JP6757083B2 - Echo sounder and multi-beam echo sounder - Google Patents

Description

The present invention relates to an echo sounder and a multi-beam echo sounder that measure depth using ultrasonic waves propagating in water.

Echo sounding technology in the ocean has been used for a long time. As shown in Fig. 1, an ultrasonic pulse is emitted from an ultrasonic transducer, and the echo that the sound wave reflects from the target (sea floor) is captured and underwater. The depth of the sound wave is measured using the propagation speed of the sound wave (about 1500 m / s). Echo sounding devices using this principle have been commercialized for more than 50 years, and even today, depth sounding of the seafloor is performed using this principle. This technique, called echolocation, has remained unchanged, in other words, undeveloped.

The principle is that if an ultrasonic pulse (for example, 1 ms pulse width) is emitted, the reciprocating distance is 1000 m on a seabed of 500 m, and the underwater speed Vu of the sound wave is 1500 m / s, 1000 / Vu = 1000/1500 = 0.667 seconds. After receiving the echo, the ultrasonic pulse is emitted again, and at the same time, the depth of the seabed at a different location is measured as the ship advances. In this way, an echo sounder is a device that sequentially measures the depth of the seabed as the ship sails and displays it on a liquid crystal screen as a recording paper or an image (see, for example, Patent Document 1).

The echo sounding device so far has taken into consideration the sound velocity of ultrasonic waves in water, and controlled the transmission interval so as not to transmit the next echo before the received echo to perform sounding. As shown in FIG. 2, a sounding device provided with only one beam is called a single-beam sounding device, and a fan-shaped sounding device that has appeared in recent years is called a multi-beam sounding device (see, for example, Patent Document 2). The multi-beam sounder can measure a wide range of depths at a time with relatively high density.

When the depth is D and the transmission interval of the transmission pulse is T, and (2D / 1500) <T, the time difference between the transmission pulse and the received echo corresponds to (2D / 1500) as shown in FIG. 3A. The depth can be measured from this time difference. However, in the case of (2D / 1500) ≥ T, as shown in FIG. 3B, since the received echo arrives after the transmission of the next transmission pulse, it becomes difficult to know which transmission pulse the received echo corresponds to. The wrong depth will be measured based on the time difference FD. Therefore, conventionally, the condition of (2D / 1500) <T was required.

If the transmission cycle cannot be shortened, the horizontal resolution of the bathymetry cannot be reduced. The resolution of measurement in the traveling direction (horizontal direction) of the ship will be described with reference to FIG. The horizontal resolution ΔH (m) when the depth D (m) is measured at the ship speed V (m / s) is expressed by the following equation.
ΔH = VT> 2DV / 1500

For example, if a ship sails at 10 kt (10 x 1.852 km / h) and the transmission cycle is 1 second, sounding data can be obtained only about every 5 m. In order to measure the seabed at a depth of 1,000 m, the transmission cycle T must be set to (1,000 x 2) /1,500 = 1.33 seconds or more, but it cannot be measured, but if the ship sails at 10 kt, it will be 1.33. Since it has advanced 6.7 m after a second, the measurement resolution ΔH is 6.67 m. The multi-beam sounder can measure a wide range of depths at once, but the resolution of the ship's direction of travel is similar to that of a single beam.

With conventional echo sounders, the only way to increase the resolution of measurement is to reduce the speed of the ship. Therefore, the conventional echo sounder has a problem that the time required for sounding becomes long when the resolution of the sounding is increased.

Further, as shown in FIG. 5, when the seabed is measured by sound waves, the depth of measurement due to the sway of waves with respect to the reference sea surface may be deeper or shallower than the true seabed. The seafloor depth obtained by the measurement is as shown in FIG. 6, and the distance to the true seafloor cannot be measured. In order to solve this problem, it is necessary to detect the sway component and correct the sway.

As described above, the conventional echo sounder cannot shorten the transmission cycle, and the transmission cycle is longer than or almost equal to the period of sway caused by the wave. Therefore, the sway caused by the influence of the wave is detected and the sway is detected. It was difficult to correct. From the sampling theorem, it is impossible to detect the sway component unless sampling is performed at a frequency that is at least twice the maximum value of the sway frequency component. Therefore, when correcting the sway, conventionally, as shown in Patent Document 3, it has been usual to detect the rotation angle and the amount of displacement of the three axes and perform the sway correction based on the detection result.

Japanese Unexamined Patent Publication No. 2001-083247 Japanese Unexamined Patent Publication No. 2006-220436 JP-A-2010-025739

An acceleration sensor is used to detect the displacement of the sway. The velocity is obtained by integrating the acceleration once, and the displacement amount is obtained by integrating the velocity. Shake detection using such an acceleration sensor has a problem that an error occurs and it is necessary to correct the error. Further, there is a problem that an acceleration sensor is required, which causes an increase in cost.

Therefore, an object of the present invention is to provide an echo sounder and a multi-beam echo sounder capable of performing sway correction using a received signal without using an acceleration sensor.

