JPS6259272B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is based on a ship that tows a towed receiver consisting of multiple channels, and a sound wave signal emitted from a sound source installed near the stern of the ship propagates through the seawater, and further transmits sound waves in the strata under the seabed. This is a geological exploration data signal processing method in which a signal reflected from a certain reflective layer is received by a towed receiver and the received signal is analyzed and processed, and particularly relates to a superimposition processing method that saves memory capacity.

Traditionally, this type of polymerization treatment method was generally CDP.
(Common Depth Point) Polymerization treatment was being carried out. As shown in Figure 1, this conventional superimposition processing method combines the sound source position in a shot at a certain time into one
1. The position of the towed receiver is 12, the propagation path of the sound wave reflected at a reflection point 17 in the stratum is 13, and the sound source position and towed wave reception when the ship moves after a certain period of time has elapsed. The propagation path of the sound wave reflected at a certain reflection point 7 is 14, respectively.
15 and 16, the towed received wave having the same reflection point 7 is selected from all the recorded data of several shots of the signals received by the channel of the receiver on the propagation paths 13 and 16 before and after the elapse of the above-mentioned fixed time. This selects the received channel data within the device and superimposes the received signals of each channel. In the figure,
Among the propagation paths, the path indicated by the dotted line indicates the path corresponding to the shot within the above-mentioned fixed time.

When this superposition process is performed under normal conditions, for example, if the sampling period for data recording is 4 msec, the reception recording time is 5 seconds, and the number of reception channels of the towed receiver is 12, the reception data for one shot is approximately 22.5 seconds. If CDP polymerization is performed by recording data for kilowords (1 word = 16 bits) and 12 shots, a huge memory capacity of about 270 kilowords is required, so the main memory alone is not enough, and the capacity is further increased. This requires a large magnetic disk, and since the received signal data of the channel to be processed spans several shots, real-time processing in which the data is not input to the processing device at once and is immediately combined is impossible.

For this reason, conventionally, the received signal data of each channel was recorded on a magnetic tape for each shot on board the ship, and later the data was merged using a large-scale computer on land using a magnetic disk or the like. Therefore, there are drawbacks such as the need for a hardware configuration with a large memory capacity such as a magnetic disk, the inability to perform polymerization immediately, and poor efficiency.

The present invention solves the above-mentioned drawbacks by merging only the received signal data obtained in one shot (common seafloor surface merging), and provides a geological exploration data merging process that instantly provides real-time merging results. It provides a method.

Next, an embodiment of the present invention will be described with reference to the drawings.

The common seafloor surface overlapping processing method first determines the reception position of each channel in the towed receiver based on the sound source using direct propagation waves from the sound source, and then combines this reception position with the water depth determined by an echo sounder, etc. The propagation time is determined by geometrically calculating the seafloor reflection propagation distance of each channel using the values, and then calculating the propagation distance assuming the underwater sound speed.

This propagation time indicates the time it takes for the signal emitted from the sound source to be reflected on the seabed and reach the receiving position of each channel in the towed receiver. It is continuously input after the plane reflected wave propagation time.

Therefore, the received signal of each channel is translated (delayed) by the time of the propagation difference so that the arrival time of the reflected signal is at the same position on the time coordinate axis, and the average between these received signal levels is Once the value is determined, it is possible to perform superposition processing on the stratum reflection signals normalized to the seafloor surface. This treatment is the common seabed surface polymerization treatment method.

FIG. 2 shows an example of applying the polymerization processing method according to the present invention, and is a schematic cross-sectional view when a reflected signal is received by a towed receiver in a channel. 21 is the sound source,
22 is a towed receiver, and this device has an N-channel receiver (channel 1 on the sound source side, channel N on the reflection side) built into the series, 23 is seawater, 24 is the seabed surface, 25 is the geological layer, 26 is any one reflective surface in the stratum, 27 and 28 are towing cables,
Reference numeral 29 indicates a signal processing device installed on board the ship.

