JPH0374956B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention transmits ultrasonic pulses in a wide range of directions underwater, and receives reflected waves returning from each direction separately. The present invention relates to an underwater detection device that displays images at corresponding azimuth positions on a display screen. In particular, it relates to suppressing reflected waves from unnecessary directions when receiving reflected waves returning from various directions.

(Conventional technology) When detecting a wide range of directions underwater instantly, ultrasonic pulses are simultaneously transmitted in a wide range of directions, and the reflected waves returning from each direction are received as reception beams with directivity in each direction. A device is used that displays the received beams in each direction in time series at high speed.

A directional reception beam is generally obtained by combining reception signals of a plurality of ultrasonic receivers by controlling the phase relationship of each reception signal. In this case, the problem is that the directional reception beam has maximum reception sensitivity in the desired direction, and at the same time has some reception sensitivity in unnecessary directions. Therefore, when a relatively strong reflected wave returns from an unnecessary direction, there is a drawback that this reflected wave is seen as if it were a reflected wave returning from a desired direction. This drawback is most noticeable when detecting a wide range of directions on the ocean floor.

For example, in Figure 2, the wide range angle θ of the seabed B
When detecting the direction, looking at the receiving beam 3 in the θ ₀ direction, the main beam M has the maximum receiving sensitivity in the θ ₀ direction, and the receiving beam 3 is received in the unnecessary direction θ _i direction, which is different from the main beam M by θ _S. Sub-beams S and S' having wave sensitivity are formed. Furthermore, when transmitting ultrasonic waves in a wide range of angular directions on the seabed B, extremely strong reflected waves return from the direction of the seabed immediately below. Therefore, as a result of this reflected wave being received by the sub-beam S, the receiving signals in each direction are displayed on the display screen while changing the directivity direction of the directional receiving beam sequentially within a wide range θ. And, as shown in Figure 3, the real image of seabed B
At the same time that B ₀ is displayed, a virtual image B ₀ ' is displayed at a position on the line equidistant D ₀ .

This virtual image B ₀ becomes saturated when the wave reflected by the main beam M is amplified by the amplifier, and as a result, the level difference or level ratio between the wave reflected from the seafloor by the main beam M and the wave reflected by the sub-beam S becomes small. This occurs because it becomes impossible to distinguish based on brightness contrast on the display. For example, in Figure 5,
a indicates the received signal by the receiving beam 3, R ₀ indicates the transmitted pulse, R ₁ indicates the received signal of the seabed reflected wave by the main beam M, and R _s indicates the received signal of the seabed reflected wave by the sub beam S. . The level difference E _d between the main beam seabed reflection wave R ₁ and the sub-beam seafloor reflection is determined by the directional characteristics of the receiving beam 3 (Fig. 2), and in general, the level difference E _d is set to be sufficiently large. It has been decided. Therefore, when the received signal shown in FIG. 5a is displayed on a display, the display brightness of the main beam seabed reflected wave R ₁ and the sub-beam seabed reflected wave R _s can be displayed with sufficiently different display brightnesses. That is, by controlling the brightness of the main beam seabed reflected wave R ₁ to the optimum brightness, it is possible to display the sub beam reflected wave while suppressing it.

However, when the peak value of the received signal a exceeds the saturation level E _s of the amplifier, the amplifier output is saturated and an amplified output as shown in FIG. 5a' is formed.

In this amplified output a′, the level difference E′ _d between the main beam seabed reflected wave R′ ₁ and the sub-beam reflected wave R _s is extremely small. Therefore, when displaying this amplified signal a′,
When the brightness difference between the main beam seabed reflected wave R′ ₁ and the sub-beam reflected wave R _s becomes small, and the brightness of the sub-beam seabed reflected wave R _s is suppressed, the brightness of the main beam seabed reflected wave R′ ₁ is also suppressed at the same time. , making identification difficult.

As mentioned above, when the seabed reflected waves are saturated, the gain control of the amplifier is generally performed so that the seabed reflected waves are below the saturation level. However, in the case of the received signal in Figure 5a, the main beam reflected from the ocean floor
Since _R1 has a very short pulse width, the gain control circuit cannot respond sufficiently. Further, the gain control circuit cannot operate for the sub-beam sea-floor reflected wave that occurs before the output of the main beam sea-bottom reflected wave _R1 . Therefore, conventionally, it is extremely difficult to remove the virtual image _B'0 as shown in FIG.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned drawbacks. That is, the received signals of a plurality of ultrasonic receivers are combined to form a directional received beam, and the received In an underwater detection device that detects a wide range of directions by rapidly controlling the pointing direction of a wave beam, it is possible to detect and remove seabed reflected waves even if they are received by the sub-pole of the directional receiving beam. purpose.

