JP2018159696A - Echo sounding device and echo sounding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a ghost when transmitting and receiving a transmission signal in a short cycle by eliminating constraint due to a velocity of an ultrasonic wave.SOLUTION: An echo sounding device installed on a mobile body for detecting an underwater measurement object comprises: a transmission signal formation part having a pseudo noise series generation circuit and a modulation circuit for modulating a carrier wave signal by a pseudo noise series signal with a transmission timing to form a transmission signal; a transmission part for transmitting the transmission signal as an ultrasonic wave into water; a reception part for receiving a reception signal including a true echo, a ghost of the transmission signal and a ghost of the reception signal; a correlator for performing correlation processing of the reception signal by the pseudo noise series signal to measure a distance to the measurement object on the basis of a time difference between the transmission signal and the true echo; and a transmission cycle change circuit for changing a transmission interval of the transmission signal to prevent timings of the true echo and the transmission ghost from being overlapped with each other. When a velocity of an acoustic wave in water is Vu, and the distance to the measurement object is D, the cycle of the transmission signal is (2D/Vu) or less.SELECTED DRAWING: Figure 27

Description

  The present invention relates to an acoustic sounding device and an acoustic sounding method that can transmit a transmission signal in a short period without a restriction due to the speed of ultrasonic waves.

  Acoustic sounding technology in the ocean has been practiced for a long time, and as shown in Fig. 1, an ultrasonic pulse is emitted from an ultrasonic transducer and the sound wave is reflected from the target (sea floor), and the underwater sound is detected. The depth is measured using the propagation speed of the sound wave (approximately 1500 m / s). An acoustic sounding device using this principle has been commercialized for more than 50 years, and even today, depth measurement of the sea floor is performed using this principle. This technique called echo location has been used without change, in other words, without development.

  The principle is that if an ultrasonic pulse (for example, 1 ms pulse width) is emitted and the seabed is 500 m and the round-trip distance is 1000 m and the underwater velocity Vu is 1500 m / s, 1000 / Vu = 1000/1500 = 0.667 seconds. Because it returns, after receiving the echo, it emits an ultrasonic pulse again, and at the same time, the depth of the seabed at a different place is measured as the ship advances. In this way, it is called an acoustic sounding device that measures the depth of the seabed sequentially as a ship navigates and displays it on a liquid crystal screen as recording paper or an image (see, for example, Patent Document 1).

  Conventional acoustic sounding devices have taken sounding by controlling the transmission interval so that the next transmission is not performed before the received echo in consideration of the sound speed of ultrasonic waves in water. As shown in FIG. 2, a depth measuring device having only one beam is called a single beam depth measuring device, and a device that spreads a plurality of beams in a fan shape that has recently appeared is called a multi-beam depth measuring device (see, for example, Patent Document 2). The multi-beam sounding device can measure a wide range of depth at a relatively high density.

  When the depth is D, the transmission interval of transmission pulses is T, and (2D / 1500) <T, the time difference between the transmission pulse and the reception echo corresponds to (2D / 1500), as shown in FIG. The depth can be measured from this time difference. However, in the case of (2D / 1500) ≧ T, as shown in FIG. 3B, since the reception echo arrives after the transmission of the next transmission pulse, it is not known which transmission pulse the reception echo corresponds to. An incorrect depth is measured based on the time difference FD. Therefore, conventionally, the condition of (2D / 1500) <T was necessary.

If the transmission cycle cannot be shortened, the horizontal resolution of depth measurement 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 navigates at 10 kt (10 × 1.852 km / h) and the transmission cycle is 1 second, depth measurement data can be obtained only about every 5 m. To measure the seabed at a depth of 1,000m, the transmission cycle T must be (1,000 × 2) /1,500=1.33 seconds or more, but if the ship sails at 10 kt, it is 1.33. Since it has advanced 6.7 m after 2 seconds, the measurement resolution ΔH is 6.67 m. The multi-beam sounding device can measure a wide range of depth at a time, but the resolution of the ship's direction of travel is the same as that of a single beam.

  In the conventional acoustic sounding device, there was no method other than reducing the speed of the ship in order to increase the measurement resolution. Therefore, the conventional acoustic sounding device has a problem that the time required for sounding is long when the sounding resolution is increased.