The present invention is an echo sounding device installed on a moving body that moves on a swaying water surface and detects an object to be measured in water.
A transmission signal forming unit having a modulation circuit for forming a transmission signal by modulating a carrier wave signal by a pseudo-noise sequence generator及beauty pseudo noise sequence signal to generate a pseudo noise sequence signal,
A transmitter that periodically sends out the transmitted signal as ultrasonic waves toward the measurement target located below the moving body,
A receiver that receives an echo due to the ultrasonic waves transmitted from the transmitter being reflected by the measurement target ,
By performing the correlation process by the pseudo-noise sequence signal echoes, the correlator determine what the corresponding echo transmission signal,
A sway correction unit that suppresses the sway component by performing sway correction on the depth raw data corresponding to the time difference between the transmitted signal and the echo .
It is equipped with a display device that displays a signal that detects the output signal of the correlator whose sway component is suppressed in synchronization with the transmission signal .
The display device displays the transmission line extending in the horizontal direction on the upper side of the screen, displays the detected signal of the correlator output signal in color, and sequentially displays the detected signals corresponding to the adjacent transmission timings. Display them side by side
The period of the transmitted signal is (2D / Vu) or less when the velocity of the sound wave in water is Vu and the depth is D, and the sound is satisfied with the sampling theorem as compared with the period of the shaking component. It is a sounding device.
Further, the present invention is a multi-beam echo sounding device installed on a moving body moving on a swaying water surface and detecting an object to be measured in water.
A transmission signal forming unit having a modulation circuit for forming a transmission signal by modulating a carrier wave signal by a pseudo-noise sequence generator及beauty pseudo noise sequence signal to generate a pseudo noise sequence signal,
A transmitter that periodically sends out the transmitted signal as ultrasonic waves toward the measurement target located below the moving body,
A receiver that receives an echo due to the ultrasonic waves transmitted from the transmitter being reflected by the measurement target ,
A correlator that discriminates the echo corresponding to the transmitted signal by correlating the echo with a pseudo-noise series signal,
A sway correction unit that suppresses the sway component by performing sway correction on the depth raw data corresponding to the time difference between the transmitted signal and the echo .
It is equipped with a display device that displays a signal that detects the output signal of the correlator whose sway component is suppressed in synchronization with the transmission signal .
The display device displays the transmission line extending in the horizontal direction on the upper side of the screen, displays the detected signal of the correlator output signal in color, and sequentially displays the detected signals corresponding to the adjacent transmission timings. Display them side by side
The period of the transmission signal is (2D / Vu) or less when the velocity of the sound wave in water is Vu and the depth is D, and the sampling theorem is satisfied as compared with the period of the swaying component.
It is a multi-beam echo sounding device that sends out a large number of ultrasonic beams in a fan shape by a transmitter.

According to the present invention, since the transmission cycle can be shortened, the resolution in the horizontal direction can be increased, for example, the sway component due to the wave can be accurately detected, and the detected sway component can be used. Agitation correction can be performed. Since the acceleration sensor is not used, the cost increase can be prevented and the influence of the error can be reduced. In addition, when the measurement target is a fish, the shadow of the fish is displayed as undulating due to shaking, and there is a problem that the fish species and the like cannot be correctly recognized. The present invention can be correctly recognized when displaying the measurement target. The effects described here are not necessarily limited, and may be any of the effects described in the present specification.

It is a schematic diagram which shows the principle of echo sounding. It is a schematic diagram for demonstrating single beam sounding and multi-beam sounding. It is a waveform diagram used for the explanation of the conventional echo sounding apparatus. It is a schematic diagram used to explain the horizontal resolution of a conventional echo sounder. It is a schematic diagram for explaining the agitation by a wave. It is a schematic diagram for explaining the influence of agitation by a wave. It is a block diagram which shows the structure of an example of an echo sounding apparatus. It is a block diagram used for explaining a correlator in an echo sounder. It is a waveform diagram used for explaining the output of a correlator. It is a schematic diagram explaining the case of displaying a received signal. It is a waveform figure which shows an example of the modulation method of a transmission signal. It is a waveform diagram used for the explanation of an echo sounder. It is a schematic diagram used for explaining the horizontal resolution of an echo sounder. It is a waveform diagram used for the explanation of an echo sounder. It is a schematic diagram used for explaining the horizontal resolution of an echo sounder. It is a schematic diagram which uses the simulation result of the echo sounder for explanation. It is a schematic diagram which uses the simulation result of the improved echo sounder for explanation. It is a schematic diagram which compares and shows the display image by a conventional echo sounder, and the display image by an improved echo sounder. It is a waveform diagram of an example of a transmission signal of an echo sounder. It is a waveform diagram used for the explanation when two Gold Code signals overlap in an echo sounder. It is a schematic diagram for demonstrating the principle of the aperture synthesis side scan sonar. It is a schematic diagram for demonstrating the directional characteristic of aperture synthesis. It is a schematic diagram for demonstrating the principle of aperture synthesis. It is a schematic diagram which shows an example of a point target. It is a schematic diagram which shows the image of an example of a point target. It is a schematic diagram which shows the image before aperture synthesis and the image after aperture synthesis of an example of a point target. It is a schematic diagram which shows the image before aperture synthesis and the image after aperture synthesis of an example of a point target. It is a schematic diagram which shows the image before aperture synthesis and the image after aperture synthesis of an example of a two-point target. It is a schematic diagram used for the explanation of a multibeam echo sounder. It is a block diagram which shows the structure of a multibeam echo sounder. It is a schematic diagram used to explain the agitation caused by waves. It is a schematic diagram which shows the seabed which corrected the sway. It is a flowchart for demonstrating an example of sway correction in one Embodiment of this invention. It is a schematic diagram for demonstrating an example of sway correction in one Embodiment of this invention. It is a block diagram for demonstrating another example of sway correction in one Embodiment of this invention. It is a block diagram for demonstrating another example of sway correction in one Embodiment of this invention. It is a schematic diagram which shows the data before sway correction and the data after sway correction. It is a block diagram for demonstrating still another example of sway correction in one Embodiment of this invention. It is a schematic diagram for demonstrating another embodiment of this invention. It is a block diagram for demonstrating another embodiment of this invention.

Hereinafter, embodiments of the present invention will be described. It should be noted that the embodiments described below are suitable specific examples of the present invention and are provided with various technically preferable limitations. However, the scope of the present invention is particularly limited to the present invention in the following description. Unless otherwise stated, it is not limited to these embodiments.
The description of the present invention is given in the following order.
<1. Improved echo sounder>
<2. Aperture synthesis>
<3. Multibeam echo sounder ＞
<4. Embodiment>
<5. Other embodiments>
<6. Application example>
<7. Modification example>

<1. Improved echo sounder>
When the sway correction is performed on the wave, the sway component can be detected by stopping the ship at sea and detecting the change in water depth due to the ship moving up and down by the wave. Then, the sway correction can be performed by canceling the sway component detected from the sounding measurement result. As described above, since the detection of the sway component can be performed by echo sounding, the following description first describes an improved echo sounder that enables the depth to be measured with a short transmission cycle, and then the sway. The correction will be described.

FIG. 7 shows the electrical configuration of an improved echo sounder. A transmission trigger generator 1 that generates a transmission trigger pulse of a pulse signal having a fixed period is provided, and the transmission trigger pulse is supplied to the Gold Code generator 2 as a PN sequence generator and the display or recording device 10. The display and / or recording device 10 includes a display device such as a liquid crystal display and / or a recording device such as a semiconductor memory and an arithmetic unit for display or recording.

The gold code generator 2 generates a gold code in synchronization with the transmission trigger pulse. A PN (Pseudo random Noise) sequence such as an M sequence other than the Gold Code may be used. The gold code is supplied to the pulse modulator 3, and the gold code is digitally modulated by, for example, BPSK (Binary Phase Shift Keying). The frequency of the carrier wave is several kHz to several hundred kHz
It is said to be z.

The output signal of the pulse modulator 3 is supplied to the transmission amplifier 4, and the transmission amplifier 4 performs processing such as amplification. The output signal of the transmission amplifier 4 is supplied to the transmitter 5. Ultrasonic waves are transmitted from the transmitter 5 into the water. The echo of the emitted underwater ultrasonic wave is received by the receiver 6. An integrated configuration may be used for the transmitter 5 and the receiver 6.

The received data from the receiver 6 is supplied to the receiving amplifier 7, undergoes processing such as amplification, and then supplied to the correlator 8. The output of the correlator 8 is supplied to the detection circuit 9. The correlator 8 extracts the received echo corresponding to the transmitted pulse. The detection circuit 9 performs an operation for display (for example, A / D conversion). The output of the detection circuit 9 is supplied to the display and / or recording device 10, and the time until the echo is received with respect to the transmission pulse is displayed and / or recorded, respectively.

FIG. 8 shows the correlation detection process. The received echo signal is input in series to the shift register SR in 4064 steps. It is preferable to improve the SN ratio by adding a plurality of received echo signals before and after the shift register SR. Noise can be reduced by the addition processing, low transmission output can be achieved, and the device can be miniaturized and power-saving design can be performed. The shift clock that operates the shift register SR is (20 × 8 = 1,600 kHz = 1.6 MHz). This frequency is an example, and a shift clock having a frequency that is at least twice the carrier frequency (20 kHz) can be used. When the received echo signal is supplied to the shift register SR, it is sampled at a frequency eight times that of the carrier signal.

Arithmetic circuits EXA1 to EX127 are provided in parallel with the shift register SR. Each of the arithmetic circuits EXA1 to EX127 is composed of an exclusive OR circuit and an adder circuit (4064 circuit). 4064 bits of the shift register SR are commonly supplied to each of the exclusive OR circuits of the arithmetic circuits EXA1 to EX127.

On the other hand, a replica of the gold code code G1 (replica is 4064 bits), a replica of the code G2, ..., A replica of the code G127 are supplied to each of the exclusive OR circuits of the arithmetic circuits EXA1 to EX127. .. In the exclusive OR circuit, if the bits of the two inputs have the same value, the output becomes "0", and if the bits of the two inputs have different values, the output becomes "1". The 4064-bit output of each exclusive OR circuit is added. If the number of "1" s is N, the addition outputs a signal having an amplitude of the value of N. By taking the negative logic, the output of a large value is obtained so that the two inputs match. The additional output of the arithmetic circuits EXA1 to EX127 is as shown in FIG. The large amplitude output indicates a received echo signal that matches the Gold Codes of the transmit pulse.

FIG. 10 illustrates a case where the display and / or the recording device 10 performs the display. A transmission trigger pulse is supplied to the display and / or recording device 10, and the timing of the transmission trigger pulse is displayed as a transmission line (0 m) on the upper side of the screen. The detection signal from the detection circuit 9 for the transmission trigger pulse is displayed, for example, in color. Since the transmission trigger pulse is a fast repeating signal of several Hz to several tens of Hz, it is compared with the conventional echo sounding device by displaying the detection signals corresponding to each of the transmission trigger pulses from the correlator 8 in order. Then, the sounding image appears several times to several tens of times faster.

FIG. 11 illustrates an example of pulse modulation. For example, the phase is switched between 0 and π corresponding to the gold code bits "0" and "1" every 4 cycles (4 waves) of a 200 kHz carrier wave. The frequency of the carrier wave is an example, and may be another frequency, and a modulation method such as QPSK other than BPSK may be used. Further, not only phase modulation but also amplitude modulation may be used.

Correlation detection is performed by digital signal processing in the correlator 8. One bit is composed of 4 cycles, and each cycle is digitized with 8 samples. Therefore, when the code of the Gold Code is 127 bits, one received echo signal is (127 × 4 × 8 = 4064 bits).

In the improved acoustic measuring device described above, the transmitted signal and the received echo signal (seafloor echo) can be identified. As shown in FIG. 12, the transmission signal A and the transmission signal B have different Gold Codes. It is possible to identify that the received echo signal corresponding to the transmission signal A is received after the transmission signal B and the received echo signal corresponds to the transmission A. Therefore, the conventional limitation on the transmission cycle T ((2D / 1500) <T) can be eliminated.

In the improved acoustic measuring device, the horizontal resolution is shown by the following equation.
ΔH = VT

For example, if the ship is sailing at 10 kt (10 x 1.852 km / h) and the transmission cycle is 0.1 seconds, ΔH = 0.5 m, and the horizontal resolution (measurement interval) is determined regardless of the depth measurement depth. be able to. As shown in FIG. 13, the resolution ΔH in the horizontal direction is determined only from the transmission cycle T and the ship speed V regardless of the depth. Further, the cases where six types of transmission signals can be identified are schematically shown in FIGS. 14 and 15. In this way, the transmission cycle T can be shortened, the depth can be measured regardless of the depth, and a high horizontal measurement resolution can be obtained.

Although the transmission signal can be identified by frequency or the like, if the frequency range used in the frequency discrimination method is widened, the propagation loss in water differs depending on the frequency, which is not preferable because the detection distance has a frequency difference. Since the improved acoustic measuring device identifies the transmitted signal by one frequency, such a problem does not occur. That is, since the transmission signal can be identified, the transmission cycle is not restricted to emit the next transmission signal after the echo of the seabed returns, and the sounding can be performed in a short transmission cycle, and the resolution in the horizontal direction can be improved. It can be dramatically improved.

The simulation results and actual measurement examples will be described with reference to FIGS. 16, 17, and 18. FIG. 16 shows a transmission signal and a reception echo signal (seafloor echo) obtained by a conventional echo sounder. The transmission cycle is 0.1 sec, and the echo of the seafloor appears around 0.07 sec. The depth of the transmission signal can be known by performing the next transmission after the echo is received and measuring the time from the transmission to the reception. In this case, if the speed of sound in water is 1500 / sec, a depth of (0.07 × 1,500 / 2 = 52.5 m) can be obtained.

On the other hand, in the echo sounding device using the improved sound measuring device, the transmission cycle can be determined regardless of the depth, and in the example of FIG. 17, the transmission cycle is 0.05 sec. The received echo signal on the seabed is obtained between the transmitted signals, but since the transmitted signals have identifiable code numbers A, B, C, ..., The received signals can be identified after passing through the correlator. .. Even a transmission cycle shorter than this example can be identified. Further, even if the transmission signal and the reception signal overlap, they can be identified.

For the actual received echo signal, compare the image of the conventional echo sounding device with the image of the echo sounding device using the improved echo sounding device. 18A and 18B are images of a conventional echo sounder. FIG. 18 compares the image of the conventional echo sounder with the image of the echo sounder by the improved echo sounder. FIG. 18A is a conventional image with a horizontal axis of 30 seconds, and FIG. 18B is an image with a horizontal axis of 3 seconds. In this example, the image is transmitted four times per second, and the horizontal axis is a considerably coarse image.

On the other hand, FIG. 18C is an image when the improved method of the acoustic measuring device is applied, the transmission cycle is set to 0.05 sec, and transmission is performed 20 times per second. FIG. 18D is an enlargement of a part of FIG. 18C. It can be seen that there is a considerably finer resolution in the horizontal axis direction as compared with FIG. 18B. The actual transmission signal when the transmission cycle is set to 50 times per second is as shown in FIG. A 200 kHz signal is phase-modulated with a 5th order 127-bit Gold Code with 4 waves as 1 bit, and pulse signals modulated with different Gold Codes are arranged and transmitted every 20 ms.

One pulse width Pd is expressed by the following equation, where the carrier frequency is fc, the number of waves used for one bit is N cycles, and the length of the Gold Code is M bits.
Pd = (1 / fc) × N × M

When the carrier frequency fc = 200 kHz, the number of waves used for one bit N = 4, and the length of the Gold Code M = 127, the pulse width Pd is as follows.
Pd = 1/20000 × 4 × 127 = 0.00254 = 2.54 msec

Even if the transmission cycle is further shortened and the two transmission pulses are transmitted so as to overlap each other, they can be separated after the correlation processing. FIG. 20 shows that even if two Gold Code signals (GC1 and GC2) are transmitted or received in an overlapping manner, the two Gold Code signals can be detected separately.

<2. Aperture synthesis>
Next, aperture synthesis will be described. Aperture synthesis is a method of increasing the resolution by forming a directivity equivalent to that of a transmitter / receiver with a long aperture by moving one transmitter / receiver. As shown in FIG. 21, it is a method of repeating transmission and reception while moving a transmitter / receiver of length d to obtain a horizontal resolution equivalent to that of a transmitter / receiver of length L, and is used as an aperture synthesis sonar. There is. To give a brief explanation, as shown in FIG. 22, the directional angle of the length L of the transmitter / receiver after aperture synthesis is sharper by the ratio d / L as compared with the directional angle of the length d of the transmitter / receiver. The resolution is improved.

In the coordinate system shown in FIG. 23, the composite signal S (x, y) of the reflected signal from the position of P (x, y) can be expressed by the following equation.

Here, An is a directivity function, tn is the time required for the round trip to the target P, and if the speed of sound in water is c, it can be expressed by the following equation.

It will be explained using computer simulation that the resolution is improved by aperture synthesis. Assuming that the point target is located at the position shown in FIG. 24, the echo of this target becomes an arc-shaped image as shown in FIG. 25 in the conventional echo sounder or sonar. FIG. 26A is an enlarged image of a part for easy understanding, but this image adopts a method using an already improved acoustic measuring device, and transmits 20 times per second, that is, 100 on this image. It is a simulation image of the echo of one time.

If this image is processed using the technique of aperture synthesis, an image as shown in FIG. 26B can be obtained. FIG. 26C shows an enlarged part of FIG. 26B. As can be seen from FIGS. 26B and 26C, it can be seen that the point target can be detected with a resolution of about 0.1 m. As the conditions for aperture synthesis, the transmission cycle was 0.05 sec (20 times / sec), the moving speed of the transmitter / receiver was 2 m / sec, and the aperture length was 10 m.

Similarly, as shown in FIG. 27A, when the aperture synthesis method is adopted in the conventional method, the image is 5 times when the transmission cycle is once per second, the moving speed is 2 m / sec, and the aperture length is 10 m. Since only transmission is possible, there are only 5 received echoes. Therefore, even if aperture synthesis is performed, only a low resolution image as shown in FIG. 27B can be obtained.

FIG. 28 is an image when the two point targets are arranged 0.2 m apart. The two point targets cannot be separated before the aperture synthesis (FIG. 28A), but the two point targets are after the aperture synthesis (FIG. 28B). Can be separated. FIG. 28C shows an enlarged part of FIG. 28B.

Although the aperture synthesis method is an existing technique, the aperture synthesis technique can be effectively used by advancing the transmission cycle by using the technique of the improved acoustic measuring device. That is, in the conventional aperture synthesis method, as in the conventional echo sounding, the next transmission is performed after the received echo returns, so that the transmission cycle T when the maximum detection distance is R is as described above (2R). It is necessary to satisfy the relationship of / 1500 <T). Therefore, when the maximum detection distance is R = 500 m, (T> 2 × 500/1500 = 0.67 sec) must be set, so that the transmission cycle is usually 1 time / sec. On the other hand, if the method of the improved acoustic measuring device is used, the transmission cycle can be set without being restricted by the maximum detection distance, so that 20 times / sec can be set, and aperture synthesis can be effectively used. it can.

The advantages of the improved acoustic measuring device described above are as follows.
Conventional echo sounding devices and the like are restricted by the speed of sound waves in water, but improved acoustic measuring devices eliminate this restriction. The restriction on the speed of sound waves in water means that a conventional echo sounder or the like transmits a transmission signal, receives an echo signal from the seabed, and then transmits the next transmission signal.
When performing aperture synthesis processing with a conventional echo sounder or the like, the transmission cycle cannot be shortened due to such restrictions, so the only way to increase the received data in the aperture is to slow down the ship speed. If the technology of the improved echo sounding device is adopted, the transmission signal can be transmitted with a transmission cycle several times to several tens of times that of the conventional echo sounding device, so that when performing aperture synthesis, it is compared with the conventional technology. It is overwhelmingly advantageous.

Since the transmission cycle cannot be shortened due to the limitation of the sound wave speed, the received signal often has no correlation with the previous received signal, so it is difficult to improve the SN ratio by adding a plurality of received signals. On the other hand, in the improved acoustic measuring device, the transmission cycle can be dramatically shortened, so that there is a correlation between the signals before and after. Therefore, since the SN ratio can be improved by adding the received signals before and after, the received signal can be added even at a low transmission output, and the device can be miniaturized and the power saving design becomes possible.

Radar is known as a technology similar to that of fishfinders. Radar uses radio waves because it is a device used in the air. The speed of radio waves is 300,000 km / sec, which is 200,000 times faster than the speed of sound waves in water of 1.5 km / sec. Therefore, even if the detection range of the radar is set to 100 km, for example, the round-trip time of the radio wave of 100 km is 0.00067sec = 0.67 ms, and the transmission cycle can be 1 ms. That is, even if transmission is performed 1,000 times per second, it does not overlap with the received echo. On the other hand, when trying to detect the seabed of 1,000 m underwater, the received echo signal is returned after 1,000 × 2/1500 = 1.33 seconds, so the transmission cycle is about 1.5 seconds. With radar and echo sounder, there is a ratio of 1.5 seconds / 1 ms = 1,500 times to a realistic detection distance of 100 km and 1,000 m, and how the speed of sound waves is that of underwater acoustic equipment such as echo sounders. You can see if the transmission cycle is constrained. If an improved echo sounding device is used, this restriction can be eliminated and the transmission cycle can be dramatically shortened, so that an epoch-making echo sounding device or the like can be designed.

<3. Multibeam echo sounder ＞
A multi-beam echo sounder will be described as another example of the improved acoustic measuring device. As shown in FIG. 29, the multi-beam echo sounder has a directivity called a fan beam that is narrow in the traveling direction of the ship and wide in the left-right direction, and a transmission signal is transmitted from one transmitter. It is called a multi-beam echo sounder because it has a plurality of beams that are wide in the front-rear direction and narrow in the left-right direction so as to cross the transmission beam. FIG. 30 shows the configuration of a multi-beam echo sounder of another example of an improved acoustic measuring device.

Similar to the above, the transmission side configuration includes a transmission trigger generator 1, a Gold Code generator 2, a pulse modulator 3, a transmission amplifier 4, and a transmitter 5. Underwater ultrasonic waves are transmitted from the transmitter 5. The transmission signal is a signal having a transmission cycle of several Hz to several tens of Hz.

The receiver of the multi-beam echo sounder has a plurality of receivers 61 to 6N, unlike the receiver of the single-beam echo sounder. Receiving amplifiers 71 to 7N are connected to the receivers 61 to 6N, and correlators 81 to 8N are connected to the receiving amplifiers 71 to 7N. Correlator 81-8N
The output signal from is input to the beamforming circuit 11 for each gold code, beamforming is performed, and a plurality of received beams are formed.

The beamforming circuit 11 is a delay element of an analog delay circuit and an analog delay circuit to which the outputs of the correlators 81 to 8N are supplied, respectively, as described in, for example, US Pat. No. 4,159,462. It is a circuit including a delay selection matrix that gives a predetermined delay by selection and an adder circuit that adds the output of an analog delay circuit. The output of the beamforming circuit 11 is supplied to the display and / or recording device 10, and the time until the echo is received with respect to the transmission pulse is displayed and / or recorded, respectively. When an improved acoustic measuring device is applied to such a multi-beam echo sounder, the same effect as described above can be obtained.

<4. Embodiment>
An embodiment of the sway correction device according to the present invention will be described. As explained with reference to FIGS. 5 and 6, when the seabed (meaning the seabed) is measured by ultrasonic waves, the depth measured by receiving wave sway with respect to the reference sea level is larger than that of the true seabed. It gets deeper and shallower. FIG. 31 shows the seafloor measurement values obtained by measurement with respect to the actual seafloor when the period of the ship's sway due to the waves is 1 Hz and the vertical movement is +/- 1 m. The value measured by the echo sounder on the seafloor changes under the influence of shaking. When the ship is lifted by waves, the measured values are deeper than the actual seafloor depth (shown by the dashed line), and when the ship is sunk, they are shallow. In the example of FIG. 31, it can be seen that the measured depth data (solid line) is affected by the sway with respect to the true seabed (broken line). The result of the sway correction is shown in FIG. As shown in FIG. 32, as a result of removing the swaying component due to the wave, the true seabed can be almost detected. If the seafloor is relatively flat, wave sway can be seen as a change in depth. Since the echo sounding device described above can shorten the period of the transmitted signal, it is possible to detect the swaying component due to the wave. There is a shaking component other than the change in the vertical direction (change in depth), but since the detected shaking component also includes the shaking component, it is not necessary to treat the shaking component separately. From this point of view, in the present invention, the period of the transmitted signal is (2D / Vu) or less when the velocity of the sound wave in water is Vu and the depth is D, and is compared with the period of the swaying component. It is made to satisfy the sampling theorem.

In one embodiment of the present invention, the sway component is measured from the measured data by frequency separation based on the fact that the change in the sway component (for example, wave) is more severe than the change in the true depth of the object (for example, the seabed). The shaking is corrected by removing it. When the depth change is large compared to the change of the sway component, it is difficult to correct the sway by the embodiment of the present invention. In practice, the agitation correction according to one embodiment of the present invention can be applied in many cases except for extremely rugged reef areas.

