JPS5861482A - Sonic prospecting device - Google Patents

Abstract

PURPOSE:To permit a sonic prospecting device, which investigates the geological structure of the bottom of the sea and deposits, to obtain invariably optimum sonic prospecting records on the basis of data programmed according to the conditions of the geological structure, by varying the characteristics of a filter, which selects a reflected wave received by a hydrophone, as a function of time. CONSTITUTION:A conversion part 40 consists of the 1st, 2nd, and 3rd D/A converters 41, 42, and 43 which convert a digital output from a control part 30 into analog signals, and is equipped with a voltage-frequency converter 44. This control part 40 controls characteristics of a TVG amplifier 51 and a TVF filter circuit 52 by analog signals. An analog signal S2 varies the center frequency (f0) of the TVF filter circuit 52 to 100-20Hz with time. Consequently, a reflected wave from the bottom of the sea which corresponds to the single-time acoustic wave emission of an air gun 12 is amplified by the TVG amplifier 51 on the basis of programmed data, and the TVF filter circuit 52 performs frequency selection to record data on the bottom of the sea on a graphic recorder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sonic exploration device that mainly investigates the geological structure and sediments of the ocean floor.

What is the situation on the ocean floor? :As a means of investigation, sound waves are emitted toward the ocean floor, and the data recorded by the reflected waves is used as an important source of information.

Figures 1 and 2 show a conventional seabed exploration method using sound waves and a block diagram of its equipment.
Near compressor4. An exploration ship equipped with a sonic exploration reception/recording device 5 and traveling on the sea Z; 2 is an air gun which is a sound source that instantaneously releases high pressure air compressed by the near compressor 4 into the sea, and generates a sound wave; Reference numeral 3 denotes a hydrophone that captures the sound waves reflected by the sending geological formation 6 from the Fgun 2 and converts them into electrical signals. Note that 7 indicates the sea level.

As shown in the block diagram of FIG. 2, the sonic exploration receiving/recording device 5 includes a drive pulse source 5a that triggers the air gun 2 at predetermined time intervals, an amplifier 5b that amplifies the signal received by the hydrophone 3, and a signal generator 5b that amplifies the signal received by the hydrophone 3. The bus filter 5C1 is composed of a graphic recorder 5d that records the intensity of the reflected wave and its delay time in synchronization with the driving pulse source 5a. Note that the sound source is not limited to the air gun 2 (sparkers, dynamite, etc.) may also be used.

A sonic exploration record is a continuous record of reflected waves from six layers of the ocean floor using a sonic exploration device having such a configuration. If you understand the characteristics of sound wave propagation, you can easily read the geological structure from sonic exploration records, so sonic exploration records are extremely important data in geological structure surveys, oil deposit exploration, and various other resource explorations. It has become.

However, such conventional sonic probes have the following problems.

1) Acoustic energy emitted from a sound source such as an air gun is attenuated by diffusion (proportional to the square of the distance) as it propagates deeper, and attenuated by absorption (attenuated by an exponential function of distance).
Therefore, the reflected wave becomes weak.

In other words, the reflected waves received by the iPhone at the sea surface are:
In general, the signal is strong in the seabed and the surface layer of the seabed, and the reflected signal in the sea and deep seabed is weak. Therefore, if the gain of the amplifier is high, the geological structure deep in the seafloor can be clearly recorded. However, the reflected waves from the seabed and shallow areas below the seafloor surface increase dramatically, causing signal distortion and saturation, making sonic survey records difficult to read.

On the other hand, if the gain of the amplifier is kept low, the structure of the deep seabed cannot be recorded, although the structure of the surface layer of the seafloor can be recorded with some degree of clarity.

2) The frequency components of the acoustic energy emitted by Fugan etc. range from approximately 10 Hz to 300 Hz, but high-frequency sound waves are severely absorbed and attenuated under the ocean floor.

Therefore, in the shallow part of the seabed, sound waves ranging from low to high frequency components are reflected, but the deeper the seabed, the more only the low frequency components penetrate, and the higher frequency components disappear. It turns out.

By the way, it is generally known that sound waves with high frequency components have good resolution as recorded data, but as mentioned above, in shallow areas under the ocean floor, reflected waves with high frequency components with good resolution are The reflected waves with low frequency components overlap and are masked, so fine details do not appear in the recording.

On the other hand, sound waves reflected from deep under the seabed are originally formed of low frequency components, but due to the reason 1) mentioned above, the reflected waves are extremely attenuated deep under the seabed. : Therefore, even if the gain of the amplification degree is increased, noise other than the reflected waves will be mixed in, resulting in recording with a poor S/N ratio.

In order to solve the above-mentioned problems in sonic exploration, conventional exploration equipment also uses AG C (Au
tmatic Ga1n Control)? :Additionally, or by using a means called compression that adjusts the gain using the charging and discharging characteristics of the capacitor,
The gain of the amplifier was adjusted, but the characteristics of such equipment were fixed and the gain could not be adjusted in response to changes in the geological structure, so it could not be said to perform a sufficient exploration function. .

This invention was made in view of this point, and it changes the characteristics of the filter that selects the reflected waves received by the hydrophone as a function of time, based on data programmed according to the situation of the geological structure. An object of the present invention is to provide a device that can always obtain optimal sonic exploration records.

An embodiment of the sonic exploration device of the present invention will be described below.

FIG. 3 shows a block diagram of the sonic exploration device of the present invention, in which numeral 11 is a driving pulse source that triggers the air gun 12, numeral 13 receives the above-mentioned reflected waves from under the seabed...
It's an hydrophone.

...The reflected wave received by the idrophone 13 is converted into an electrical signal and sent to the detection unit 20. and is input to the sound wave recording section 50.

The detection unit 20 includes a detection unit 21 that detects early reflected waves from the seabed from waves received by the hydrophone 13, and a first detection unit 21 that starts counting clock pulses based on the drive pulse of the air gun 12.
A second counter 22, 23, and a water depth memory 24 are also configured.

The sound wave recording unit 50 is a TVG (Time Variant).
ableGain ) amplifier 51, T V F (Ti
It is composed of a filter circuit 52 (Variable Filter) and a graphic filter 53, and
VG amplifier 51. 'The TVF filter circuit 52 has characteristics that change continuously as a function of time depending on the analog output signal of the converter 40, as will be described later.

The control unit 30 also includes an interface unit 31 for controlling data input/output, and a memory 32 . It is composed of a microprocessor 33 (hereinafter referred to as CPU) as the main part,
A display device 34, a printer 35, a dentizer 36, and an A-board 37 are provided as required.

The converter 40 converts the digital output output from the controller 30 into an analog signal. 2nd and 3rd D/
It is composed of A converters 41, 42, and 43, and further includes a voltage-frequency converter 44. A device,
TVG amplifier 51. This can be omitted if the TVF filter circuit 52 can be directly controlled by digital signals.

Next, the operation of the sonic probe according to the present invention will be explained with reference to FIG.

e in FIG. 4 indicates the trigger pulse Pt of the drive pulse source 11.
2 shows electric signals received by the hydrophone 13 from the emitted sound wave erad of the air gun 12 driven by the air gun 12 and the reflected wave e ref reflected from the seabed surface.

The detector 21 includes, for example, a level comparator, a bistable circuit, a launch circuit, etc., and receives the electric signal e.

When the initial vibration of the reflected wave eraf due to reflection from the seabed is detected, a detection pulse P, 111 is sent to the first counter 22. The first and second counters 22 and 23 have already counted the clock pulses CK of the reference oscillator (not shown) by the trigger pulse Pt.
stops counting by the detection pulse Pd, and outputs the calculated value t1 to the control unit 3 via the key face unit 31.
Enter 0.

The control unit 30 calculates tI by subtracting the time Δt from the previous count value t.
- Δt count value interface Uniso) 31'f! :
(In FIG. 4, the previous count value t is used as this count value.)

).

The second counter 23 is preset by the water depth memory 24 and is configured to generate a coincidence output with this counted value, so it outputs the start pulse P after counting the drop pulse CKYto-Δt. By doing so, it becomes possible to start the operation of the TVG amplifier 51 and TVF filter circuit 52, which will be described later, before the first seafloor reflected wave rises.

From this point on, the control unit 30 receives the start pulse P from the interface unit 31 and changes the gain characteristics of the TVG amplifier 51 and the TVF filter circuit, which are stored in the memory 32 as an array of 8-hint binary values, for example. 52 center frequency characteristics and bandwidth characteristics as digital signals, D2. D, when data is read out one after another at regular intervals, for example, every 16 mB for 4 seconds, 250×3 hide data is output from the memory 32 via the interface unit 31. The converter 40 converts the digital signal.

~D, as the first. Second. Third D/A converter 41°42.
43, the analog signal S,, S2. Convert to S3.

The analog signal S1 shown in FIG.
The analog signal S2 is the center frequency f of the TVF filter circuit 52.

over time from 100 Hz to 20 Hz K f
Indicates that the In addition, the TV adopted in this example
Since the center frequency characteristic of the F filter circuit 52 cannot be controlled by a voltage signal, the analog signal s2 is converted to the center frequency f by the voltage-frequency converter 44.

After converting the signal into an AC signal having the same frequency as that shown in FIG.

Finally, the analog signal S3 is shown in FIG. 4 changing from 11'c120Hz to 10Hz as time passes.

(Thus, the reflected wave from the seabed in response to one sound wave emitted by the air gun 12 is amplified by the TVG amplifier 51 based on the programmed data, further frequency-selected by the TVF filter circuit 52, and sent to the graphic recorder 53. It is recorded as ocean floor data.

By the way, the gain and frequency characteristics shown in Figure 4 indicate that the TV
The gain of the G amplifier 51 increases from a low gain of -10-I ThdB to 20 dB over time, and further increases gradually to 70 dB (on the other hand, the gain of the TVF filter circuit 52
The 0 frequency characteristic is initially the center frequency f. It has the characteristic of canting low-frequency signals with a bandwidth of 100 Hz and a bandwidth of 120 Hz, but as time passes, the center frequency gradually decreases. becomes low (and at the same time becomes a narrow band, allowing only limited low frequencies to pass through.

When the first recording operation ends in this manner, the second recording operation begins.

The second start pulse pH is 1.0 based on the count value t1 counted by the tenth counter 22 during the first recording operation. This occurs at −Δt and thereafter operates in the same manner as the first time.

The observer changes the data recorded by the graph recorder 53 (while observing the geological structure of the ocean floor) and changes the data programmed by the denotizer 36 and the keyboard 3T, and outputs the data to the TVG amplifier 51 and TVF filter circuit 52. It is possible to provide optimal characteristics for the geological structure under observation.

In addition, external storage devices such as floppy disks and PROM
It is also possible to store programs with a large number of different conditions as a data file and to immediately change the program 2 as necessary.

TVF filter characteristics generally have a center frequency f in the shallow part of the seabed. and the passband width B are controlled to be thick, and the center frequency f and the passband width B are controlled to be small, taking into account that there are many low frequency components in the deep part of the ocean floor. If the program is implemented, it will be possible to improve the resolution in the shallow part of the seabed and the S/N ratio in the deep part of the seabed.

FIG. 5(a) is a photograph showing a conventional sonic survey record, but when the TVF filter circuit 52 is used for the same geological structure, the conventional sonic survey record is shown as in the photograph shown in FIG. 5(b). Compared to the above, a more detailed geological structure can be read in the shallow part A of the seafloor.

It can also be seen that the S/N ratio has improved in the deep sub-seafloor part B, and the records have become clearer.

Although the sonic exploration device of the present invention has been described, T
The VG amplifier 51 and the TVF filter circuit 52 do not necessarily need to be programmed in conjunction, and the TVF filter circuit 52 of the present invention may be combined with an amplifier having a constant gain for the signal, like a conventional amplifier. Needless to say.

As explained above, in this invention, the bandpass characteristics of the TVF filter circuit are programmed according to the geological structure, so it is possible to record the geological structure in the shallow part of the seabed with high resolution. S/N of reflected signal
You can improve the ratio. Moreover, since the TVF filter circuit operates in real time, it is possible to analyze the geological structure during observation, making survey efficiency extremely high.

Moreover, the frequency characteristic of the TVF filter circuit is continuously at its center frequency f. and the passband width B can be made variable,
Moreover, since its control is programmable by using the CPU and memory, it has the advantage that the software is simple and the takes can be easily organized.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining conventional submarine sonic exploration, Fig. 2 is a block diagram of a conventional sonic exploration device, Fig. 3 is a block diagram of a sonic exploration device of the present invention, and Fig. 4 shows 12 in the figure. , 13 is a /% ID μphone, jLii device, 52 is a TVF filter circuit, and 53 is a graph recorder. Figure 5 (a) 1 1 1 1 1 1 1 l - River "[- + : + , I+ -, , :, +, -=
:It Figure 5(b) Procedural amendment (method) Date of March 1980 t Indication of the case Patent application No. 317 No. 1987 2 Name of the invention Sonic probe device 3 Person making the amendment Relationship with the case Patent applicant 1-3-1 IIgaseki, Chiyoda-ku, Tokyo 1t4I Director of the Agency of Industrial Science and Technology Makoto Ishizaka - France Designated agent 6 Subject of amendment Appropriate drawing 7 Contents of M Correct as attached Figure 5 (a) +1 ”, :, 1 .1 , “11 Ding 1
21-1 Spear 5 Diagram (b) Tsu, O Ceng Yuedan

Claims (1)

[Claims] In a sonic exploration device that consists of a device that oscillates sound waves, a device that receives reflected waves from strata, and a device that records the received waves, the frequency characteristics of the filter that selects the received waves correspond to the geological structure that is the object of exploration. What is claimed is: 1. A sound wave exploration device characterized in that the sound waves are variable based on programmed data.