JP2668152B2 - Underwater detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an underwater detection device such as a scanning sonar that transmits and receives ultrasonic waves in a wide range direction.

<Conventional technology> In an underwater detection device that transmits and receives ultrasonic waves in a wide range direction, for example, a full-circle type scanning sonar, an ultrasonic vibrator mechanically or electrically performs a rotary scan to arrive from all directions. To receive an ultrasonic echo. In this case, it is not possible to sufficiently detect the three-dimensional distribution of the school of fish only with the two-dimensional information along the horizontal plane. Therefore, in the related art, information in the depth direction can be obtained by changing the tilt angle for transmitting and receiving ultrasonic waves.

On the other hand, in the prior art, by individually and continuously switching the ultrasonic transducers arranged in an annular shape, virtually one ultrasonic transducer is continuously rotated at a constant speed,
An ultrasonic echo is received by this virtual ultrasonic transducer.
At the time of this reception, as shown in FIG. 1, a received signal (linear FM signal) whose frequency shifts due to the Doppler effect is obtained (FIG. 1 (a)). A pulse filter is compressed (FIG. (C)) by passing through a matched filter (FIG. (B)) having an impulse response of a frequency modulation degree, thereby forming one received beam with enhanced directional characteristics. (For example, see Japanese Patent Publication No. 63-7350).

<Problems to be Solved by the Invention> Meanwhile, a conventional matched filter is of an analog type. For example, a multi-tap delay circuit for delaying a received signal, a resistance element for weighting each output of the delay circuit, and It is configured by combining with a differential amplifier that adds and combines the outputs of the resistance elements. Therefore, conventionally, no consideration has been given to the effect of pulse compression in the matched filter when the tilt angle changes, and the mask pattern that determines the impulse response of the matched filter remains fixed even when the tilt angle changes. there were. That is, in the related art, a mask pattern of an impulse response when the tilt angle is 0 degrees is set, and convolution operation is performed based on the mask pattern.

For this reason, when the tilt angle when transmitting and receiving ultrasonic waves is large, problems such as a decrease in reception sensitivity, insufficient pulse compression to obtain sufficient directional characteristics, and significant occurrence of side lobes are caused. I was

<Means for Solving the Problems> The present invention has been made in view of such circumstances, and solves the above-described conventional problems by enabling pulse compression adapted to a change in tilt angle. Things.

In the present invention, while simultaneously emitting ultrasonic waves in all circumferential directions, receiving ultrasonic echoes coming from a wide range of directions by rotating and scanning the ultrasonic transducer at different tilt angles, and by the Doppler effect In an underwater detection device including an ultrasonic receiver that outputs a reception signal whose frequency shifts and a matched filter that pulse-compresses the reception signal output from the ultrasonic receiver, the ultrasonic receiver is Tilt angle control means for controlling to receive an ultrasonic echo arriving from a predetermined tilt angle direction, and frequency-time characteristic setting means for setting a frequency-time characteristic of the matched filter corresponding to the tilt angle, .

A tilt angle setting means for setting a tilt angle;
Tilt angle control means for controlling the wave receiving means to receive an ultrasonic echo arriving from the tilt angle direction set by the tilt angle setting means, and frequency-time of the matched filter corresponding to the tilt angle Frequency-time characteristic setting means for setting characteristics.

Further, in each of the above inventions, the frequency-
The time characteristic setting means includes: a memory in which each of the frequency-time characteristic patterns of the matched filter corresponding to each of the plurality of tilt angles is stored; and one memory read out from the memory corresponding to the one tilt angle. A latch circuit for latching data of a frequency-time characteristic pattern, wherein the matched filter stores, for each bit, a shift register for storing the received signal and data of the frequency-time characteristic pattern latched by the latch circuit. Each of the multipliers individually multiplies and an adder for adding the output of each multiplier is provided.

<Operation> According to the above configuration, the pulse compression of the received signal is performed by the impulse response that cancels out the influence of the frequency shift based on the tilt angle in the received signal corresponding to each of the different tilt angles. That is, when performing pulse compression for eliminating the influence of the Doppler effect at the time of reception, the influence of the tilt angle at that time is also eliminated.

<Example> A principle for realizing the present invention will be described.

As shown in FIG. 2, while one ultrasonic transducer T rotates on the circumference of the horizontal plane U at a constant angular velocity ωs (peripheral velocity V), transmission and reception of ultrasonic waves at a predetermined tilt angle α are performed. Shall be performed. At this time, a received signal obtained by receiving an ultrasonic echo (center frequency f ₀ ) arriving from the target by the ultrasonic transducer T has a frequency f due to the Doppler effect.
Is a time-shifted linear FM signal.