  The inventor of the present invention has proposed an acoustic sounding device capable of solving such a problem. That is, the transmission signal is formed by the pseudo noise sequence signal, the echo of the ultrasonic wave is received, the echo is correlated with the pseudo noise sequence signal, the echo corresponding to the transmission signal is discriminated, and the transmission signal and the echo Obtain raw depth data based on the time difference. The cycle of the transmission signal can be (2D / Vu) or less when the velocity of the sound wave in water is Vu and the depth is D.

JP 2001-083247 A JP 2006-220436 A

  Although it is only necessary that the receiving unit can receive only true echo, in reality, there is a problem that ghosts of transmission signals and ghosts of reception signals are mixed, preventing accurate measurement.

  Accordingly, an object of the present invention is to provide an acoustic sounding device and an acoustic sounding method that enable accurate measurement by removing the influence of a ghost.

1st invention of this invention is installed in moving bodies, such as a ship, In the acoustic sounding device which detects the measuring object in water,
A transmission signal forming unit having a pseudo noise sequence generation circuit for generating a pseudo noise sequence signal and a modulation circuit for modulating a carrier wave signal by a pseudo noise sequence signal at a transmission timing to form a transmission signal;
A transmission unit for transmitting the transmission signal as ultrasonic waves into the water;
A receiver that receives a received signal including a true echo, a ghost of a transmission signal, and a ghost of a reception signal;
Correlator that measures the distance to the measurement object based on the time difference between the transmission signal and the true echo by performing correlation processing on the received signal with the pseudo noise sequence signal;
A transmission cycle changing circuit that changes the transmission interval of the transmission signal and prevents the true echo from overlapping the timing of the transmission ghost,
The period of the transmission signal is an acoustic sounding device in which the velocity of the sound wave in water is Vu and the distance to the measurement target is D, which is (2D / Vu) or less.
According to a second aspect of the present invention, there is provided an acoustic sounding method for detecting a measurement target in water by an acoustic sounding device installed in a moving body such as a ship.
A pseudo noise sequence signal is generated by a pseudo noise sequence generation circuit, a carrier signal is modulated by a pseudo noise sequence signal at a transmission timing, and a transmission signal is formed.
Send the transmission signal into the water as ultrasonic waves,
Receive the received signal including the true echo, the ghost of the transmitted signal, and the ghost of the received signal,
By performing correlation processing on the received signal with the pseudo-noise sequence signal by the correlator, the distance to the measurement object is measured based on the time difference between the transmission signal and the true echo,
Change the transmission interval of the transmission signal by the transmission cycle change circuit so that the true echo does not overlap the timing with the transmission ghost,
The period of the transmission signal is an acoustic sounding method in which the velocity of the sound wave in water is Vu and the distance to the measurement target is D, which is (2D / Vu) or less.

  According to the present invention, transmission ghosts and / or reception ghosts other than true echoes included in a received signal can be removed, and accurate measurement can be performed. In addition, the screen display can be easily viewed. In addition, the effect described here is not necessarily limited, Any effect described in this invention may be sufficient. Further, the contents of the present invention are not construed as being limited by the exemplified effects in the following description.

FIG. 1 is a schematic diagram showing the principle of acoustic sounding. FIG. 2 is a schematic diagram for explaining single beam depth measurement and multi-beam depth measurement. FIG. 3 is a waveform diagram used for explaining a conventional acoustic sounding device. FIG. 4 is a schematic diagram used for explaining the horizontal resolution of a conventional acoustic sounding device. FIG. 5 is a block diagram showing a configuration of a reference example of the present invention. FIG. 6 is a block diagram used for explaining the correlator in the acoustic sounding device. FIG. 7 is a waveform diagram used for explaining the output of the correlator. FIG. 8 is a schematic diagram illustrating a case where a received signal is displayed. FIG. 9 is a waveform diagram showing an example of a transmission signal modulation method. FIG. 10 is a waveform diagram used for explaining the acoustic sounding device. FIG. 11 is a timing chart of the seabed echo before ghost removal. FIG. 12 is a timing chart of the seabed echo after ghost removal. FIG. 13 is a block diagram of an example of a ghost removal circuit. FIG. 14 is a timing chart of the received signal after passing through the ghost removal circuit. FIG. 15 is a block diagram of another example of the ghost removal circuit. FIG. 16 is a timing chart used for explaining a method of generating a ghost replica of a transmission signal. FIG. 17 is a timing chart of the received signal after passing through the ghost removal circuit. FIG. 18 is a schematic diagram showing a display image of the acoustic sounding device. FIG. 19 is a schematic diagram showing a display image of the acoustic sounding device before ghost removal and a display image of the acoustic sounding device after ghost removal. FIG. 20 is a block diagram illustrating an example of a configuration for generating a ghost replica of a transmission signal. FIG. 21 is a timing chart for explaining a reception ghost removal method. FIG. 22 is a schematic diagram showing the difference in the appearance of seabed echoes when the period of the transmission signal is constant and when the period is varied. FIG. 23 is a timing chart used to explain conditions for preventing a received signal from overlapping a transmission ghost. FIG. 24 is a timing chart used to explain conditions for preventing a received signal from overlapping a transmission ghost. FIG. 25 is a timing chart for use in more specific description of conditions for preventing the received signal from overlapping with the transmission ghost. FIG. 26 is a timing chart used for explanation when the transmission cycle is shortened to prevent the ghost and the seabed echo from overlapping. FIG. 27 is a block diagram of a configuration to which a transmission cycle change calculation circuit is added. FIG. 28 is a flowchart showing a processing flow of the transmission cycle change calculation circuit.

