Straight optical fiber and spiral winding optical fiber combined near-earth surface wave exploration method
By combining straight and spiral-wound optical fibers in a near-surface wave exploration method, and utilizing fiber fusion splicing and inversion algorithms, the problem of axial sensitivity limitation of traditional straight optical fibers in complex environments has been solved, achieving high-precision near-surface velocity structure exploration.
Patent Information
- Application Number
- CN202511121092.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-12
- Publication Date
- 2025-11-18
AI Technical Summary
Traditional straight-fiber DAS suffers from axial sensitivity in complex environments, which limits the acquisition of surface wave information and leads to strong multiple solutions in dispersion curve inversion, making it difficult to achieve high-precision near-surface velocity structure exploration.
A near-Earth surface wave exploration method combining straight and spiral-wound optical fibers is adopted. By fusion splicing the optical fibers in series and combining the Haskell-Thomson matrix and the steepest descent inversion algorithm, a joint dispersion curve is constructed. Particle swarm optimization algorithm is used to avoid local minima, thereby improving computational efficiency and accuracy.
It achieves wideband, multi-mode dispersion curve inversion, improves the accuracy and reliability of near-surface shear wave velocity structure, and overcomes the multi-solution problem of traditional methods.
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Figure CN120972250A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of geophysical exploration, and particularly relates to a near-surface wave exploration method combining straight optical fibers and spiral-wound optical fibers. BACKGROUND
[0002] Near-surface structure exploration is of decisive significance for geological disaster early warning, resource exploration, major engineering site selection and urban underground space development, and the velocity structure directly affects seismic response analysis, foundation stability evaluation and shallow resource occurrence state judgment, and rich surface wave dispersion information is the basis for accurate dispersion curve inversion.
[0003] Traditional seismic exploration relies on densely arranged electronic geophone arrays, but faces significant limitations in complex environments such as urban dense areas, steep slopes and shallow seas. Distributed acoustic sensing (DAS) converts optical fibers into continuously distributed strain sensors, and a single optical fiber can achieve real-time monitoring with kilometer-level coverage and meter-level spatial resolution. However, conventional straight optical fiber DAS has axial sensitivity, and the obtained surface wave information is limited, resulting in strong multi-solution nature in dispersion curve inversion. SUMMARY
[0004] The purpose of the present application is to overcome the defects in the prior art. The near-surface surface wave exploration method combining straight optical fibers and spiral-wound optical fibers provided by the present application breaks through the axial sensitivity limitation of straight optical fibers and improves the accuracy of near-surface velocity structure exploration based on DAS by combining straight optical fibers and spiral-wound optical fibers.
[0005] To solve the above technical problems, the present application adopts the following technical scheme: a near-surface surface wave exploration method combining straight optical fibers and spiral-wound optical fibers, comprising the following steps:
[0006] S1: Based on straight optical fiber and spiral-wound optical fiber DAS seismic data acquisition and processing, design a straight optical fiber and spiral-wound optical fiber design observation system, simultaneously carry out active source excitation, respectively pick up straight optical fiber and spiral-wound optical fiber DAS active source seismic records of the same line, and carry out spatial homing of spiral-wound optical fiber DAS seismic records;
[0007] S2: Based on the joint of straight optical fiber and spiral-wound optical fiber surface wave dispersion curves, the multi-mode surface wave dispersion curves corresponding to the straight optical fiber and the spiral-wound optical fiber are obtained, and the dispersion curves obtained by the straight optical fiber and the dispersion curves obtained by the spiral-wound optical fiber are combined to obtain the joint dispersion curve;
[0008] S3: Based on the inversion of the joint straight optical fiber and spiral-wound optical fiber surface wave dispersion curves, the inversion objective function is constructed based on the Haskell-Thomson matrix method, and the shear wave velocity is inverted based on the deterministic inversion algorithm of the steepest descent method.
[0009] Furthermore, in step S1, the straight optical fiber and the spirally wound optical fiber are connected in series in the same optical path by optical fiber fusion splicing. The spirally wound optical fiber acquires richer surface wave information by changing the winding method of the optical fiber. Seismic data is synchronously acquired by combining the straight optical fiber and the spirally wound optical fiber to obtain seismic records. On this basis, the seismic records are preprocessed, including removing DC components, detrending, low-pass filtering, and downsampling. The removal of DC components and detrending are used to suppress the influence of low-frequency noise of the DAS instrument, and high-frequency noise is filtered out by low-pass filtering and downsampling, while reducing the data size and improving the computational efficiency.