(Means and actions for solving the problem) As a means for solving the problem, detect the signal level of the reception signal of any one of the plurality of ultrasonic receivers that form a directional reception beam. A signal level detector and a gain control circuit that controls the degree of amplification of the directional received beam amplifier according to the signal level are used. A gain control circuit is used that controls the degree of amplification of the directional received beam amplifier in accordance with the signal level of any received signal of the ultrasonic receiver. Then, by controlling the gain according to the signal level of the received signal of any of the ultrasonic receivers, the seafloor reflected waves included in the directional received beam are suppressed.

(Example) In Fig. 1, T ₁ to T _o indicate ultrasonic receivers arranged in a straight line. constitutes a wave device. T ₀ denotes an ultrasonic transmitter which, when excited by the transmitter 1, transmits ultrasonic pulses in a wide range of directions for underwater detection. The reflected waves reflected underwater or on the seabed are transmitted to the ultrasonic receiver T ₁ .
After being received by each of T o to T _o , it is guided to the directional beam forming circuit 2 . A directional beam forming circuit 2 synthesizes the received signals of the ultrasonic receivers _T1 to _T0 to form a directional received beam 3 having directivity in one direction.
form. Then, the directional beam forming circuit 2 scans the direction of the directional received beam 3 at high speed within the range of the detection range angle θ. The scanning speed is such that reflected waves on a substantially equidistant line can be output while the pointing direction changes by θ angle.

For such a directional beam forming circuit 2, a receiving beam directional control device provided by the applicant in Japanese Patent Application No. 121439/1988 can be used.

The directional received signal output from the directional beam forming circuit 2 is guided to a variable gain amplifier 4, amplified, and then guided to a display 5. Pixel scanning of the display device 5 is performed by a scanning circuit 6. For example, as shown in FIG. 4, the pixel scanning is performed to form a fan-shaped raster, and the pixel scanning is performed in synchronization with the detection range angle scanning of the receiving beam 3. Therefore, reflected waves returning from the water are displayed at corresponding azimuth positions on the display screen.

On the other hand, the reception signal of any one of the ultrasonic receivers T ₁ to T _o , for example, the reception signal of the n-th ultrasonic receiver T _o, is A/D. The received signal level is guided to a converter 7 and converted into digital data. The received signal level converted to digital data is stored in a read-only memory 8.
be led to. The setting data of the setting device 9 is also guided to the read-only memory 8.
is the digital data of the A/D converter 7 and the setting device 9
The stored data at the storage address determined by the setting data is read out. The setting device 9 is a variable gain amplifier 4
A setting value is set to set the degree of amplification to a desired degree of amplification.

The stored data read from the read-only memory 8 is guided to the variable gain amplifier 4, and its amplification degree is controlled to an amplification degree corresponding to the value of the stored data.

The amplification degree can be controlled by, for example, preparing multiple amplifiers with different amplification degrees and switching the amplification of the received beam signal to one of the amplifiers. A desired degree of widening can be obtained by appropriately combining and widening. Further, the variable gain amplifier 4 can also be configured using an attenuator. That is,
A plurality of attenuators each having a different degree of attenuation may be used, and these attenuators may be switched, or the combination may be appropriately switched so that the degree of attenuation of the received signal becomes a predetermined amount. Therefore, when an attenuator is used, an amplifier that amplifies the received beam signal can have a constant amplification degree.

The amplification degree control of the variable gain amplifier 4 is performed so that the amplification output does not become saturated when the received beam signal output from the directional beam forming circuit 2 is amplified. For example, if the saturation level of the amplification output of the variable gain amplifier 4 is the amplification degree set by the E _s ' setter 9 is Gcont, and the input level of the received beam signal is Vin, then the variable gain amplification degree 4 is set. The output level Vout when amplified by the amplification degree Gcont is given by Vout=Vin×Gcont...(1) Therefore, in order for this output level Vout not to be saturated, the output level Vout must be Vout≦E _s ... The degree of amplification can be controlled so that …(2) is achieved.

Therefore, amplification degree data such that the output level Vout satisfies equation (2) is written to the memory address specified by the input level Vin and the set amplification degree Gcout of the memory address of the read-only memory 8. Just keep it in there.

(Results of the Invention) As explained above, the present invention uses the received signal level of any one of a plurality of ultrasonic receivers that form a directional received beam to determine the degree of amplification or attenuation of the received beam. It is designed to control the degree of

FIG. 5a shows the output signal of the directional beam forming circuit 2, and FIG. 5b shows the received signal of the ultrasonic receiver T _o . In the reception beam signal a, R ₀ is the transmission pulse, R ₁ , R ₂ , R ₃ , R ₄ are the seabed reflected waves received by the main beam of the directional reception beam 3, and R _s is the sub beam. The figure shows the seafloor reflected waves received by the sea.
Seabed reflected waves R ₁ , R ₂ , R ₃ , and R ₄ are generated when the direction of the directional receiving beam matches the arrival direction of the seabed reflected waves. For example, the seabed reflected wave R ₁ indicates a reflected wave from the seabed point P ₀ (FIG. 2) just below, and is generated when the main beam M of the directional reception beam 3 is directed in the direction of the seabed P ₀ just below.