Embodiments of the present invention will be described below. The embodiments described below are preferred specific examples of the present invention, and various technically preferable limitations are given. However, the scope of the present invention is not limited to the following description. Unless otherwise specified, the present invention is not limited to these embodiments.
The description of the present invention will be made in the following order.
<1. Reference example>
<2. Embodiment>
<3. Modification>

<1. Reference example>
FIG. 5 shows an electrical configuration of an acoustic sounding device according to a reference example for understanding the embodiment of the present invention. A transmission trigger generator 1 for generating a transmission trigger pulse of a pulse signal having a constant period is provided, and the transmission trigger pulse is supplied to a gold code generator 2 as a PN sequence generator and a display or recording device 10. The display and / or recording device 10 includes a display device such as a liquid crystal and / or a recording device such as a semiconductor memory and an arithmetic device for display or recording.

  The gold code generator 2 generates a gold code in synchronization with the transmission trigger pulse. A PN (Pseudorandom Noise) sequence such as an M sequence other than the gold code may be used. A 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.

  The output signal of the pulse modulator 3 is supplied to the transmission amplifier 4, and processing such as amplification is performed in the transmission amplifier 4. The output signal of the transmission amplifier 4 is supplied to the transmitter 5. Ultrasonic waves are sequentially sent from the transmitter 5 to the water. The echoes of the emitted underwater ultrasonic waves are sequentially received by the receiver 6. An integrated configuration may be used as the transmitter 5 and the receiver 6.

  The received data from the receiver 6 is supplied to the receiving amplifier 7, subjected to processing such as amplification, and then supplied to the ghost removal circuit 11. The ghost removal circuit 11 includes a subtracter 12 and a transmission ghost replica memory 13. In the subtracter 12, the transmission ghost replica from the transmission ghost replica memory 13 is subtracted from the received data from the reception amplifier 7. The ghost removal circuit 11 will be described in detail later.

  The output of the ghost removal circuit 11 is supplied to the correlator 8. The output of the correlator 8 is supplied to the detection circuit 9. A correlator 8 extracts a reception echo corresponding to the transmission pulse. The detection circuit 9 performs calculation for display (for example, A / D conversion). The output of the detection circuit 9 is supplied to the display and / or recording device 8, and the time until the echo is received for the transmission pulse is displayed and / or recorded, respectively.

  FIG. 6 shows the correlation detection process. The received echo signal is input in series to the 4064-step shift register SR. It is preferable to improve the S / N ratio by adding a plurality of reception echo signals before and after the shift register SR. Noise can be reduced by the addition processing, and a low transmission output can be achieved, which enables downsizing of the apparatus and power saving design. The shift clock for operating 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 twice or more the carrier frequency (20 kHz) can be used. The received echo signal is sampled at a frequency eight times that of the carrier signal by being supplied to the shift register SR.

  Arithmetic circuits EXA1 to EXA127 are provided in parallel to the shift register SR. Each of the arithmetic circuits EXA1 to EXA127 includes an exclusive OR circuit and an adder circuit (4064 circuit). The 4064 bits of the shift register SR are commonly supplied to the exclusive OR circuits of the arithmetic circuits EXA1 to EXA127.

  On the other hand, a gold code code G1 replica (replica is 4064 bits), a code G2 replica,..., A code G127 replica are supplied to the exclusive OR circuits of the arithmetic circuits EXA1 to EXA127, respectively. . The exclusive OR circuit outputs “0” if the two input bits have the same value, and outputs “1” if the two input bits have different values. The 4064-bit output of each exclusive OR circuit is added. In the addition, if the number of “1” is N, a signal having an amplitude of N is output. By taking negative logic, an output with a larger value can be obtained as the two inputs coincide. The addition outputs of the arithmetic circuits EXA1 to EXA127 are as shown in FIG. A large amplitude output indicates a received echo signal that matches the gold code of the transmitted pulse.

  FIG. 8 illustrates a case where display is performed on the display and / or recording apparatus 10. 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 with a color, for example. Since the transmission trigger pulse is a fast repetitive signal of several Hz to several tens of Hz, the detection signals corresponding to the transmission trigger pulses from the correlator 8 are displayed so as to be sequentially arranged, thereby comparing with the conventional acoustic sounding device. As a result, the depth measurement image appears several times to several tens of times faster.

FIG. 9 illustrates an example of pulse modulation. For example, the phase is switched between 0 and π in correspondence with the gold code bits “0” and “1” every four periods (four waves) of a 200 kHz carrier wave. The frequency of the carrier wave is an example, and other frequencies may be used, and a modulation scheme such as QPSK other than BPSK may be used. Further, not only phase modulation but also amplitude modulation may be used.

  Correlator 8 detects correlation by digital signal processing. One bit is composed of 4 periods, and each period 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).

  The improved acoustic sounding device described above can identify transmitted signals and received echo signals (seafloor echoes). As shown in FIG. 10, the transmission signal A and the transmission signal B are different gold codes. A reception echo signal corresponding to the transmission signal A is received after the transmission signal B, and it can be identified that the reception echo signal corresponds to the transmission A. Therefore, the restriction ((2D / 1500) <T) related to the transmission cycle T as in the prior art can be eliminated.

In the improved acoustic sounding device, the horizontal resolution is as shown in the following equation.
ΔH = VT

  For example, if a ship sails at 10 kt (10 × 1.852 km / h) and the transmission cycle is 0.01 seconds, ΔH = 0.05 m, and the horizontal resolution (measurement interval) is determined regardless of the depth of measurement. be able to. Regardless of the depth, the horizontal resolution ΔH is determined only from the transmission cycle T and the ship speed V. Thus, the transmission cycle T can be shortened, depth measurement can be performed regardless of the depth, and high horizontal measurement resolution can be obtained.

  Although the transmission signal can be identified by frequency or the like, in the frequency discrimination method, if the frequency range to be used is widened, propagation loss in water varies depending on the frequency, which is not preferable because a frequency difference appears in the detection distance. In the improved acoustic sounding device, since the transmission signal is identified by one frequency, such a problem does not occur. In other words, since the transmission signal can be identified, there is no restriction that the next transmission signal is emitted after the echo of the seabed is returned as in the conventional transmission cycle, depth measurement is possible with a short transmission cycle, and the horizontal resolution is reduced. It can be improved dramatically.

  Next, the ghost removal circuit 11 of the reference example of the present invention will be described. FIG. 11A is a raw waveform of the transmission signal and the reception signal of the acoustic sounding device. In the example of FIG. 11A, the transmission interval is 10 msec, and the number of transmissions is 100 transmission signals and reception signals per second. By passing the raw waveform through the correlator shown in FIG. 6, a waveform after correlation processing as shown in FIG. 11B is obtained.

  In the case of the waveform after the correlation processing, a transmission ghost (referred to as a transmission ghost) or a reception ghost (referred to as a reception ghost) appears in addition to the original submarine echo, which interferes with the measurement based on the target bottom echo There is. Therefore, the present invention eliminates the transmission ghost and the reception ghost that are obstructed.

  FIG. 12A shows the same waveform as FIG. 11A. FIG. 12B is a waveform after the transmission ghost signal is removed from the waveform of FIG. 12A. Since only the received signal remains after the transmission ghost signal is removed, if the waveform is subjected to correlation processing, a waveform as shown in FIG. 12C is obtained. Although a ghost of the transmission waveform is expected to remain slightly, the influence of the ghost is affected. A small received signal can be obtained.

  The ghost elimination circuit 11 and the correlator 8 are shown in FIG. As shown in FIG. 13, the ghost removal can be performed by subtracting the transmission signal ghost replica waveform stored in advance from the output signal of the reception amplifier 7 in the deceleration point circuit 12. If the signal after the ghost removal from the subtraction circuit 12 is subjected to correlation processing by the correlator 8, a signal from which the ghost has been removed can be obtained.

FIG. 14A shows the raw waveforms of the transmission signal (TXGC1, TXGC2, TXGC3,...) And the reception signal (RXGC1, RXGC2, RXGC3,...). FIG. 14B shows a ghost replica of the transmission signal. This is an output signal of the subtraction circuit 12. Two examples (waveform 1 and waveform 2) of the waveform after the correlation processing by the correlator 8 are shown in FIG. 14D.

The ghost removal process can be performed not only before the correlation process but also after the correlation process. As shown in FIG. 15, the transmission signal ghost replica after correlation processing is stored in the transmission signal ghost replica memory 14. The subtraction circuit 15 ₁ , 15 ₂ ,..., 15 ₁₂₇ subtracts the corresponding transmission signal ghost replica from the signal after correlation processing from the correlator 8 to perform ghost removal processing.

A method of generating a transmission signal ghost replica will be described with reference to FIG. The transmission signal shown in FIG. 16A is input to the correlator, and 127 types of correlation output signals (G1replica, G2replica,... G127replica) shown in FIG. 16B become ghost replica signals. These ghost replica signals are stored in the transmission signal ghost replica memory 14.

  FIG. 17 is a waveform diagram showing processing for removing a transmission signal ghost. FIG. 17A is a raw waveform of the transmission signal and the reception signal of the acoustic sounding device. FIG. 17B shows the output obtained by outputting this raw waveform to the correlator 8, for example, the G1 signal output. FIG. 17C shows a corresponding transmission signal ghost replica G1 replica stored in the transmission signal ghost replica memory 14.

By subtracting the transmission signal ghost replica G1 replica by subtracting circuit 15 ₁ from G1 signal output, as shown in FIG. 17D, the received signal after ghost removal is obtained. Similarly, the ghost can be removed with respect to the outputs of the other correlators 8. FIG. 17D shows a signal after ghost removal relating to the G1 signal output and a signal after ghost removal relating to the G2 signal output.

  The above-described ghost removal circuit shown in FIG. 15 has a larger memory scale and circuit scale than the ghost removal circuit (FIG. 13) that performs ghost processing before the above-described correlation processing. In addition, there is. Further, if the ghost removal processing before and after the correlation processing is performed together, the ghost removal effect can be further increased.

  FIG. 18 is an example of a display image of the acoustic sounding device when ghost removal processing is not performed. The horizontal axis of the screen shows time, and the vertical axis shows water depth. Fig. 4 shows a received signal including a ghost that causes a display on the side of the screen. This received signal includes the following signals in order, each causing a display on the screen. For example, the number of transmissions is 50 times / second.

Transmission signal TXGC1: Sea level (water depth 0m)
True received signal RXGC1: Display E of true seafloor echo (wave that swells at about 70m depth)
Ghosts of transmission signals TXGC2 to TXGC6: transmission ghosts G2 to G6 corresponding to the transmission signals TXGC2 to TXGC6 (appearing in a straight line every 15 m)
Ghosts of reception signals RXGC124 to RXGC127: reception ghosts GE124 to GE127 (ghosts of seabed echoes) corresponding to the ghosts, respectively.

  Here, assuming that the ghost can be removed, it is possible to obtain a very easy-to-see image as can be seen by comparing the display image before ghost removal shown in FIG. 19A and the display image after ghost removal shown in FIG. 19B. FIG. 19 is an image (FIG. 19B) obtained when ghost removal is performed on an image (FIG. 19A) obtained by an experiment in an actual sea.

  An example of a transmission ghost replica generation method will be described with reference to FIG. Components corresponding to those in FIG. 5 are given the same reference numerals. The transmitting transducer 5 and the receiving transducer 6 are housed in an anechoic water tank 21 containing water. The reason why the anechoic water tank 21 is used is that an unnecessary reception signal is not generated. Then, normal acoustic sounding is performed, and the reception signal corresponding to the transmission signal is stored in the transmission ghost replica memory as a transmission ghost replica. Instead of the anechoic water tank 21, transmission and reception may be performed in a deep sea where no reception echo appears, and a transmission ghost replica may be obtained in the same manner.

  Since the ghost appears in the received signal, it is necessary to remove the ghost from the received signal. FIG. 21 shows an example of a method for removing ghost from a received signal. FIG. 21A is a raw waveform of a transmission signal and a reception signal. FIG. 21B shows one signal output when the received signal after transmission ghost elimination is processed by the correlator 8. When only a signal having a sharp peak is extracted from the waveform of FIG. 21B, the result is as shown in FIG. 21C. Similarly, other signal outputs of the correlator 8 and the waveforms extracted therein are shown in FIGS. 21D and 21E, respectively.

  As shown in FIGS. 21B to 21E, the received signal after the correlation processing has a clear difference between the true echo and the ghost echo. That is, a true echo has a waveform with a sharp peak, whereas a ghost echo has a waveform without a sharp peak. Therefore, the ghost removal of the received signal can be performed by a method in which only the waveform having a sharp peak is left after the correlation processing and other signals are erased.

<2. Embodiment>
Next, an embodiment of the present invention will be described. In one embodiment, the transmission cycle is changed so that the transmission ghost and the reception signal do not overlap. That is, this is a method of adjusting the transmission cycle so that the transmission ghost and the reception echo do not overlap.

  An embodiment will be schematically described with reference to FIG. FIG. 22A shows a display image when the number of transmissions is 50 times / second. Transmission ghosts appear linearly at predetermined water depth intervals. In this case, there is a part where the sea bottom echo overlaps with the transmission ghost and it is difficult to recognize a part of the sea bottom echo. FIG. 22B is a display image when the number of transmissions is changed to 40 times / second at the position of the broken line. Since the transmission interval becomes longer, the interval between the water depths where the transmission ghost appears becomes larger, and there is no place where the seabed echo and the transmission ghost overlap to make it difficult to recognize a part of the seabed echo.

  First, assume that a seabed echo is captured during a transmission ghost at a transmission frequency of 50 times / second. When the seabed gradually deepens and the transmission ghost and the seabed echo are likely to overlap, the number of transmissions is changed from 50 times / second to 40 times / second so that the seabed echo and the transmission ghost do not overlap with each other. Can be caught. An algorithm for changing the transmission cycle will be described below.

  The conditions under which the correlation received signal does not overlap with the transmission ghost will be described with reference to FIG. FIG. 23A shows transmission signals (TXGC1, TXGC2, TXGC3,...) And reception signals (TXGC1, TXGC2, TXGC3,...) That are sequentially transmitted, and FIG. Signals are shown. A waveform having a sharp peak after correlation is a reception signal corresponding to the transmission signal. Indicate the parameters as follows.

Transmission cycle Tint = M (1 / sec)
Transmission interval Tdur = 1 / M (sec)
Distance to target Dist (m)
Underwater sound velocity c (m / sec)
Transmission pulse width Pwidth

  The condition for the reception signal not to overlap the transmission pulse is to change the transmission cycle so that the reception signal comes between the nth transmission signal and the (n + 1) th transmission signal. This is expressed by the following formula.

  nTdur + 2Pwidth <2Dist / c <(n + 1) Tdur-Pwidth

  FIG. 24A shows a gold code transmission signal having a transmission count of 50 times / second, for example, and FIG. 24B shows an output signal after correlation. 24A and 24B show a state where the reception signal RXGC1 corresponding to the transmission signal TXGC1 is very close to the ghost of the transmission signal TXGC4 (a state immediately before overlapping). As a result, the display of the seabed echo is very close to the display of the transmission ghost, so that the display of the seabed echo becomes difficult to see.

  Therefore, the number of transmissions is changed to 40 times / second by a user operation or automatically. FIG. 24C shows the changed gold code transmission signal, and FIG. 24D shows the output signal after correlation. In this way, the timing of the reception signal RXGC1 can be set between the third transmission signal and the fourth transmission signal, and the display of echoes on the seabed is easy to see.

  Specifically, the relationship between the transmission ghost when the seabed depth is 100 m under the following conditions and the correlation received signal was calculated. The parameters in this case are set as follows. FIG. 25 shows specific values.

Transmission cycle Tint = M (1 / sec) = 50 times Transmission interval Tdur = 1 / M (sec) = 20 msec
Distance to target Dist (m) = 100m
Underwater sound velocity c (m / sec)
Transmission pulse width Pwidth = 2.54ms
Transmission frequency freq = 200kHz

  The condition for the received signal not to overlap the transmission pulse is expressed by the following equation. Since the time 2 Dist / c from transmission 1 to the target is 133.3 ms, the received signal from the target enters between the sixth transmission and the seventh transmission under the above conditions.

nTdur + 2Pwidth <2Dist / c <(n + 1) Tdur-Pwidth
= 6 × 20 + 2 × 2.54 <2 × 100/1500 <7 × 20−2.54
= 125.08 <133.3 <137.46

  In this example, when the received signal from the target exists between 125.08 ms and 137.46 ms, it can be seen that the transmission ghost and the received signal do not overlap.

  In the above description, the transmission ghost and the received signal are not overlapped by reducing the number of transmissions. However, conversely, the number of transmissions may be increased so that the transmission ghost and the received signal do not overlap. Alternatively, the number of transmissions may be increased or decreased. The example shown in FIG. 26 is an example in which the number of transmissions is increased so that the sea bottom echo and the transmission ghost do not overlap. In this example, as shown in FIG. 26A, the seabed is gradually becoming shallower, and the seabed echo and the transmission ghost are overlapped. As shown in FIG. 26B, the transmission ghost and the seabed echo are prevented from overlapping by increasing the number of transmissions and reducing the transmission interval immediately before the seabed echo and the transmission ghost are likely to overlap.

  FIG. 27 is a block diagram illustrating a configuration of an embodiment. It is the structure which added the transmission period change calculation circuit 16 with respect to the acoustic sounding device shown in FIG. FIG. 27 shows an example in which the ghost removal circuit 11 according to the reference example described above is provided, but the ghost removal circuit 11 is not necessarily provided. The transmission cycle change calculation circuit 16 is connected to the transmission trigger pulse generator 1 and is a circuit for changing the transmission cycle. The output of the signal detection circuit 9 is supplied to the transmission cycle change calculation circuit 16.

The operation of the transmission cycle change calculation circuit 16 will be described with reference to the flowchart of FIG. Initially, a default value of the number of transmissions, for example, 50 times / second is set (step ST1).
In step ST2 (determination A), it is determined whether or not there is a seabed echo during the transmission ghost. That is, it is determined whether or not a condition for preventing the reception signal indicated by the above-described mathematical formula from overlapping with the transmission pulse is satisfied. If the determination result is affirmative, 50 times / second is continued as it is.
If the determination result of step ST2 (determination A) is negative, the process proceeds to step ST3 (determination B).

  In step ST3 (determination B), as shown in FIG. 26, it is checked whether or not the water depth to be measured is gradually becoming shallower. If the determination result is affirmative, the process proceeds to step ST4. In step ST4, the number of transmissions is increased so that the received signal does not overlap with the ghost. If the determination result of step ST3 is negative, the process proceeds to step ST5 (determination C).

  In step ST5 (determination C), as shown in FIG. 22, it is checked whether or not the water depth to be measured is gradually increasing. If the determination result is affirmative, the process proceeds to step ST6. In step ST6, the number of transmissions is reduced so that the received signal does not overlap with the ghost. If the determination result of step ST5 is negative, the process proceeds to step ST1.

  The above-described processing is an example, and the determination for increasing or decreasing the number of transmissions may be reversed from the above description. In this case, the seabed echo and the transmission ghost intersect for a moment, but thereafter, the seabed echo comes between the transmission ghosts.

<3. Modification>
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, and the like given in the above-described embodiments are merely examples, and different configurations, methods, processes, shapes, materials, numerical values, and the like are used as necessary. May be. For example, the present invention is a multi-beam echo sounder, can be applied to aperture synthesis sonar.

DESCRIPTION OF SYMBOLS 1 Transmission trigger pulse generator 2 Gold code generator 3 Pulse modulator 5 Transmitter 6 Receiver 8 Correlator 10 Display and / or recording device 11 Ghost removal circuit 16 Transmission period change calculation circuit SR Shift register EXA1-EXA127 Operation circuit

This onset Ming is installed in the mobile, the echo sounder to detect the water to be measured,
A transmission signal forming unit having a pseudo noise sequence generation circuit for generating a pseudo noise sequence signal and a modulation circuit for modulating a carrier wave signal by a pseudo noise sequence signal at a transmission timing to form a transmission signal;
A transmission unit for transmitting the transmission signal as ultrasonic waves into the water;
A receiver that receives a received signal including a true echo, a ghost of a transmission signal, and a ghost of a reception signal;
The received signal have line correlation processing by the pseudo noise sequence signal, a correlator for generating an output signal as a large value when a pseudo noise sequence signal transmitted and received signals match,
A transmission period changing circuit that changes the transmission interval of the transmission signal and prevents the true echo from overlapping the timing of the ghost of the transmission signal ,
The period of the transmission signal is an acoustic sounding device in which the velocity of the sound wave in water is Vu and the distance to the measurement target is D, which is (2D / Vu) or less.
The present onset Ming, the echo sounder method for detecting the water measured by the installed sounder to the mobile,
A pseudo noise sequence signal is generated by a pseudo noise sequence generation circuit, a carrier signal is modulated by a pseudo noise sequence signal at a transmission timing, and a transmission signal is formed.
Send the transmission signal into the water as ultrasonic waves,
Receive the received signal including the true echo, the ghost of the transmitted signal, and the ghost of the received signal,
There line correlation processing by pseudo-noise sequence signal a received signal by the correlator to form an output signal which becomes a large value when a pseudo noise sequence signal transmitted and received signals match,
Change the transmission interval of the transmission signal by the transmission cycle change circuit so that the true echo does not overlap the timing of the ghost of the transmission signal ,
The period of the transmission signal is an acoustic sounding method in which the velocity of the sound wave in water is Vu and the distance to the measurement target is D, which is (2D / Vu) or less.

Claims (6)

In an acoustic sounding device that is installed on a moving body and detects a measurement object in water,
A transmission signal forming unit having a pseudo noise sequence generation circuit for generating a pseudo noise sequence signal and a modulation circuit for modulating a carrier wave signal by the pseudo noise sequence signal at the transmission timing to form a transmission signal;
A transmitter for transmitting the transmission signal as an ultrasonic wave into water;
A receiver that receives a received signal including a true echo, a ghost of the transmission signal, and a ghost of the reception signal;
A correlator that measures a distance to a measurement object based on a time difference between the transmission signal and the true echo by performing correlation processing on the received signal with the pseudo-noise sequence signal;
A transmission period changing circuit that changes a transmission interval of the transmission signal and prevents the true echo from overlapping the timing of the transmission ghost,
An acoustic sounding device in which the period of the transmission signal is set to (2D / Vu) or less when the velocity of the sound wave in water is Vu and the distance to the measurement target is D.   The acoustic sounding device according to claim 1, wherein the modulation circuit forms the transmission signal by phase-modulating a carrier wave with the pseudo noise sequence.   The acoustic sounding device according to claim 1, wherein a correlation is detected by data obtained by sampling the echo at a frequency twice or more of a carrier frequency and the pseudo noise sequence. In an acoustic sounding method for detecting an underwater measurement object by an acoustic sounding device installed in a moving body,
A pseudo noise sequence signal is generated by a pseudo noise sequence generation circuit, a carrier signal is modulated by the pseudo noise sequence signal at the transmission timing, and a transmission signal is formed,
Sending the transmission signal into the water as ultrasonic waves,
Receiving a received signal including a true echo, a ghost of the transmitted signal, and a ghost of the received signal;
Correlating the received signal with the pseudo-noise sequence signal by a correlator measures the distance to the measurement object based on the time difference between the transmission signal and the true echo,
By changing the transmission interval of the transmission signal by a transmission period changing circuit, the true echo does not overlap the timing with the transmission ghost,
The acoustic sounding method, wherein the cycle of the transmission signal is set to (2D / Vu) or less, where Vu is the velocity of sound waves in water and D is the distance to the measurement target.   The acoustic sounding method according to claim 4, wherein the transmission signal is formed by phase-modulating a carrier wave with the pseudo noise sequence.   The acoustic sounding device according to claim 4 or 5, wherein a correlation is detected by data obtained by sampling the echo at a frequency twice or more of a carrier frequency and the pseudo noise sequence.

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