[0010] Further, in step S1, straight fiber and spiral-wound fiber DAS seismic records of the same survey line are picked from the seismic records, and the spiral-wound fiber DAS seismic records are spatially repositioned to ensure that the offset of the straight fiber and spiral-wound fiber DAS seismic records in the observation coordinate system remains consistent:
[0011] x hwf =x sf ·sinα; (1)
[0012] In the above formula, x sf The straight fiber DAS channel spacing is α, where α is the winding angle of the helically wound fiber, and x is the angle of the helical winding fiber. hwf The spacing between DAS channels of helically wound optical fiber.
[0013] Further, in step S2, the dispersion spectra of the DAS shot gather records of the straight fiber and the spiral-wound fiber are calculated using the phase-weighted superposition method, respectively. The dispersion curves of the DAS shot gather records of the straight fiber and the spiral-wound fiber are then combined to obtain a joint dispersion curve. The joint criterion for the joint dispersion curve is as follows:
[0014]
[0015] In the above formula, f is the surface wave frequency, and c sf (f), c hwf (f) shows the dispersion curves of DAS seismic records from straight optical fibers and spirally wound optical fibers, respectively. j (f) represents the dispersion curve after the combination.
[0016] Furthermore, in step S3, the particle swarm optimization algorithm is used to invert the dispersion curve, which can avoid getting trapped in local minima during the inversion of the surface wave dispersion curve. The inversion objective function is constructed based on the Haskell-Thomson matrix method:
[0017]
[0018] In the above formula, w i These are the weighting coefficients. and f iobs where c(f) is the surface wave phase velocity versus frequency, m is the input medium model, T is the determinant of the forward dispersion curve calculation at the i-th point, T(v,f,m) = det(H(v,f,m)), where H(v,f,m) is the Haskell-Thomson matrix, and l is the norm order function.
[0019] Further, in step S3, a deterministic inversion algorithm based on the steepest descent method is adopted, and a quasi-Newton metric matrix optimization algorithm is used to stabilize the inversion of the values of the density, Poisson's ratio and the P-wave velocity, the thickness of the stratum, the S-wave velocity and the S-wave velocity of the half space, the algorithm starts from the initial model m0, and in each iteration, the model is updated according to the gradient of the mismatch function:
[0020]
[0021] In the above formula, is the alpha component of the model vector at the k-th iteration, μ k is a convergence factor that controls the step size, f αβ (m k ) is the metric matrix in the parameter space, f αβ is the dual metric matrix defined in the parameter space, that is, it satisfies where alpha and beta represent the component index of the model parameter, represents the unit matrix.
[0022] Beneficial effects: the near-surface wave exploration method of the straight optical fiber and the spiral winding optical fiber combination disclosed in the application connects the straight optical fiber and the spiral winding optical fiber in the same optical path by using the optical fiber fusion method to collect and process seismic data, carries out spatial homing on the spiral winding optical fiber DAS seismic record, makes the offset distance of the seismic record of the straight optical fiber and the spiral winding optical fiber consistent in the observation coordinate system, jointly constructs the joint dispersion curve by combining the dispersion curves of the straight optical fiber and the spiral winding optical fiber, and the joint dispersion curve has the advantages of wide frequency band and multi-mode, thereby improving the precision of the near-surface S-wave velocity structure inversion. BRIEF DESCRIPTION OF DRAWINGS
[0023] The accompanying drawings are included to provide a further understanding of the application, and constitute a part of the specification, illustrate the application together with the embodiments thereof, and are used to explain the application, and do not constitute a limitation on the application.
[0024] In the drawings:
[0025] Figure 1 is a flow chart of the near-surface wave exploration method of the straight optical fiber and the spiral winding optical fiber combination of the application;
[0026] Figure 2A schematic diagram of a straight optical fiber and a spiral winding optical fiber DAS data acquisition scheme of the present application;
[0027] Figure 3 A schematic diagram of a spiral winding optical fiber near-surface experimental observation system of the present application;
[0028] Figure 4 A single-shot seismic record of the present application;
[0029] Figure 5 A straight optical fiber and spiral winding optical fiber shot record dispersion spectrum of the present application;
[0030] Figure 6 A straight optical fiber, spiral winding optical fiber and combined straight optical fiber and spiral winding optical fiber dispersion curve of the present application;
[0031] Figure 7 A straight optical fiber, spiral winding optical fiber and combined straight optical fiber and spiral winding optical fiber shot record S-wave velocity and dispersion curve inversion result of the present application. DETAILED DESCRIPTION
[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. The following text only describes an embodiment of a straight optical fiber and spiral winding optical fiber combined near-surface wave exploration method of the present application, and does not strictly limit the protection scope of the present application.