As shown by the solid arrow line, the sound wave signal emitted from the sound source 21 propagates through the seawater 23 and reaches the seafloor surface 24, where part of it is reflected as shown by the dotted line and returns to the seawater 23, but the other part is refracted. The light propagates through the stratum 25 and reaches a certain reflective surface 26. The signal reflected from the reflective surface 26 follows the opposite path to reach the towed receiver 22.
Signals received on each channel from No. 1 to No. N of the towed receiver 22 are recorded in the signal processing device 29 via the towed cable 28.

Assuming that the reflecting surface 26 is horizontal, the sound wave propagation path takes a different path depending on the receiving device of the channel, and the larger the number of channels, the longer the path length and the propagation time. The dotted line in the figure shows the propagation path of the waves reflected from the ocean floor. Among the various reflected waves other than directly propagating waves, the reflected waves shown by this dotted line are received the fastest, followed by the reflected waves in the subsea layer. Received.

Therefore, now 1, N/2, N of the towed receivers 22
Taking each channel as a representative example, the received signal waveform is shown in FIG. In Fig. 3, the vertical axis shows the signal level V, the horizontal axis shows the propagation time T, and the origin shows the shot time, and a to c are 1 and N/C, respectively.
2. In the received signal waveform of the N channel, A to C indicate the signal portion of the reflected wave on the seafloor surface, and D to F indicate the signal portion of the reflected wave from a certain reflective surface in the stratum.

For each of channels 1, N/2, and N of the towed receiver, the propagation times T ₁ to _{T 3} of waves reflected from the seabed are determined as described above.

The overlapping processing method according to the present invention moves and delays signals B and C by the propagation time difference of the seafloor reflected waves so that the positions of signals B and C of each channel of the receiver overlap with the position of signal A. That is, the signals and C in FIG. 3 are respectively T ₂ -T ₁ and T ₃ - as shown in FIG.
It is delayed by T ₁ and moved to times B' and C', and the average value of each channel standardized in time with respect to the seafloor surface is determined.

Figure 4 a, b, and c show the received signals of the 1, N/2, and N channels of the receiver standardized with respect to the seabed surface, and A, B', and C' are the received signals of the seafloor reflected waves. Parts D, E', and F' indicate the received signals of reflected waves from reflective surfaces in the strata. The superimposition process according to the present invention is to obtain a (sum) value of the received signal levels shown in FIG. 4a, b, and c, that is, a common seafloor superimposition result shown in FIG. 4d. H and I on the diagram indicate the signals after the superposition processing of the superimposed seafloor reflected wave receiver part and the reflected wave receiver part in the geological formation, especially the reflected wave reception from the reflecting surface in the geological formation. No. I
It can be seen that this is more emphasized than when no polymerization occurs.

Strictly speaking, the polymerization treatment method according to the present invention does not polymerize at one point among certain reflective surfaces in the stratum, but the size of these reflective surfaces depends on the water depth,
Since it is small compared to the depth of the reflecting surface in the stratum, it can be regarded as approximately the same point, so by performing the above processing, the S/N ratio can be improved.

As explained above, the geological exploration data superimposition processing method according to the present invention performs processing using the received signal data obtained for one shot, so it does not require large-capacity memory such as a conventional magnetic disk. First, processing can be performed with a hardware-saving configuration using a main memory, and recordings with improved S/N ratios can be observed by performing online polymerization processing in real time after data input. Furthermore, since the recording can be monitored while data is being recorded, work efficiency is greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing a conventional polymerization treatment method, FIG. 2 is a conceptual diagram showing a polymerization treatment method according to the present invention,
3a to 4c and 4a to 4d are time charts for explaining the polymerization treatment method according to the present invention. 21... Sound source, 22... Towed receiver, 23...
Seawater, 24... Seabed surface, 25... Geological strata, 26...
One reflective surface in the stratum, 27, 28... Towing cable, 29... Signal processing device.

Claims (1)

[Claims] 1 In a multi-channel geological exploration data superimposition processing method using ultrasonic waves, the water depth value and the propagation time of reflected waves from the reception position of each channel to the seabed surface are calculated, and the predetermined value of the received signal data of each channel is calculated. 1 obtained by delaying the received signal of each channel by the time corresponding to each propagation time based on one data set, so that the arrival time of the reflected wave from the ocean floor is the same for each channel. A geological exploration data overlapping processing method characterized by overlapping processing of received shot data.