An example of the frequency separation method is to Fourier transform the depth data of the seafloor, remove the sway component using a filter that removes the frequency domain considered to be the sway component, and then perform the inverse Fourier transform to obtain the true seafloor. Only similar components are regenerated. FIG. 33 is a flowchart showing the flow of this process.

Step ST1: Fourier transform the seafloor depth data. As a result of the Fourier transform, for example, as shown in FIG. 34, Fourier transform data including a sway component is obtained. The peak at the center of FIG. 3 is the frequency component of the true seafloor, and the small mountain near 1 Hz shows the frequency component of the sway caused by the wave.
Step ST2: Filter the Fourier transform data. That is, as shown by the broken line in FIG. 34, the process of removing the component of 0.5 Hz or higher is performed to remove the component of a small mountain near 1 Hz.
Step ST3: Inverse Fourier transform the filtered data. As a result, as shown by the solid line in FIG. 32, seafloor data close to the true undulations of the seafloor can be obtained. In actual application, the true seafloor depth can be obtained by predicting or measuring the wave component in advance and removing the frequency component.

Another example of the frequency separation method is to supply the seafloor depth raw data to the low-pass filter (or band-pass filter) 21 to remove the sway component, as shown in FIG. 35. The seafloor depth raw data includes the sway component and means the data before the sway correction. As the low-pass filter (or band-pass filter) 21, for example, a configuration of an FIR (Finite Impulse Response) filter can be used as shown in FIG. A digital filter having an IIR (Infinite Impulse Response) configuration may be used. In FIG. 36, input data is supplied to the series connection of the unit delay element Z, and the coefficients a0 to an are multiplied by the multipliers M1 to Mn on each of the plurality of samples taken out from the stages of the series connection. .. Output data yn is obtained by adding the outputs of the multipliers M1 to Mn by the adder AD. A digital filter having a desired frequency characteristic can be constructed by the coefficients a0 to an.

In FIGS. 37A and 37B, the seabed depth raw data obtained in a transmission cycle of 100 times per second is input to the low-pass filter (or band-pass filter) 21 and output from the low-pass filter (or band-pass filter) 21. An example of obtaining seabed depth data with sway correction is shown in. In FIGS. 37A and 37B, the solid line 22 shows the seafloor depth raw data, and the broken line 23 shows the seafloor depth data after sway correction. The sway correction provides data showing the true seafloor depth.

Yet another example of sway correction according to an embodiment of the present invention will be described with reference to FIG. 38. Depth data is recorded using the echo sounder of the present invention shown in FIG. 7. The recorded depth data is time and depth value data as shown in FIG. 38. In this example, it is the depth data obtained by transmitting 20 times per second. Of course, even finer depth data can be obtained by transmitting 100 times per second.

By inputting the obtained depth data into the batch processing flow shown in FIG. 33, the sway correction processing can be performed.

<5. Other embodiments>
In another embodiment of the present invention, the sway component is detected by a ship (which may be a buoy) that is stationary and floating on the sea surface, and the sway component is detected to perform sway correction in near real time. As shown in FIG. 39, when the depth observation research vessel 31 navigates at a predetermined course and speed, the vessel 32 for detecting the sway component is stationary in the sea area affected by waves almost the same as the research vessel. Make it float. The agitation component detected by the ship 32 is wirelessly transmitted to the research vessel 31. In the research vessel 31, the agitation correction is performed by the agitation component received from the vessel 32.

As shown in FIG. 40, the ship 32 is provided with a transmitter 41 that sends ultrasonic waves to the seabed and a receiver 42 that receives echoes from the seabed. The shaking detection unit 43 is connected to the transmitter 41 and the receiver 42. The sway detection unit 43 obtains depth data as shown in FIG. 7 by the same configuration and signal processing as the depth measurement described above. This depth data should be constant because the ship 32 is stationary at the same place, but since it moves up and down due to the waves, it is only the data of the sway component. The sway data is supplied to the wireless communication unit 44, and the transmission data including the sway data is transmitted to the research vessel 31.

The research vessel 31 is provided with an echo sounding device similar to the depth measurement described above, as shown in FIG. FIG. 40 shows only some configurations related to sway correction. The depth raw data received by the receiver 6 and output from the receiving amplifier 7 is supplied to the low-pass filter or the band-pass filter 48. The sway data from the ship 32 is received, and the sway data is output from the wireless communication unit 45. The sway data is supplied to the adjustment circuit 46.

The adjusting circuit 46 Fourier transforms the sent sway data, detects the frequency component of the sway caused by the wave, and forms a control signal based on the detection result. The control signal controls the cutoff frequency of the low-pass filter or the band-pass filter 48 so as to remove the frequency component of the sway component. This control signal is supplied as a control signal of the cutoff frequency of the low-pass filter or the band-pass filter 48. This makes it possible to perform sway correction in near real time.