Here, the horizontal plane U on which the ultrasonic transducer T rotates on the circumference
Then, an orthogonal coordinate system of the x-axis and the y-axis located on the horizontal plane U is set with the circumferential center O as an intersection, and the y-axis is made to coincide with the horizontal vector component of the arrival direction of the ultrasonic echo. If the vector component in the y-axis direction of the peripheral speed V is Vy and the vector component in the direction of the tilt angle α is Vα, the frequency f of the received signal due to the Doppler effect is given by the following equation.

f = f ₀ − (Vα / c) · f ₀ (1) where c is the speed of sound.

On the other hand, the vector component Vα has a scalar amount connecting the intersection position P when the perpendicular line is dropped from the point B of the virtual cuboid to the straight line AE and the current position A of the ultrasonic transducer T,
And the straight line connecting the points P and D is a straight line.
Orthogonal to. Therefore, Vα = Vy · cosα (2) Therefore, from the equations (1) and (2), f = f ₀ − (Vy · cos α / c) · f ₀ (3).

If the angle between the y-axis and the current position of the ultrasonic transducer T is θt, then θt = ωs · t V = r · ωs, so the vector component Vy is Vy = V · sinθt = R · ωs · sin (ωs · t) ≒ r · ωs (ωs · t) = rωs ² t (4) where r is the radius from the center O of the circumference, which is the intersection, to the circumference. . Then, if the amount of frequency shift is Δf, then from equations (3) and (4), Δf = f−f ₀ = −rωs ² tf ₀ cosα / c (5), so that the phase is ∫2πΔfdt = −πrωs ² t ² f ₀ cos α / c + ψ (6) where ψ is a constant.

Thus, the received signal S obtained by the ultrasonic vibrator to rotate (t) is, S (t) = A · cos {2πf 0 t-πrωs 2 t 2 f 0 cosα / c + ψ} (7) Here, A is This is an amplitude term determined by the directional characteristics of the ultrasonic transducer.

From the equation (7), it is understood that the frequency modulation degree of the received signal S (t) changes depending on the tilt angle α.

Since the tilt angle α is set separately and is known in advance, when the received signal is pulse-compressed by the convolution operation in the matched filter, the impulse response characteristic of the matched filter is changed according to the tilt angle α. Then, an appropriate receiving beam can be formed. That is, the impulse response of the matched filter is
A signal obtained by inverting the received signal S (t) based on the above equation (7) on the time axis may be used, and a mask pattern for determining the impulse response of the matched filter while corresponding to a preset tilt angle is stored in advance in a memory. May be stored in the memory.

FIG. 3 is a block diagram of the underwater detection device according to the embodiment of the present invention. In the figure, reference numeral 1 denotes the entire underwater detection device, and 2 denotes an ultrasonic transducer, for example, a number of ultrasonic transducers arranged in a ring and individual ultrasonic transducers. And a switching circuit (both not shown) for continuously switching the ultrasonic waves according to a predetermined tilt angle. A shifted received signal is output.

Reference numeral 4 denotes an A / D converter for digitizing a reception signal from the ultrasonic transducer 2, and reference numeral 6 denotes a matched filter for pulse-compressing the digitized reception signal. In this example, the matched filter 6 includes a serial-input / parallel-output type latch-equipped shift register 8 for storing digitized reception signal data having a predetermined time width, and each data output from the shift register 8 in parallel. Each of the multipliers 10a to 10n individually multiplies the data of the mask pattern latched by the latch circuit 20 described later with each bit, and an adder 12 for adding the outputs of the multipliers 10a to 10n. ing.

Numeral 14 denotes tilt angle setting means for setting a tilt angle for transmitting and receiving ultrasonic waves, and 16 denotes frequency modulation degree changing means for selecting a mask pattern for determining an impulse response of the matched filter 6 corresponding to the set tilt angle. The frequency modulation degree varying means 16 inverts the mask pattern corresponding to each tilt angle to be set, that is, the time axis of the received signal S (t) based on the above equation (7) with the impulse response of the matched filter. And a latch circuit 20 for latching data of one mask pattern read from the memory 18.

Next, the operation of the underwater detection device having the above-described configuration when the received signal is pulse-compressed according to the tilt angle will be described.

