A method for determining sonobuoy offset and system delay

Abstract

The present invention discloses a method for determining the offset distance and system delay of a sonar buoy, comprising: intercepting the sonar buoy data according to the source blasting time, obtaining the seismic profile before the system delay is corrected, identifying the direct wave, the seabed reflection wave and the seabed first-order multiple wave; obtaining the GPS coordinates of the source ship blasting point and the sonar buoy GPS coordinates, and obtaining the initial offset distance X; picking up the direct wave, the seabed reflection wave and the seabed first-order multiple wave, and obtaining the current track system delay and the corrected offset distance; finally replacing the initial offset distance with the corrected offset distance, and re-correcting the seismic track using the obtained system delay ΔT, that is, moving each seismic data forward by ΔT in time, that is, obtaining the seismic track after the system delay is corrected. This method can ensure the accuracy of seismic data processing, realize more accurate seismic imaging, and provide important technical support for the Antarctic and Arctic marine seismic exploration.

Description

Technical Field

[0001] The invention relates to the field of sonar buoy data processing, and in particular to a method for determining a sonar buoy offset and system delay. Background Art

[0002] Because of the low temperature all year round in the Arctic and Antarctic regions, the sea areas are covered with large areas of sea ice, which is characterized by large area, large thickness and strong fluidity. Even in the best navigation conditions in summer, the movement of floating ice is still the biggest obstacle to marine seismic exploration. Traditional single-channel and multi-channel seismic data acquisition equipment is difficult to work safely in the environment of moving floating ice.

[0003] Under such extremely harsh conditions, using sonar buoys for data collection is a feasible method. Unlike the mature towed cable collection system, the sonar buoy seismic acquisition system is still imperfect. Due to the separation of the source end and the receiving end of the sonar buoy acquisition, the two are independent acquisition systems. Due to the different systems, some key parameters, such as navigation positioning and system time, have large errors, resulting in serious errors in the later processing of seismic data, not to mention the later seismic imaging. Studies have found that the key parameters for using sonar buoy data to image the seabed stratigraphic structure include offset and system delay. These two parameters have been verified in practice to have large errors. Therefore, before sonar buoy imaging, the correct offset and system delay must be determined first.

[0004] The offset distance refers to the distance between the firing point and the receiving point. The firing point is located by the ship-borne navigation system, and the receiving point is located by the sonar buoy navigation positioning system. The Arctic and Antarctic regions are high-latitude areas, with a small number of satellites that can be received, large satellite elevation angles, and an active ionosphere. The ship-borne navigation system is relatively advanced and has a relatively high positioning accuracy, but the sonar buoy navigation system has poor positioning accuracy and may have a large error with the actual positioning position. In this case, the offset distance calculated directly using the positioning data of the two will have a large error.

[0005] System delay is caused by the inconsistency between the firing time and the sonar buoy time. Since the two belong to two different acquisition systems, the system time settings of the two are inconsistent, and the time is not completely unified through satellite timing. Even if the two are timed by satellite, the firing system is still a relatively complex integrated system, that is, the firing command still needs to convert the electrical signal into a mechanical signal, which still has a certain delay. If the influence of time delay cannot be eliminated, the data processing profile will have a certain error with the actual profile, and the data processing result is unreliable.

[0006] In summary, the determination of system delay and minimum offset is a key step in sonar buoy data preprocessing, and a deterministic result needs to be given, rather than simply copying the results of the field collection class report. Summary of the invention

[0007] The present invention aims at solving the technical gap in the prior art in determining the system delay and the minimum offset distance during the sonar buoy data preprocessing, and proposes a method for determining the sonar buoy offset distance and the system delay to ensure high-precision sonar buoy imaging.

[0008] The present invention is implemented by adopting the following technical solution: a method for determining the offset distance and system delay of a sonar buoy, comprising the following steps:

[0009] Step A, intercepting the sonar buoy data according to the source blasting time, obtaining the seismic profile before correction, and identifying the direct wave, the seabed reflection wave and the seabed first-order multiple wave;

[0010] Step B, obtaining the GPS coordinates of the source ship's firing point and the sonar buoy's GPS coordinates, and obtaining the initial offset distance X';

[0011] Step C, picking up the direct wave, the seabed reflected wave and the seabed first-order multiple waves, determining the current track system delay ΔT, and the corrected offset distance X;

[0012]

[0013] X=(T1-ΔT)*1.5

[0014] Wherein, T1 is the travel time of the picked direct wave, T2 is the travel time of the picked seabed reflected wave, and T3 is the travel time of the picked seabed first-order multiple waves;

[0015] Step D: Replace the initial offset X' with the corrected offset X, and move each seismic data forward by ΔT in time to obtain the seismic trace after system delay correction.