In another embodiment of the present invention, the sway correction is performed using the sway data actually detected, so that the accuracy can be improved. In addition to the research vessel, a ship for detection, a buoy, etc. are required, but the cost can be reduced by sharing the ship for detection, the buoy, etc. with multiple research vessels. In addition, the echo sounding device of the ship for sway detection has the same configuration as the echo sounding device of the research vessel, and it is easy to switch the roles of the ship and the research vessel for sway detection. It is possible to reduce the cost by devising.

<6. Application example>
In the present invention, there is one that transmits and receives ultrasonic waves using a transducer composed of an ultrasonic vibrator array. The transmitting beam is radiated from the ship toward the seabed in a fan shape, and the seabed is viewed through the receiving beam. As a result, the seabed where the transmitted beam range and the received beam range overlap is examined. In the multi-beam method, the strength of the ultrasonic echo for each azimuth can be estimated by forming a receiving beam having a predetermined beam pattern so that the main beam is directed to that azimuth for each azimuth. The present invention can be applied to the sway correction in such a multi-beam method.

<7. Modification example>
Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical idea of the present invention are possible. For example, the configurations, methods, processes, shapes, materials, numerical values, etc. given in the above-described embodiments are merely examples, and different configurations, methods, processes, shapes, materials, numerical values, etc. may be used as necessary. May be good. For example, when performing correlation detection, it is also possible to demodulate the received echo signal into a code and then detect the correlation. Further, although the echo sounding device has been described in the above description, the present invention can be applied to a device using an echo sounding technique such as a multi-beam echo sounding device, a side scan sonar, a fish finder, and a scanning sonar. .. Furthermore, the present invention can be applied not only to waves on the sea but also to sway correction of an echo sounder in fresh water.

The function of the processing device in the above-described embodiment can be recorded as a program on a recording medium such as a magnetic disk, a magneto-optical disk, or a ROM. Therefore, the function of the acoustic measuring device can be realized by reading this recording medium with a computer and executing it with an MPU (Micro Processing Unit), a DSP (Digital Signal Processor), or the like.

1 Transmission trigger Pulse generator 2 Gold code generator 3 Pulse modulator 5 Transmitter 6 Receiver 8 Correlator 10 Display and / or recording device 21 Low-pass filter or band-pass filter SR Shift register EXA1 to EX127 Calculation circuit

Claims (2)

An echo sounder that is installed on a moving body that moves on a swaying water surface and detects an object to be measured in water.
A transmission signal forming unit having a pseudo noise series generation circuit that generates a pseudo noise series signal and a modulation circuit that modulates a carrier signal with the pseudo noise series signal to form a transmission signal.
A transmission unit that periodically transmits the transmission signal as ultrasonic waves toward the measurement target located below the moving body, and a transmission unit.
A receiving unit that receives an echo caused by the ultrasonic waves transmitted from the transmitting unit being reflected by the measurement target, and a receiving unit.
A correlator that discriminates the echo corresponding to the transmission signal by performing correlation processing on the echo with the pseudo noise sequence signal.
A sway correction unit that suppresses the sway component by performing sway correction on the depth raw data corresponding to the time difference between the transmission signal and the echo.
It is provided with a display device for displaying a signal obtained by detecting the output signal of the correlator in which the sway component is suppressed in synchronization with the transmission signal.
The display apparatus displays the outgoing line extending in a substantially horizontal direction of the upper on the screen, the displays an signal detecting the output signal of the correlator with a color, the corresponding respective transmission timings adjacent test Display the wave signals in order,
The period of the transmission signal is (2D / Vu) or less when the velocity of the sound wave in water is Vu and the depth is D, and the period of the transmission signal is set to be less than or equal to (2D / Vu) and satisfies the sampling theorem as compared with the period of the shaking component. Echo sounder. In a multi-beam echo sounder that is installed on a moving body that moves on a swaying water surface and detects an object to be measured in water.
A transmission signal forming unit having a pseudo noise series generation circuit that generates a pseudo noise series signal and a modulation circuit that modulates a carrier signal with the pseudo noise series signal to form a transmission signal.
A transmission unit that periodically transmits the transmission signal as ultrasonic waves toward the measurement target located below the moving body, and a transmission unit.
A receiving unit that receives an echo caused by the ultrasonic waves transmitted from the transmitting unit being reflected by the measurement target, and a receiving unit.
A correlator that discriminates the echo corresponding to the transmission signal by performing correlation processing on the echo with the pseudo noise sequence signal.
A sway correction unit that suppresses the sway component by performing sway correction on the depth raw data corresponding to the time difference between the transmission signal and the echo.
It is provided with a display device for displaying a signal obtained by detecting the output signal of the correlator in which the sway component is suppressed in synchronization with the transmission signal.
The display apparatus displays the outgoing line extending in a substantially horizontal direction of the upper on the screen, the displays an signal detecting the output signal of the correlator with a color, the corresponding respective transmission timings adjacent test Display the wave signals in order,
The period of the transmission signal is (2D / Vu) or less when the velocity of the sound wave in water is Vu and the depth is D, and the period of the transmission signal is set to be less than or equal to (2D / Vu) and satisfies the sampling theorem as compared with the period of the shaking component. ,
A multi-beam echo sounding device that transmits a large number of ultrasonic beams in a fan shape by the transmitter.