Now, suppose that the directional reception beam 3 manipulates the detection range θ at time △ _t from time t ₁ to t ₂ , then at time t ₁
After △t/2 hours, a seafloor reflected wave R ₁ is generated. Then, for Δt/2 hours from time t ₁ and for Δ2/2 hours from the generation of the seabed reflected wave R ₁ to time t ₂ , a seabed reflected wave R _s is generated by the sub-beam S or S′. Note that _the time t SUB from when the seabed reflected wave R _s by the sub beam S is received is the time t _SUB from when the ultrasonic pulse is transmitted to when the reflected wave from the seabed point P ₀ immediately below is received. You can find out by finding the time until. Therefore, the distance to the seabed point P ₀ immediately below is D ₀ ,
If the propagation speed of the sound wave is C, it can be obtained by calculating t _SUB =2D ₀ /C.

Next, when the directional receiving beam 3 scans the detection range angle θ during time Δt from time t ₂ to t ₃ , the equiphase wavefront of the detection pulse reaches the seabed surface P ₁ , P′ ₁
Reflected waves R ₂ and R′ ₂ from the point are received. The time at which the reflected waves R ₂ and R' ₂ are received changes by △t〓 ₁ hour with respect to the time at which the directional reception beam 3 is directed toward the seabed point P ₀ directly below. This change time △t〓 ₁ is
This corresponds to the time during which the directional reception beam 3 scans the displacement angle Δθ ₁ of the seabed reflected waves P ₁ and P′ ₁ with respect to the seabed point P ₀ immediately below.

Similarly, at time △t from time _t3 to time _t4 , the equiphase wavefront of the detection pulse reaches the seafloor surface _P2 ,
Reflected waves R ₃ and R′ ₃ from P′ ₂ are received.

In this invention, the ultrasonic receivers T ₁ to T _o
Amplification degree control is performed using one of the received signals (FIG. 5b).

Each of the ultrasonic receivers T ₁ to T _o is almost omnidirectional, so as shown in Figure 5b, each of the ultrasonic receivers T 1 to T o
A reflected wave with an extremely strong signal level is received for a predetermined time t _k from the return time t ₁ of the reflected wave from P ₀ . This signal duration t _k is approximately equal to the time it takes for the equiphase wavefront of the detection pulse to travel on the surface of the seabed B to P ₁ , P ₂ , and P ₃ after reaching the sea bottom P ₀ (Figure 2) directly below. . Therefore, by performing the amplification degree control using the signal level of the received signal b, the amplification degree control can be performed at the same time as the unnecessary reflected wave R _s appears.
Thereby, unnecessary reflected waves R _s can be sufficiently suppressed and only effective reflected waves can be displayed.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, FIG. 2 is a diagram for explaining the detection situation, FIG. 3 is a diagram for explaining a conventional detection image, and FIG. 4 is a display raster of the present invention. FIG. 5 shows a waveform diagram for explaining its operation. 1... Transmitter, 2... Directional beam forming circuit,
3... Directional receiving beam, 4... Amplifier, 5...
Display device, 6...scanning circuit, 7...A/D converter,
8... Read-only memory, 9... Setting device.

Claims (1)

[Claims] 1. In an underwater detection device that transmits and receives ultrasonic pulses in a wide range of directions and displays reflected waves returning from each direction at respective corresponding positions, a plurality of ultrasonic receivers having substantially omnidirectional and identical characteristics are provided. an ultrasonic receiver configured by arranging wave transducers, each ultrasonic receiver generating substantially the same output by receiving reflected waves returning from the wide range of directions, and each receiver of the ultrasonic receiver; By appropriately setting the phase relationship of the wave signals and combining them with each other, a directional received beam having directivity in a specific direction is formed, and by changing the phase relationship, the directional direction of the directional received beam can be changed. The received signal is received based on a directional receiving beam forming circuit that sequentially changes the received signal, and a received signal of any arbitrarily determined ultrasonic receiver among the plurality of ultrasonic receivers. a signal level control circuit that controls an amplifier that amplifies the received signal output from the received beam forming circuit so that the received signal is amplified to a predetermined specific amplification degree corresponding to the received level of the received signal; An unnecessary reflected wave suppression device in a wide range underwater detection device, comprising: