JP3530636B2 - Geological survey equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stratum exploration apparatus for emitting ultrasonic waves from a ship on the surface of water or an underwater towed body toward the bottom of the water, and knowing the stratum structure below the bottom of the sea from the display image of the echo.

[0002]

2. Description of the Related Art Generally, in this type of apparatus, a linear FM signal whose frequency increases linearly with time as shown in FIG. As shown in FIG. 2, pulse compression is performed by a pulse compression circuit that is a correlator to obtain a steep pulse. In addition, in FIG. 2 and subsequent drawings, each signal of a sine wave is drawn as a triangular wave for convenience of drawing.

FIG. 3 shows an outline of a conventional stratum exploration apparatus using such a correlator. 4 is a ROM, 5
The waveform of the LFM signal whose frequency rises from 5 KHz to 7.5 KHz during mS is stored as digital data. The digital LFM signal read from the ROM 4 is converted into an analog signal by the D / A converter 5,
The power is amplified by the amplifier 6 and supplied to the wave transmitter / receiver 8 via the transmission / reception switch 7. The echo signal obtained by this transmission is received by the transmitter / receiver 8, voltage-amplified by the amplifier 9 via the transmission / reception switching device 7, converted into a digital signal by the A / D converter 10, and then the correlator 11 Sent to.

The correlator 11 has an N-stage shift register for latching the received signal from the A / D converter 10;
Correlation waveform ROM that stores the same data as the waveform data of the LFM signal stored in OM4; signals read from each N-stage shift register, and read from the correlation waveform ROM corresponding to these read signals. N multipliers for multiplying the digital data thus generated; and an adder / full-wave rectifier unit for performing full-wave rectification by mutually adding signals from the multipliers.

The N-stage shift register is sequentially input from the right end in the figure from the head (5 KHz side) of the LFM signal according to a predetermined clock. Now, as shown in Figure 3, L
In the state where the FM signal is stored in the N-stage shift register for about half, the phases of both waveforms are deviated, so that the output from the adding / full-wave rectifying circuit is as shown by the side lobe S ₁ in the figure. The level is low. After that, when the LFM signal is stored in the N-stage shift register, the phase relationship of the LFM signals stored in both the N-stage shift register and the correlation waveform ROM matches, and at this point, the addition / full-wave rectifier The output is maximum, as shown by the main lobe M. On the other hand, when the first half of the LFM signal is out of the N-stage shift register, the output from the adder / full-wave rectifier is low as shown by the side lobe S ₂ , as in the state of FIG.

[0006]

The output data of the correlator in this case is shown in FIG. However, in FIG. 4, only the right half on the side lobe S ₂ side is shown. The side lobe S ₂ (same for S ₁ ) is detected at a level of −15 dB with respect to the main lobe M.

FIG. 5 shows the seabed image Q by the main lobe M, but when the side lobe S is derived, as shown in FIG. 6, the virtual image Z, Z'of the sea floor by the side lobe S. Also appears.

Therefore, measures have been taken to suppress the generation of the side lobes S. FIG. 7 shows the LFM signal stored in the ROM 4 of FIG. 3 and the correlation waveform ROM of the correlator 11, but instead of the constant amplitude (rectangular) LFM signal stored in the correlation waveform ROM, the amplitude at the center is changed. Is the maximum, and the amplitude value decreases in an arc shape toward both ends.
It is known that the generation level of the side lobes S can be reduced by using LFM signals of (amplitude 0 at both ends) and Hamming (having amplitude values at both ends). FIG. 8 shows output data of the correlator when the Hanning LFM signal is used for the correlation waveform ROM, and the side lobe S ₂ 'is -2.
The level was suppressed to 5 dB, but the level was not negligible, which hindered geological exploration.

Also, the LFM signal is 5.0 to 7.5K.
Although it was set to Hz, the optimum frequency range is an object to be searched (for example, a request to clearly display only the debris layer),
It changes depending on the stratum structure (whether the stratum is weak or not), the distance from the transducer to the water bottom, etc. Therefore, it is desirable to develop a device that can search using several different LFM signals without increasing the size of the device. Was there.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a stratum exploration apparatus capable of reducing the generation of side lobes to a level that can be ignored.

[0011]

Means for Solving the Problems The first invention (Claim 1)
The transmitter / receiver transmits an LFM signal whose frequency changes linearly during τ time, receives an echo of the LFM signal, and compresses the received LFM signal by pulse compression.
In a stratum exploration device that takes a correlation between the M signal and a signal that has the same frequency change as the LFM signal and whose amplitude value changes in an arc shape, and provides the correlation output as a display signal to both sides of the LFM signal to be transmitted. Further, by adding a signal of a predetermined width to form a single LFM signal, the side lobe generation level included in the correlation output is reduced.

[0012] The second invention (Claim 5), L frequency every τ time increases f ₁ ~f ₂ ~f ₃ ~f ₄ continuously as the ~
An LF for comparison in order to transmit the FM signal, receive the echo thereof, and perform pulse compression of the received LFM signal.
An n-system signal processing circuit that correlates with the M signal is provided, and in the first system, as the LFM signal for comparison, the frequency changes from f _{1 to} f ₂ and the amplitude value changes in an arc shape during τ. By using the signal, the received LFM signal in the first section of the frequencies f _{1 to} f ₂ is pulse-compressed, and in the second system, the frequency is f _{2 to} f ₃ during τ as the LFM signal for comparison. To the received LFM signal in the second section of the frequencies f _{2 to} f ₃ by using a signal whose amplitude value changes in an arc shape.
The received LFM signal in each of the first to n-th sections is individually pulse-compressed and used as display data for n screens.

[0013]

As shown in FIG. 3, when both LFM signals in the N-stage shift register and the correlation waveform ROM are not in phase, and the number N of multipliers is increased as much as possible, the output from the adder / full-wave rectifier Is statistically close to zero. However, the reason why the side lobes S are generated even at a low level is that the N value cannot be made large. Further, as shown in FIG. 3, for example, when the received signal is stored in the N-stage shift register only up to about half, the number of multipliers to be added becomes N / 2, which results in the side lobe S. The result is that the generation level of is increased.

Therefore, by adding the LFM signal before and after the LFM signal stored in the ROM 4 and having a pulse width of 5 mS and changing from 5 KHz to 7.5 KHz, the LFM signal stored in the correlation waveform ROM of the correlator 11 is more than the LFM signal stored in the correlation waveform ROM. If it is made long, even if the LFM signal in the 5 KHz to 7.5 KHz section is only partially stored in the N-stage shift register as shown in FIG. It can be seen that the output level of the side lobe S becomes smaller because the outputs from the N multipliers can be referred to.
The frequency of the LFM signal used in the present invention changes from low to high, but it may change from high to low.

In the first aspect of the invention, the L to be used for exploration is as described above.
Although the LFM signal is added before and after the FM signal to suppress the side lobe, in the second invention, the added LFM signal is also used as the search signal to search the same search target at a plurality of different frequencies. The signal enables geological exploration.

As a concrete constitution of the first invention, claim 2 is given.
The specific configuration of the second invention is shown in claim 6.

The pulse compression configuration according to the first aspect of the invention is applicable not only to the geological exploration device but also to various underwater exploration devices. Therefore, a third aspect of the present invention provides a "pulse compression circuit". I am charging.

[0018]

FIG. 9 shows a first embodiment of the first invention, and the same elements as those in FIG. 3 are designated by the same reference numerals. Reference numeral 1 is a pulse generation circuit that generates a clock pulse, and 2 is a trigger pulse generation circuit that outputs a trigger pulse when a predetermined number of pulses are input from the pulse generation circuit 1. A pulse counter 3 counts the pulses from the pulse generation circuit 1 and resets the count value when the trigger pulse is input.

The ROM 4 stores the LFM signal having a width of 15 mS, and as shown in the figure, it stores 2.5 K for each 5 mS.
The frequency rises from Hz to 5 KHz to 7.5 KHz to 10 KHz. That is, this LFM signal is obtained by adding an LFM signal having a width of 5 mS before and after the LFM signal that changes to 5.0 to 7.5 KHz during 5 mS shown in FIG. The ROM 4 reads the corresponding ROM data using the count value of the counter 3 as an address. The D / A converter 5, the amplifier 6, the transmission / reception switching device 7, the transceiver 8, the amplifier 9, the A / D converter 10, and the correlator 11 are the same as those described in FIG. However, the correlation waveform ROM of the correlator 11 has an LFM that changes to 5.0 to 7.5 KHz within 5 mS.
Although the signal is stored, the LFM signal is a Hamming signal whose amplitude value shown in FIG. 7 changes in an arc shape.

Reference numeral 12 is a delay circuit, which is an image memory 13
The supply timing of the count value supplied as the write address is delayed by the delay time (5 mS) of the signal received by the interposition device 11. In this case, the time point when the signal of 5.0 KHz which is the exploration signal is read from the ROM 4 is the transmission start time point T _1. However, if the time point when the signal of 2.5 KHz is read is the transmission time point, it is 5.0 KHz. Since the signal reading of ₅ ms after T ₁ , the delay circuit 1
The delay time at 2 is 10 mS. The image memory 13 is
The output signal of the interphase device 11 is stored as display data, and the display data is supplied to the display device 15. The delay circuit 12 is specifically a digital subtractor that subtracts the address value corresponding to the delay time from the count value. Although the write address is reduced as the compensating means here, it is also possible to write to the image memory 13 without delay compensation at the time of writing and operate the address at the time of reading data from the image memory 13.

As described above, even if the ROM 4 stores the LFM signal which changes in the range of 2.5 KHz to 5 KHz to 7.5 KHz to 10 KHz within 15 mS, this L
Among the FM signals, the interphase output signal becomes maximum when the LFM signal in the 5 KHz to 7.5 KHz section is stored in the N-stage shift register of the correlator 11, but as shown in FIG. 3, it is 5 KHz to 7.5 KHz. Even if the LFM signal of the interval is only partially stored in the N-stage shift register, the N-stage shift register here is full of data, so refer to the outputs from all N multipliers. Therefore, the generation level of the side lobe S becomes smaller.

The measurement results of the received signal for one transmission wave in this apparatus are shown in FIGS. 10 shows the measurement result from the beam center (0 mS) of the main lobe M ″ to 5 mS, and FIG. 11 shows the measurement result from 5 mS to 10 mS. As can be seen from these figures, the side lobe S ″ is It is significantly reduced to about −35 dB, and the side lobe level near the main lobe M ″ is particularly reduced as indicated by the arrow. The received signal related to this one transmission is the display 15 Vertical 1 pixel (or several pixels)
It becomes the display data of the column. L stored in the correlation waveform ROM
Even if the FM signal is a Hanning signal, the same effect can be obtained. Further, the LFM signal may have a frequency changing from high to low, and in that case, the ROM 4 stores 10 KHz to 7.5 KHz to 5.0 KHz to 2.5 KHz.
The LFM signal that changes as shown in FIG. 4 is stored, and the LFM signal that changes as 7.5 KHz to 5.0 KHz is stored in the correlation waveform ROM in the correlator 11.

In FIG. 9, the correlator 11 and the delay circuit 12 are used for the correlation processing and the time delay compensating means, but it is convenient to carry out these processing by the CPU, and FIG. 12 showing the second embodiment. The control block diagram is shown. A /
The received signal from the D converter 10 is stored in the signal memory 22 according to the address from the counter 3. The signal memory 22 is adapted to store signals for two waves, and while the signal related to one wave is being stored in the signal memory 22, the previously received wave signal is read out to the CPU 23.
In this manner, the binary counter 21 switches between writing and reading for each transmission. The CPU 23 is provided with a multiplication unit 23A and an addition / rectification unit 23B in order to program the same processing as the correlator 11 of FIG.
The data subjected to the correlation processing by the CPU 23 is the image memory 1
However, at this time, the time delay is compensated by subtracting the write address by the time required for the correlation processing in the CPU 23, and the write address is generated by performing such address operation. Part 2
It is 3C. The write address may not be manipulated, but the address at the time of reading data from the image memory 13 may be manipulated.

By the way, in FIG. 12 (same in FIG. 9),
The clock frequency for reading waveform data of 2.5 to 10 KHz from the ROM 4 is about twice the maximum frequency of 10 KHz, that is, 20 KHz is sufficient, but the clock frequency used for correlation processing is five times the maximum frequency. Since the above results are good, the clock frequency is 50KH.
z

Therefore, FIG. 13 shown as the third embodiment.
Then, using the 50 KHz pulse generation circuit 1 ',
Hz is supplied to the counter 27 as a clock for correlation processing, while the counter 3 is provided with the frequency divider 20 at 20 KH.
It is supplied after being divided into z.

Of the LFM signals stored in the ROM 4 of FIGS. 9, 12 and 13, those related to exploration are 5.0 to 7.5K.
It is a signal in the Hz section, and is 2.5 to 5.0 KHz and 7.
The LFM signal of 5 to 10 KHz contributes only to the side lobe level reduction. However, as described above, depending on the object to be explored, etc., 2.5 to 5.0 KHz
Alternatively, the LFM signal in each section of 7.5 to 10 KHz may be the optimum search frequency. Therefore, LFM of each section
FIG. 14 shows a first embodiment of the second invention of the present invention in which a signal is used for a search and an LFM signal of a plurality of different frequencies is simultaneously searched. In FIG. 14, elements common to those in FIG. 9 are given common reference numerals.

In the ROM 4, as shown in the figure, each 5 m
2.5 to 5.0, 5.0 to 7.5, 7.5 to 10, during S
It changes from 10 to 12.5KHz, and 2.5m during a total of 20mS.
The waveform data of the LFM signal changing from KHz to 12.5 KHz is stored. Then, in FIG. 9 (amplifier 9, A /
For the D converter 10, the correlator 11, the delay circuit 12), (9a, 10a, 11a, 12a), (9b, 10b, 11
b, 12b), (9c, 10c, 11c, 12c), (9d, 1
4 systems (0d, 11d, 12d). However, the correlation waveform ROMs of the correlators 11a to 11d have 2.5 to 5.0, 5.0 to 7.5, 7.5 to 1 respectively.
The LFM signal changing from 0 to 10 to 12.5 KHz is shown in FIG.
It is stored as the Hamming signal shown in. The delay times in the delay circuits 12a, 12b, 12c and 12d are 5 mS, 10 mS, 15 mS and 20 mS, respectively.
Reference numeral 14 indicates a desired screen from the four screens by the processing circuits of the above four systems on the display device 15, or the display device 15
Is a display control circuit for dividing the image into four and displaying four screens. A data recorder 16 records data in the image memory 13.

Here, the time point at which the 2.5 KHz signal is read from the ROM 4 is set as the wave transmission time point T _2, and therefore the delay time in the delay circuit 12a using the LFM signal in the 2.5 to 5.0 KHz section as the search signal. Is the correlator 11a
It is 5 mS required to pass through. On the other hand, the correlator 11
and 5mS delay for the passage of b, also because from transducer 8 of 5.0KHz of LFM signals of the second section is outputted becomes 5mS delayed the transmitting time point T _2, 5.0 to 7.
Delay circuit 1 using LFM signal in 5 KHz section as search signal 1
The delay time of 2b is 10 mS in total. For the same reason, the delay time in the delay circuits 12c and 12d is 15 mS, 2
It becomes 0 mS.

In the above-mentioned apparatus, the search video for the same search target is obtained by the processing circuits of four systems, and displayed on the display 15 as, for example, a 4-split screen. Since the search frequencies are different from each other, if there is a video in which the desired search target is displayed particularly clearly, that video may be selected and enlarged and displayed on the entire screen of the display unit 15. Note that the images obtained by the second and third processing circuits are those search signals (5.0 to 5.0).
LF on both sides of signals of 7.5 KHz and 7.5-10 KHz)
Since there is the M signal, the side lobe level is reduced as in the device of FIG. 9, but the search signals (2.5 to 5.0 KHz and 10 to 12.5 KHz in the first and fourth processing circuits are reduced.
Signal) has the LFM signal in only one of them, the side lobe level reduction effect is only one of the side lobe levels S _{1 and} S ₂ shown in FIG. If it is desired to obtain the effect of completely reducing the sidelobe level for the first and fourth processing circuits, 2.5 to 12.5KH
LFM signals may be added to both sides of the z LFM signal.

Also for the circuit configuration of FIG. 14, a CPU can be adopted for the correlation processing, and the configuration is shown in FIG. 15 which is the second embodiment of the second invention. Here, although the individual CPUs 23a to 23d are used for the processing circuits of the respective systems, a DSP (digital signal processor) is used.
If a high-speed calculation is possible, a single CPU can handle it. As in the case of FIG. 13, a high-speed clock different from the clock frequency for the counter 3 can be supplied to the circuit configurations of FIGS. 14 and 15 for correlation processing.

[0031]

EFFECTS OF THE INVENTION In the first aspect of the present invention, the LFM signal is added before and after the LFM signal used for exploration to make the signal width longer than that of the LFM signal for comparison. As a result, the generation level of the side lobes can be reduced, so that the virtual image due to the side lobes can be eliminated. The second invention is
Since the added LFM signal is also used as a search signal so that the same search target can be searched by a plurality of search signals of different frequencies, the optimum frequency in the search signal can be determined without increasing the size of the device. Even if it is unknown, the optimum image can be obtained from multiple screens.

[Brief description of drawings]

FIG. 1 is a diagram showing a frequency change of an LFM signal.

FIG. 2 is a diagram showing how an LFM signal is pulse-compressed by a correlator.

FIG. 3 is a block diagram of a geological exploration device equipped with a correlator

4 is an output data diagram of a correlator in the apparatus of FIG.

FIG. 5 is a diagram showing a seabed image by the main lobe of FIG.

FIG. 6 is a diagram showing not only the main lobe of FIG. 4 but also a sidelobe image of the seabed.

FIG. 7 is a waveform diagram of various LFM signals stored in a correlation waveform ROM.

8 is an output data diagram of a correlator when a Hamming signal is adopted for a correlation waveform ROM in the apparatus of FIG.

FIG. 9 is a block diagram of an underwater exploration device showing a first embodiment of the first invention.

FIG. 10 is a diagram showing a part of output data of the correlator of the correlator of FIG.

FIG. 11 is a diagram showing a part of output data of the correlator of the correlator of FIG.

FIG. 12 is a block diagram showing a second embodiment of the first invention.

FIG. 13 is a block diagram showing a third embodiment of the first invention.

FIG. 14 is a block diagram showing a first embodiment of the second invention.

FIG. 15 is a block diagram showing a second embodiment of the second invention.

[Explanation of symbols]

1 pulse generation circuit 2 Trigger pulse generation circuit 3 counter 4 ROM 5 D / A converter 6 amplifier 7 duplexer 8 Transceiver 9 amplifier 10 A / D converter 11 Correlator 12 Delay circuit 13 Image memory 14 Display control circuit 15 Indicator 16 Data recorder 21 binary counter 22 Signal memory 23 CPU 24 ROM 25 RAM 26 frequency divider 27 counter

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI G01S 15/89 G01V 1/00 C G01V 1/00 1/28 1/28 G01S 7/52 Z (56) References 2-20915 (JP, A) JP-A-3-242583 (JP, A) JP-A-8-313623 (JP, A) JP-A-3-231181 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01V 1/38 G01S 7/52 G01S 13/28 G01S 13/88 G01S 15/10 G01S 15/89 G01V 1/00

Claims (5)

(57) [Claims] 1. A transmitter / receiver transmits an LFM signal whose frequency changes linearly during τ time, receives an echo of the LFM signal, and pulse-compresses the received LFM signal.
In the stratum exploration device that takes a correlation between the received LFM signal and a signal that has the same frequency change as the LFM signal and the amplitude value changes in an arc shape, and uses the correlation output as a display signal, the LFM signal to be transmitted is A stratum exploration apparatus, wherein a generation level of a side lobe included in the correlation output is reduced by adding a signal of a predetermined width to both sides to form a single LFM signal. 2. A pulse generation circuit (1) for generating clock pulses; a counter (3) for counting clock pulses; and a trigger pulse generation circuit for resetting the count value of the counter (3) for each transmission. (2) and; ROM (4) that stores the data of the LFM signal whose frequency rises linearly during τ time and that uses the count value of the counter (3) as a read address; and ROM (4) A D / A converter (5) for converting data from digital to analog; an amplifier (6) for amplifying the signal from the D / A converter (5); and transmitting the LFM signal converted to analog A transmitter / receiver (8) for receiving the echo; and a transmission / reception switcher (7) for switching transmission / reception in the transceiver
And an amplifier (9) for amplifying the received LFM signal of the transmitter / receiver (8)
And an A / D converter (10) for converting the received LFM output of the amplifier (9) from analog to digital; and for pulse-compressing the received LFM signal output from the A / D converter (10) A correlation waveform ROM that stores, for comparison, a signal that has the same frequency change as the LFM signal stored in the ROM (4) and whose amplitude value changes in an arc shape, and a shift register that can latch a signal of τ time length A correlator (11) that correlates each data of the correlation waveform ROM with the received LFM signal sequentially input to the shift register.
An image memory (13) for storing the data of the correlation output of the correlator (11); and a received LFM signal for the count value supplied as an address for writing data to the image memory (13). A stratum exploration apparatus comprising: a compensating means (12) for compensating for a time delay caused by passing through a correlator (11); and a display (15) for displaying data of an image memory (13), wherein the ROM (4 ), A signal of a predetermined width is further added to both sides of the LFM signal to be stored as a single LFM signal, and the main output is obtained as a compressed pulse in the correlation output from the correlator (11). A stratum exploration device characterized by reducing the generation level of side lobes (S) derived from (M). 3. The stratum exploration device according to claim 2, wherein the CPU performs the correlation processing by the correlator (11) and the processing by the compensation means (12). 4. The stratum exploration device according to claim 2, wherein the compensation means (12) is a delay means for delaying the supply timing of the data write address value to the image memory (13). 5. The transmitter / receiver causes the frequency to rise during τ time.
The LFM signal that changes linearly is transmitted and
In order to pulse-compress the received LFM signal,
The received LFM signal and the same frequency change as the LFM signal
In addition, it correlates with a signal whose amplitude value changes in an arc shape,
The geological exploration device that provides the correlation output of
And the LFM signal to be transmitted has a predetermined length on both sides of the reference signal.
Included in the correlation output by making it a long LFM signal
It is characterized by reducing the level of side lobes generated.
Geological exploration device.