[0033] In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the fact that a person of ordinary skill in the art can realize it. When the combination of technical solutions appears to be contradictory or unachievable, it should be considered that the combination of technical solutions does not exist and is not within the protection scope of the present application.
[0034] Embodiment one: a straight optical fiber and spiral winding optical fiber combined near-surface wave exploration method, as shown in the figure, comprising the following steps: Figure 1
[0035] S1: based on straight optical fiber and spiral winding optical fiber DAS seismic data acquisition and processing, design a straight optical fiber and spiral winding optical fiber design observation system, simultaneously carry out active source excitation, and respectively pick up straight optical fiber and spiral winding optical fiber DAS active source seismic records;
[0036] S2: based on the joint of the straight optical fiber and spiral winding optical fiber surface wave dispersion curve, the corresponding multimode surface wave dispersion curve of the straight optical fiber and spiral winding optical fiber is obtained, and the dispersion curve obtained by the straight optical fiber is combined with the dispersion curve obtained by the spiral winding optical fiber to obtain a joint dispersion curve;
[0037] S3: Based on the inversion of the joint straight fiber and spiral winding fiber surface wave dispersion curve, the inversion objective function is constructed based on the Haskell-Thomson matrix method, and the shear wave velocity is inverted by the deterministic inversion algorithm based on the steepest descent method.
[0038] In embodiment one, as shown in the figure, Figure 2 In step S1, the straight fiber and the spiral winding fiber are connected in the same optical path by fiber fusion, the spiral winding fiber collects more abundant surface wave information by changing the winding method of the fiber, the seismic record is obtained by synchronous acquisition of the joint straight fiber and spiral winding fiber, and the seismic record is preprocessed, including removing the direct current component, detrending, low-pass filtering and downsampling. The effects of low-frequency noise of the DAS instrument are suppressed by removing the direct current component and detrending, and high-frequency noise is filtered out by low-pass filtering and downsampling, while the data size is reduced and the calculation efficiency is improved.
[0039] Embodiment two: as shown in the figure, Figure 3 The straight fiber and spiral winding fiber DAS surface wave measurement is carried out in the near-surface. In order to ensure good coupling between the optical cable and the underground medium, the straight cable and the spiral winding cable are buried in the underground 15cm deep. The DAS acquisition parameters are: pitch length 2m, trace interval 0.2m, sampling frequency 1kHz, the spiral winding angle of the spiral winding cable used is α=13.8°, as shown in the figure, Figure 4 The single-shot seismic record is obtained by using a 28-pound hammer to hit the ground, wherein Figure 4 (a) is the straight fiber DAS seismic record, Figure 4 (b) is the spiral winding fiber DAS seismic record.
[0040] In embodiment two, the same line straight fiber and spiral winding fiber DAS seismic record is picked up in the seismic record, the spiral winding fiber DAS seismic record is spatially homed, and the offset distance of the straight fiber and spiral winding fiber DAS seismic record in the observation coordinate system is consistent:
[0041] x hwf =x sf ·sinα; (1)
[0042] In the above formula, x sf is the straight fiber DAS trace interval, α is the winding angle of the spiral winding fiber, and x hwf is the spiral winding fiber DAS trace interval.
[0043] In embodiment two, the seismic record is subjected to spectral analysis, as shown in the figure, Figure 5 According to the picked-up straight fiber and spiral winding fiber DAS seismic record, the phase-weighted stacking method is used to perform dispersion spectrum imaging on the sixth shot DAS seismic record, whereinFigure 5 (a) is the dispersion spectrum after acquisition and processing by a straight optical fiber. Figure 5 (b) is the dispersion spectrum after acquisition and processing by helical wound optical fiber. The dispersion spectrum after acquisition and processing by helical wound optical fiber has a wider bandwidth than that after acquisition and processing by straight optical fiber. Clear high-order mode dispersion energy can still be seen at a frequency of 130Hz.
[0044] Example 3: The dispersion curves recorded by the DAS shot gathers of straight optical fibers and helically wound optical fibers are combined to obtain a joint dispersion curve. The joint criterion for the joint dispersion curve is as follows:
[0045]
[0046] In the above formula, f is the surface wave frequency, and c sf (f), c hwf (f) shows the dispersion curves of DAS seismic records from straight optical fibers and spirally wound optical fibers, respectively. j (f) represents the dispersion curve after the combination.
[0047] In Example 3: as Figure 6 As shown, according to formula (2), the position of the fundamental order curve is confirmed by combining the dispersion spectrum of the DAS shot gather recorded by the straight fiber and the spiral wound fiber, and the combined fundamental order dispersion curve is obtained by fusing them. The dispersion spectrum of the DAS shot gather recorded by the straight fiber and the spiral wound fiber is combined to enhance the first order dispersion curve. Then, the higher order curve of the dispersion spectrum of the DAS shot gather recorded by the spiral wound fiber is picked up, and finally the combined dispersion curve is obtained. Compared with the dispersion curve of the DAS seismic record of the straight fiber and the spiral wound fiber, the combined dispersion curve contains three modes and the frequency band is broadened to 180Hz. It has the advantages of wide frequency band and multiple modes, which can improve the accuracy of near-surface shear wave velocity structure inversion.
[0048] Example 4: Using the particle swarm optimization algorithm to invert the dispersion curve can avoid getting trapped in local minima during the inversion of the surface wave dispersion curve. The inversion objective function is constructed based on the Haskell-Thomson matrix method:
[0049]
[0050] In the above formula, w i These are the weighting coefficients. and f i obs Let C(v,f,m) represent the surface wave phase velocity and frequency obtained from the dispersion curve c(f), m be the input medium model, T be the determinant of the forward modeling of the dispersion curve calculated at point i, T(v,f,m)=det(H(v,f,m)), H(v,f,m) be the Haskell-Thomson matrix, and l be the norm order function.
[0051] In embodiment four, a deterministic inversion algorithm based on the steepest descent method is adopted, and a quasi-Newton metric matrix optimization algorithm is used to stabilize the initial model m0. The density, Poisson's ratio and longitudinal wave velocity values of the initial model m0 are assumed in advance, and the thickness of the stratum, the transverse wave velocity and the transverse wave velocity of the half space are inverted. The algorithm starts from the initial model m0, and updates the model according to the gradient of the mismatch function in each iteration:
[0052]
[0053] In the above formula, is the alpha component of the model vector at the kth iteration, μ k is a convergence factor that controls the step size, f αβ (m k ) is the metric matrix in the parameter space, f αβ is the dual metric matrix defined in the parameter space, that is, it satisfies where α and β represent the component index of the model parameter, represents the unit matrix.
[0054] In embodiment four: as shown in Figure 7 , the initial model is established and the particle swarm optimization algorithm is set to invert the dispersion curve of the transverse wave velocity search range, wherein Figure 7 (a) is the transverse wave velocity profile inversion result and the corresponding dispersion curve of the straight optical fiber, Figure 7 (b) is the transverse wave velocity profile inversion result and the corresponding dispersion curve of the spiral wrapped optical fiber dispersion curve, Figure 7 (c) is the transverse wave velocity profile inversion result and the corresponding dispersion curve of the joint straight optical fiber and spiral wrapped optical fiber, from the inversion structure of the transverse wave velocity of the straight optical fiber, the spiral wrapped optical fiber and the joint straight optical fiber and the spiral wrapped optical fiber, and the inversion result of the dispersion curve, it is shown that the effective bandwidth of the straight optical fiber DAS surface wave dispersion spectrum is relatively narrow, which leads to higher uncertainty in the high frequency range (> 80Hz), while the spiral wrapped optical fiber DAS surface wave dispersion spectrum has more modal information and a wider effective frequency band, which provides more constraints for the inversion of the dispersion curve. The inversion result of the spiral wrapped optical fiber DAS dispersion curve shows that the thick layer with a depth of 7.5m-13.5m exists, and there is no obvious low-velocity layer in the shallow layer. The joint straight optical fiber and spiral wrapped optical fiber DAS observation dispersion curve, the high-order modal dispersion information of the joint dispersion curve is more abundant than that of the straight optical fiber and the spiral wrapped optical fiber, and the inversion result of the joint dispersion curve shows that the velocity structure of the layer is thicker, and the transverse wave velocity structure of the shallow layer shows an increasing trend. The near-surface wave exploration method provided by the straight optical fiber and the spiral wrapped optical fiber has the advantages of wide frequency band and multi-modal, and can obtain more reliable inversion results.
