JPH0426714B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an underwater detection device that instantly detects a wide range of underwater directions, and in particular detects reflected waves that return from unnecessary directions among reflected waves that return from a wide range of directions. It relates to removing and detecting only reflected waves returning from a desired direction.

(Prior art) The applicant previously proposed an underwater detection device using pulse compression technology in Japanese Patent Application No. 118004 (1983).
No. 007350).

(Problems to be Solved by the Invention) This invention uses the above-mentioned device provided by the applicant to detect only the reflected waves returning from a desired direction among the reflected waves returning from a wide range of directions in the water, and to prevent unwanted directions from being detected. It is an object of the present invention to further improve the ability to remove returning reflected waves compared to the conventional device described above.

(Means for solving the problem) As a means for solving the problem, an amplifier with a square root characteristic and an amplifier with a square root characteristic are provided. The received wave signal is guided to a matched filter that performs pulse compression, and the output of the matched filter is amplified by an amplifier with a square characteristic.

As is clear from its characteristics, the square-law characteristic amplifier has a small amplification degree for small signals and a large amplification degree for large signals. On the other hand, the pulse compression output of the matched filter differs depending on the return direction of the return signal, and the return signal output from an unnecessary direction is smaller than the return signal from a desired direction. Therefore, by amplifying the output of the matched filter with a square-law characteristic amplifier, the level difference between the return signal from the desired direction and the return signal from the unnecessary direction becomes large, and the return signal from the desired direction is increased. Detection becomes easier. However, since the output of a square-law characteristic amplifier is not linear with respect to the input, distortion occurs in the output signal. A square root amplifier compensates for this distortion. After amplifying the input signal to the matched filter with a square root amplifier, the output of the matched filter is guided to a square root amplifier. Distortion can be compensated for.

(Example) In FIG. 1, a transducer 1, a pulse compressor 2, a display 3, and a controller 4 are an underwater detection device (Japanese Patent Application No. 118004/1986) previously provided by the applicant. 63-007350). That is, after transmitting ultrasonic pulses in a wide range of directions, the transducer 1 receives reflected waves returning from each direction. The reflected waves are received by, for example, an ultrasonic transducer that electronically or mechanically performs uniform circular motion.
Therefore, the transducer 1 outputs the return signals from each direction as time series while undergoing frequency shift. This time-series signal is pulse-compressed in a pulse compressor 2 that functions as a matched filter, and as a result, a directional reception beam is formed. The pulse compressor 2 includes an analog delay circuit 21 and an adder 22, and the time-series signal output from the transducer 1 is sequentially delayed by the analog delay circuit 21. The analog delay circuit 21 takes out delayed outputs at fixed time intervals and guides them to the adder 22. The adder 22 weights each delayed output and sends out the added output. As a result, a directional receiving beam is formed at the output of the adder 22, and a receiving signal from this directional receiving beam is guided to the display 3 and displayed. The display 3 undergoes pixel scanning by the controller 4, and displays the received beam signal output from the pulse compressor 2 in the corresponding direction and position on the display screen. The controller 4 controls the pixel scanning of the display 3 and at the same time controls the uniform circular motion of the ultrasonic transducer in the transducer 1. The directional direction of the received beam outputted from the pulse compressor 2 corresponds to the movement position of the ultrasonic transducer that performs uniform circular motion. Therefore, the controller 4 displays the received signal in the corresponding direction and position on the display screen by scanning the pixels of the display 3 in accordance with the moving position of the ultrasonic transducer.

FIG. 2 shows the directivity characteristics of the directional receiving beam output from the pulse compressor 2, in which, like the well-known directional receiving beam, the main pole beam B _M , the sub-pole beam
It consists of B _s1 , B _{s2 ,} etc. Generally, the signal level of the received signal from the sub-pole beams B _s1 and B _s2 is relatively low, and the signal level of the received signal from the main pole beam _BM is extremely high. Therefore, when the received signal output from the pulse compressor 2 is amplified by the squarer 5 whose amplification degree characteristic is a square characteristic as shown in FIG. 3, sub-pole beams B _s1 and B _s2 are generated. The degree of amplification is relatively small for received signals with relatively low signal levels, and only received signals with high signal levels, such as the main pole beam, are emphasized and amplified. As a result, the squarer 5
As shown in FIG. 4, the received beam of the pulse compressor 2 is divided into a main pole beam B _M and a sub pole beam B _s1 ',
The level difference L _MS ′ such as B _s2 ′ is the level difference shown in Figure 2.
L Outputs extremely large compared to _MS .
Therefore, when the output of the squarer 5 is led to the display 3 and displayed, the signal level of the reflected signal coming back from an unnecessary direction is extremely low compared to the reflected signal coming back from the desired direction. Only the signal can be identified and displayed.

In the above, since the squarer 5 has a square amplification characteristic, the output signal exhibits nonlinear characteristics with respect to the input signal, and signal distortion occurs. A square rooter 6 is provided to compensate for this signal distortion.

The square rooter 6 amplifies the received signal output from the transducer 1 using square root characteristics (FIG. 5).

The transducer 1 outputs reflected signals returning from a wide range of directions in a time series format. Therefore, by square rooting the signal level of the time-series signal output from the transducer 1 and then guiding it to the pulse compressor 2, the signal distortion in the squarer 5 can be compensated for.

(Effects of the Invention) As is clear from the above description, according to the present invention, by amplifying the directional received beam output from the pulse compressor 2 with an amplifier having a square characteristic,
The level difference between the received signal by the main pole beam and the received signal by the sub-pole beam is amplified so as to become extremely large. Therefore, the received signal from the desired direction by the main pole beam and the received signal from the unnecessary direction by the sub-pole beam are sufficiently distinguished, and the received signal from the unnecessary direction is removed to receive the received signal from the desired direction. Only the signal can be displayed.

[Brief explanation of drawings]

Fig. 1 shows an embodiment of the present invention, Fig. 2 is a diagram for explaining the characteristics of the directional received beam of the pulse compressor, and Fig. 3 is a diagram showing the amplification characteristics of the squarer. , FIG. 4 is a diagram for explaining the characteristics of the directional received beam output from the square rooter, and FIG. 5 shows the amplification characteristics of the square rooter in the embodiment.

Claims (1)

[Scope of Claims] 1. In an underwater detection device that transmits ultrasonic pulses in a wide range of directions underwater and receives reflected signals returning from each direction in association with the return direction, an ultrasonic receiving element that receives the reflected signals. receiving means for receiving the reflected signal while mechanically or electronically displacing the receiving position of the reflected signal with respect to the reflected signal, and amplifying the output signal of the receiving means; a first amplifier whose amplification characteristic is a square root characteristic; a matched filter that pulse-compresses the output signal of the first amplifier; and a matched filter that amplifies the output signal of the matched filter and has the amplification degree. directional wave reception in an underwater detection device, comprising a second amplifier having a square-law characteristic, and using an output signal of the second amplifier as a reflected signal associated with the return direction. Beam forming device.