In the underwater detector 1, when the tilt angle α is set by the tilt angle setting means 14, the impulse response of the matched filter obtained by inverting the received signal S (t) based on the equation (7) with respect to the time axis corresponds to the tilt angle. The mask pattern to be read is read from the memory 18, and the data of the mask pattern is latched by the latch circuit 20.

On the other hand, by switching the ultrasonic transducers constituting the ultrasonic transducer 2 individually and continuously by the switching circuit, one ultrasonic transducer is virtually continuously rotated at a constant speed. At this time, the transmission and reception of the ultrasonic wave are performed at a predetermined tilt angle α. Therefore, when receiving the ultrasonic echo, the frequency is increased by the above-mentioned (3) due to the Doppler effect.
A received signal (linear FM signal) shifted according to the equation is obtained. Then, after the received signal is digitized by the A / D converter 4, it is sent to the matched filter 6, and the data of the received signal having a predetermined time width is stored in the shift register 8.
Then, the data of the received signal is read out in parallel from the shift register 8 for each bit and supplied to each of the multipliers 10a to 10n.

Each of the multipliers 10a to 10n individually multiplies the output data from the shift register 8 and the data of the mask pattern latched by the latch circuit 20 for each bit. Then, the outputs of the multipliers 10a to 10n are added by the adder 12. As a result, a convolution operation taking into account the tilt angle α is performed, and pulse compression is performed. Moreover, since the processing is digital processing, a result with higher accuracy can be obtained as compared with the case of the analog filter.

In the above embodiment, the memory is set according to the tilt angle.
Although one adaptive mask pattern is read out from 18, a plurality of conventional analog matched filters are provided in parallel, and a mask pattern corresponding to the tilt angle is individually set for each matched filter. It is also possible to switch and use each matched filter according to the angle setting.

<Effects of the Invention> According to the present invention, it is possible to perform pulse compression adapted to a change in tilt angle. As a result, good reception sensitivity can be maintained even when the tilt angle increases,
In addition, excellent effects such as sufficient directional characteristics can be obtained and generation of side lobes can be suppressed.

[Brief description of the drawings]

FIG. 1 is an explanatory view of the operation of pulse compression by a matched filter, FIG. 2 is an explanatory view of the principle of the present invention, and FIG. 3 is a block diagram of an underwater detecting device according to an embodiment of the present invention. 1 ... underwater detection device, 2 ... ultrasonic transducer, 6 ... matched filter, 8 ... shift register, 10a to 10n ...
Multiplier, 12 Adder, 16 Frequency modulation degree varying means,
18 …… Memory, 20 …… Latch circuit.

Claims (3)

(57) [Claims] An ultrasonic wave is simultaneously emitted in all directions, and at the same time, an ultrasonic wave oscillating at a different tilt angle is scanned to receive an ultrasonic echo arriving from a wide range of directions. An underwater detection device comprising: an ultrasonic receiver that outputs a reception signal whose frequency is shifted by; and a matched filter that pulse-compresses the reception signal output from the ultrasonic receiver. A tilt angle control means for controlling to receive an ultrasonic echo arriving from a predetermined tilt angle direction, and a frequency-time characteristic setting means for setting a frequency-time characteristic of the matched filter corresponding to the tilt angle. An underwater detection device, comprising: 2. The apparatus according to claim 2, wherein ultrasonic waves are simultaneously emitted in all directions, and ultrasonic waves arriving from a wide range of directions are received by rotating and scanning an ultrasonic vibrator at different tilt angles, and the Doppler effect is obtained. In an underwater detection device including an ultrasonic receiver that outputs a reception signal whose frequency shifts according to a matched filter that pulse-compresses a reception signal output from the ultrasonic receiver, a tilt for setting a tilt angle Angle setting means, tilt angle control means for controlling the ultrasonic wave receiver to receive an ultrasonic echo coming from the tilt angle direction set by the tilt angle setting means, and corresponding to the tilt angle Frequency-time characteristic setting means for setting the frequency-time characteristic of the matched filter. Apparatus. 3. The frequency-time characteristic setting means includes: a memory storing frequency-time characteristic patterns of the matched filter corresponding to each of the plurality of tilt angles; and a memory corresponding to the one tilt angle. A latch circuit for latching data of one frequency-time characteristic pattern read from the memory, wherein the matched filter includes a shift register for storing the received signal and a frequency-time characteristic pattern latched by the latch circuit. The multiplier according to claim 1 or 2, further comprising: a multiplier for multiplying the data of each of the bits individually for each bit; and an adder for adding an output of each of the multipliers. Underwater detector.