[0055] The above has described only the present application and its embodiments, which are not restrictive, and the person skilled in the art will realize that the embodiments described herein are to help the reader to understand the principles of the present application and should be understood as the protection scope of the present application not being limited to such specific statements and embodiments, and the person skilled in the art can make various other specific modifications and combinations according to the technical inspirations disclosed by the present application without departing from the essence of the present application, and these modifications and combinations still fall within the protection scope of the present application.
Claims
1. A near-Earth surface wave exploration method combining straight optical fibers and helically wound optical fibers, characterized in that, Includes the following steps: S1: Based on the acquisition and processing of DAS seismic data from straight fiber and spiral wound fiber, design observation systems for straight fiber and spiral wound fiber, and simultaneously carry out active source excitation to pick up DAS active source seismic records from straight fiber and spiral wound fiber respectively. S2: Based on the combination of the surface wave dispersion curves of straight fiber and spiral wound fiber, the multimode surface wave dispersion curves corresponding to the straight fiber and spiral wound fiber are obtained. The dispersion curve obtained from the straight fiber and the dispersion curve obtained from the spiral wound fiber are combined to obtain the joint dispersion curve. S3: Inversion of surface wave dispersion curves based on joint straight fiber and helical wound fiber, construction of inversion objective function based on Haskell-Thomson matrix method, and inversion of shear wave velocity based on deterministic inversion algorithm of steepest descent method.
2. The near-surface wave exploration method combining straight optical fiber and helical wound optical fiber according to claim 1, characterized in that: In step S1, straight optical fibers and spirally wound optical fibers are connected in series in the same optical path using optical fiber fusion splicing to synchronously acquire seismic data and obtain seismic records.
3. The near-surface wave exploration method combining straight optical fiber and helical wound optical fiber according to claim 1, characterized in that: In step S1, straight fiber and spiral-wound fiber DAS seismic records of the same survey line are picked from the seismic records. The spiral-wound fiber DAS seismic records are spatially repositioned to ensure that the offset of the straight fiber and spiral-wound fiber DAS seismic records in the observation coordinate system remains consistent. x hwf =x sf ·sinα; (1) In the above formula, x sf The straight fiber DAS channel spacing is α, where α is the winding angle of the helically wound fiber, and x is the angle of the helical winding fiber. hwf The spacing between DAS channels of helically wound optical fiber.
4. The near-surface wave exploration method combining straight optical fiber and helical wound optical fiber according to claim 1, characterized in that: In step S2, the dispersion spectra of the DAS shot gather records from straight fiber and spirally wound fiber are calculated using the phase-weighted superposition method. The dispersion curves of the DAS shot gather records from straight fiber and spirally wound fiber are then combined to obtain a joint dispersion curve. The joint criterion for the joint dispersion curve is as follows: In the above formula, f is the surface wave frequency, and c sf (f), c hwf (f) shows the dispersion curves of DAS seismic records from straight optical fibers and spirally wound optical fibers, respectively. j (f) represents the dispersion curve after the combination.
5. The near-surface wave exploration method combining straight optical fiber and helical wound optical fiber according to claim 1, characterized in that: In step S3, the particle swarm optimization algorithm is used to invert the dispersion curve to avoid getting trapped in local minima during the surface wave dispersion curve inversion. The inversion objective function is constructed based on the Haskell-Thomson matrix method: In the above formula, w i These are the weighting coefficients. and f i obs Let C(v,f,m) represent the surface wave phase velocity and frequency obtained from the dispersion curve c(f), m be the input medium model, and T be the determinant of the forward modeling of the dispersion curve calculated at point i. T(v,f,m) = det(H(v,f,m)), where H(v,f,m) is the Haskell-Thomson matrix and l is the norm order function.
6. The near-surface wave exploration method combining straight optical fiber and helical wound optical fiber according to claim 5, characterized in that: In step S3, a deterministic inversion algorithm based on the steepest descent method is adopted, and the stability of the algorithm is optimized using a quasi-Newton metric matrix. The algorithm pre-assumes the density, Poisson's ratio, and P-wave velocity values of the initial model m0, and inverts the formation thickness, S-wave velocity, and S-wave velocity in the half-space. The algorithm starts from the initial model m0 and updates the model in each iteration based on the gradient of the mismatch function. In the above formula, It is the α component of the model vector at the k-th iteration, μ k It is the convergence factor that controls the step size, f αβ (m k f is the metric matrix in the parameter space. αβ It is the dual metric matrix defined in the parameter space, that is, it satisfies Where α and β represent the component indices of the model parameters, Represents the identity matrix.