the invention〕

As explained above, the present invention temporally changes the attenuation amount and bandwidth of the center frequency of the band rejection filter in an active sonar device immediately after transmission, and changes the bandwidth depending on the transmission pulse width. It is possible to effectively detect the reflected sound from a target with a high reverberation level, and it is also possible to easily detect the reflected sound from a distant target near the reverberation center frequency.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, in which the second Ti
fl (a > is a characteristic diagram showing an example of a change in reception level immediately after transmission in an active sonar device, 2nd
Figure (b) is a characteristic diagram showing an example of the temporal change in frequency bandwidth immediately after transmission, and Figure 3 is a characteristic diagram showing an example of the temporal control characteristic of the variable band rejection filter in the embodiment of Figure 1. be. DESCRIPTION OF SYMBOLS 1... Transducer/receiver, 2... Power amplifier, 3... Transmission signal generator, 4... TVG amplifier, 5... Variable band stop filter, 6... Filter controller, 7... ...Target detector.

Claims (1)

[Claims] An active sonar device that detects the direction of a target by transmitting acoustic pulses underwater and receiving reflected echoes from the target includes a transmitting signal generator that transmits acoustic pulses underwater, a power amplifier, and a reflector. TVG receiving echo (Ti
me Variation of Gain control
ol) An amplifier, a variable band-stop filter that changes the amount of suppression of the received reverberant signal in accordance with the time from transmission, a filter controller, a transducer that converts an electrical signal and an acoustic signal, and a received signal. An active sonar device comprising: a target detector for detecting a target from a target;