[0016] Furthermore, in step B, the initial offset X' is determined in the following manner:

[0017] X'=2*R*asin(sqrt(sa2*sa2+cos(lat1)*cos(lat2)*sb2*sb2))

[0018] Where X' is the initial offset; sa2 = sin((lat1-lat2) / 2.0); sb2 = sin((long1-long2) / 2.0); R is the radius of the earth; lat1 is the latitude coordinate of the source ship's firing point; lat2 is the latitude coordinate of the sonar buoy; long1 is the longitude coordinate of the source ship's firing point; long2 is the longitude coordinate of the sonar buoy.

[0019] Furthermore, in step C, the system delay ΔT and the corrected offset X are obtained by:

[0020] Assuming that the dip angle of the seabed stratum is small and the ray propagation conforms to the common center point assumption, the relationship between the direct wave travel time and the system delay and offset is constructed; at the same time, the relationship between the seabed reflection wave travel time and the system delay and offset as well as the relationship between the seabed first-order multiple wave travel time and the system delay and offset are established, as follows:

[0021] (T1-ΔT)*1.5=X

[0022]

[0023] Where D is the depth of the seabed;

[0024] The above equations are solved to obtain the system delay and the corrected offset.

[0025] Compared with the prior art, the advantages and positive effects of the present invention are:

[0026] This scheme creatively uses the travel time relationship between direct waves, seabed reflection waves and first-order multiple waves to determine the system delay and offset. By replacing the initial offset with the corrected offset, the seismic trace is recalibrated using the obtained system delay ΔT, and each seismic data is moved forward by ΔT in time to obtain the seismic trace after the system delay correction. This effectively ensures the accuracy of seismic data processing, achieves more accurate seismic imaging, and provides important technical support for marine seismic exploration in the Arctic and Antarctic. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of a seismic wave propagation path according to an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the sonar buoy data collection position according to an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of seismic data captured by the sonar buoy B0806 according to the blasting time in the embodiment of the present invention;

[0030] Figure 4 Schematic diagram of direct waves, seabed primary waves and seabed first-order multiple waves picked up by sonar buoy B0806 in embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram of a seismic profile after delay and offset correction of the sonar buoy system B0806 according to an embodiment of the present invention;

[0032] Figure 6 This is an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed below.

[0034] This embodiment discloses a method for determining a sonar buoy offset and system delay, such as Figure 6 As shown, the following steps are included:

[0035] Step A, intercepting the sonar buoy data according to the source blasting time, obtaining the seismic profile before the system delay is corrected, and identifying the direct wave, the seabed reflection wave and the seabed first-order multiple wave;

[0036] Step B, obtaining the GPS coordinates of the source ship's firing point and the sonar buoy's GPS coordinates, and obtaining the initial offset distance X';

[0037] Step C, picking up the direct wave T1, the seabed reflected wave T2 and the seabed first-order multiple wave T3, and obtaining the current track system delay ΔT and the corrected offset distance X according to the following formula;

[0038]

[0039] X=(T1-ΔT)*1.5 (2)

[0040] Wherein, T1 is the travel time of the picked direct wave, T2 is the travel time of the picked seabed reflected wave, and T3 is the travel time of the picked seabed first-order multiple waves;

[0041] Step D: Replace the initial offset X' with the corrected offset X, and recalibrate the seismic trace using the obtained system delay ΔT, that is, move each seismic data forward by ΔT in time, so as to obtain the seismic trace after the system delay correction.

[0042] Specific steps:

[0043] In step A, the data transmitted back by the sonar buoy by radio is intercepted according to the source shooting time, and the interception time length is generally set to 30s, to obtain the seismic profile before the system delay is corrected, and the obtained seismic profile is quality controlled. The direct wave, the seabed reflection wave, and the first-order multiple waves of the seabed are clearly identified in the profile. If the relevant effective waves cannot be identified, it is necessary to manually adjust the shooting time and the interception length until the above-mentioned effective waves can be correctly identified.

[0044] In step B, when obtaining the initial offset X', the following method is used:

[0045] X'=2*R*asin(sqrt(sa2*sa2+cos(lat1)*cos(lat2)*sb2*sb2)) (3)

[0046] Where X' is the initial offset; sa2 = sin((lat1-lat2) / 2.0); sb2 = sin((long1-long2) / 2.0); R = 6378137, which is the radius of the earth; lat1 is the latitude coordinate of the source ship's shot point, in radians; lat2 is the latitude coordinate of the sonar buoy, in radians; long1 is the longitude coordinate of the source ship's shot point, in radians; long2 is the longitude coordinate of the sonar buoy, in radians;

[0047] In step C, the travel time relationship between the direct wave, the seabed reflection wave (primary reflection wave) and the first-order multiple waves is mainly used to determine the system delay and offset. The principle is introduced as follows:

[0048] like Figure 1 As shown in the figure, when the dip angle of the seabed stratum is small, the ray propagation conforms to the common center point assumption, and the direct wave travel time has the following relationship with the system delay and offset:

[0049] (T1-ΔT)*1.5=X (4)

[0050] Where T1 is the travel time of the direct wave, ΔT is the system delay, and X is the offset distance;

[0051] The relationship between the travel time of the seabed reflection wave and the system delay and offset is as follows:

[0052]

[0053] Where T2 is the travel time of one wave, and D is the depth of the seabed;

[0054] The travel time of the first-order multiple waves on the seafloor has the following relationship with the system delay and offset:

[0055]

[0056] Where T3 is the travel time of the first-order multiple waves;

[0057] Among them, T1, T2, and T3 are known by picking travel time from seismic data. Solving the above three-variable quadratic equation system, we can obtain ΔT and X, that is,

[0058]

[0059] X=(T1-ΔT)*1.5

[0060] Then the system delay and corrected offset are obtained.

[0061] In step D, the corrected offset X is used to replace the initial offset X', and the seismic trace is recalibrated using the obtained system delay, that is, each seismic data is moved forward in time by ΔT, so that the seismic trace after the system delay correction can be obtained.

[0062] The method of the present invention is explained below using the sonar buoy data collected from the Arctic Ocean mid-ocean ridge as an example:

[0063] During the period from 2021 / 08 / 11 to 2021 / 08 / 31, seismic data collection was completed at two sonar buoys near the García Ridge in the Arctic Ocean. Figure 2 As shown in Figure 1. During this period, a total of 102 sonar buoy data with valid data were obtained. The sonar buoy data sent back by radio were intercepted according to the firing time of the source ship to obtain seismic data arranged according to the firing points. Typical data are as follows: Figure 3 Then, the initial offset is calculated based on the firing position obtained by the shipborne navigation system and the position obtained by the sonar buoy navigation system.

[0064] Due to the time delay between the airgun excitation time and the sonar buoy recording, the data start time is inconsistent with the excitation time. Figure 3 Taking the B0806 line as an example, according to the seawater seismic wave velocity of 1500m / s, the direct wave travel time curve can be obtained. The calculation formula is T = X' / V, where X' is the initial offset. Figure 3 It can be seen that the actual direct wave travel time is 17-20s, which is about 16s different from the theoretically calculated direct wave travel time, which shows that there is a large error in the system delay.

[0065] According to the method described in the embodiment of the present invention, the direct wave, the seabed primary wave and the seabed first-order multiple waves are picked up, such as Figure 4 According to formulas (1) and (2), the system delay and the corrected offset are calculated, and the corrected offset is used to replace the initial offset. Then, the obtained system delay is recalibrated to the seismic trace. After correction, Figure 5 As shown, it can be seen that the direct wave calculated theoretically is consistent with the actual collected data, which shows that the present invention has a high practical application effect and value.

[0066] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for determining sonar buoy offset and system delay, characterized in that: The following steps are involved: Step A, intercepting the sonar buoy data according to the source blasting time, obtaining the seismic profile before correction, and identifying the direct wave, the seabed reflection wave and the seabed first-order multiple wave; Step B, obtaining the coordinates of the firing point of the source ship and the coordinates of the sonar buoy, and obtaining the initial offset distance X'; Step C, picking up the direct wave, the seabed reflected wave and the seabed first-order multiple waves, determining the current track system delay ΔT, and the corrected offset distance X; X=(T1-ΔT)*1.5 Wherein, T1 is the travel time of the picked direct wave, T2 is the travel time of the picked seabed reflected wave, and T3 is the travel time of the picked seabed first-order multiple waves; Step D: Replace the initial offset X' with the corrected offset X, and move each seismic data forward by ΔT in time to obtain the seismic trace after system delay correction.

2. The method for determining sonar buoy offset and system delay according to claim 1, characterized in that: In step B, the initial offset X' is determined in the following manner: X'=2*R*asin(sqrt(sa2*sa2+cos(lat1)*cos(lat2)*sb2*sb2)) Where X' is the initial offset; sa2 = sin((lat1-lat2) / 2.0); sb2 = sin((long1-long2) / 2.0); R is the radius of the earth; lat1 is the latitude coordinate of the source ship's firing point; lat2 is the latitude coordinate of the sonar buoy; long1 is the longitude coordinate of the source ship's firing point; long2 is the longitude coordinate of the sonar buoy.

3. The method for determining sonar buoy offset and system delay according to claim 1, characterized in that: In step C, the system delay ΔT and the corrected offset X are obtained by: Assuming that the dip angle of the seabed stratum is small and the ray propagation conforms to the common center point assumption, the relationship between the direct wave travel time and the system delay and offset is constructed; at the same time, the relationship between the seabed reflection wave travel time and the system delay and offset as well as the relationship between the seabed first-order multiple wave travel time and the system delay and offset are established, as follows: (T1-ΔT)*1.5=X Where D is the depth of the seabed; The above equations are solved to obtain the system delay and the corrected offset.

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