A layer stripping velocity scanning method applicable to lunar exploration radar data

Abstract

The present invention relates to a layer stripping velocity scanning method applicable to lunar radar data, including adjusting the two-way travel time of the original record to one-way travel time; manually selecting diffracted waves in the record and numbering them according to the arrival time sequence; selecting several diffracted reference points and calculating the arrival time curves of each point source; adjusting the assumed dielectric constant value of the current layer until the three characteristic points of the currently processed diffracted wave are parallel to the nearby arrival time curve; taking the assumed dielectric constant value as the true dielectric constant value of the current layer; performing time-depth conversion on the arrival time of the vertex of the currently processed diffracted wave and taking this depth as the bottom interface of the current layer; processing all diffracted waves in sequence from shallow to deep and outputting a complete dielectric constant (velocity) layered model. This method helps to accurately depict the velocity structure of lunar regolith media, and the finally constructed lunar regolith electrical property (dielectric constant) model provides prior information for subsequent research work such as further dividing and interpreting lunar horizons and inferring lunar regolith structures.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic technology, and particularly relates to a scanning method for accurately constructing a velocity (dielectric constant) structure model of lunar regolith medium. A velocity scan from shallow to deep is performed on the diffracted wave information in the lunar penetrating radar record. The velocity scan of the deep layer takes into account the velocity influence of the shallow layer. Through the conversion relationship between velocity and dielectric constant, the scanned velocity result is converted into dielectric constant, thereby effectively constructing the electrical property structure of lunar regolith. Background Art

[0002] The lunar penetrating radar (LPR) carried on the "Chang'e-3", "Chang'e-4" and "Chang'e-5" detectors successfully launched by China is a detection device installed on a lunar rover, and adopts a detection method of on-site landing observation of the lunar surface. Theoretically, a high-frequency electromagnetic pulse signal (1 MHz - 10 GHz) is transmitted to the lunar surface by a transmitting antenna. The pulse signal propagates into the lunar regolith layer and lunar crust bedrock. When the pulse signal encounters an uneven layer, such as a medium interface and an abnormal rock mass, reflected signals and diffracted signals will be transmitted back and captured by the receiving antenna. By processing, analyzing and inverting the collected data, the goal of high-resolution detection of the thickness distribution of the lunar regolith layer and revealing the subsurface geological structure under the inspection path is achieved.

[0003] Currently, in-situ detection studies on the lunar surface show that there may be uneven rock masses in the lunar regolith layer, the medium has random characteristics, and the dielectric constant of the lunar regolith also varies with depth. Therefore, it is very necessary to establish an accurate velocity model of the lunar regolith layer by developing a velocity analysis method based on lunar penetrating radar data for inferring the dielectric constant distribution of lunar regolith medium, analyzing the shallow lunar surface geological structure, and deepening the understanding of the formation and evolution of lunar regolith.

[0004] The velocity analysis method originated from the exploration seismology field. The propagation velocity parameters of seismic waves run through the whole process of seismic exploration data acquisition, processing and interpretation. From the optimization of observation system and illumination compensation based on model illumination analysis, to conventional stacking processing, post-stack (pre-stack) time (depth) migration, and then to time-depth conversion, etc. From a physical perspective, the diffracted wave field in the acquired full wave field carries high-resolution or even ultra-high-resolution underground structure information, which helps to accurately depict small-scale underground structures and rock masses. However, since the energy of diffracted waves is one to two orders of magnitude smaller than that of reflected waves, and most of the conventional seismic processing procedures and migration operators are targeted at reflected waves, the diffracted wave field is extremely vulnerable to the suppression of the reflected wave field and is thus ignored. Simply carrying out depth migration and time migration methods based on classical diffracted wave stacking can only enhance the energy of diffracted waves at each point constituting the reflection layer, but weaken the energy generated by a single diffracted point. Therefore, it is very necessary to develop a velocity analysis method based on diffracted waves for the fine characterization and interpretation of heterogeneous bodies such as buried rock blocks and fractures underground.

[0005] Regarding the velocity analysis and migration imaging of diffracted waves, scholars have carried out relevant research. Harlan first used diffracted events for migration velocity analysis and successfully separated the diffractions at fault cusps by statistical means, quantifying diffracted focusing. de Vries and Berkhout introduced the concept of minimum entropy to evaluate diffracted waves and applied this theory to migration velocity analysis. He and Yang used the parameter derived from data AGFDH to simulate the diffracted wave response to achieve velocity analysis. Sava and Biondi introduced diffracted wave imaging into the wave equation migration velocity analysis, improving the accuracy of migration imaging by correcting the time deviation of specular reflection energy, and then applied this method to seismic and ground penetrating radar data. Fomel et al. used a plane wave deconstruction filter to separate diffracted waves and reflected waves and carried out velocity analysis by means of velocity continuation method. Moser carried out research on the migration imaging of diffracted waves in the depth domain.

[0006] Since electromagnetic waves and seismic waves have high similarities in dynamic and kinematic characteristics, this provides the possibility for the velocity analysis method to extend from the seismic exploration field to the research fields of ground penetrating radar and lunar radar. However, the current research on applying the velocity analysis principle, especially the velocity analysis based on diffracted waves, to the electromagnetic exploration field is still insufficient. In particular, the research on applying the velocity analysis method based on diffracted waves to the data processing of lunar radar to obtain the velocity structure (dielectric constant structure) of lunar soil medium is also relatively limited.

[0007] Based on this, it is necessary to develop a layer stripping velocity scanning method applicable to lunar radar data to effectively solve the above problems. Summary of the Invention

[0008] The object of the present invention is to provide a layer stripping velocity scanning method applicable to lunar exploration radar data for constructing a velocity (dielectric constant) structure model of lunar regolith medium, so as to solve the problem of accurately depicting the electrical structure of lunar regolith. This method realizes velocity (dielectric constant) scanning based on each diffracted wave in the radar record in sequence from shallow to deep according to the ascending order of arrival time by identifying and picking up the diffracted wave information in the records of the Chang'e-4 lunar exploration radar. The velocity scanning of the deep layer takes into account the velocity influence of the shallow layer, which helps to accurately depict the velocity structure of lunar regolith medium. The finally constructed electrical property (dielectric constant) model of lunar regolith provides a basis and evidence for subsequent research work such as further dividing and interpreting lunar horizons, inferring the structure and evolution process of lunar regolith, etc.

[0009] The object of the present invention is realized by the following technical solutions:

[0010] First, adjust the two-way travel time of the original record of the Chang'e-4 lunar exploration radar to one-way travel time, manually select recognizable diffracted waves in the record, extract two points at the vertex and the two wings of each diffracted wave, and sort and number all the picked diffracted waves in sequence according to the ascending order of the arrival time corresponding to the vertex; second, select the diffracted wave with the smallest current number as the processing object, and given the assumed relative dielectric constant value (corresponding to an assumed velocity value) of the current layer, combine the velocity from the ground surface to the upper layer, and perform time-depth conversion on the arrival time corresponding to the vertex of the currently processed diffracted wave. The converted depth is the maximum possible depth of the diffracted point corresponding to this diffracted wave; then, select several diffracted reference points, calculate the arrival time curves of each point source wave field reaching the ground surface, and compare them with the three characteristic points of the currently processed diffracted wave. During the comparison process, continuously adjust the assumed relative dielectric constant value (assumed velocity value) of the current layer until these three points are parallel to the simulated arrival time curve in their vicinity. At this time, it is considered that the assumed relative dielectric constant value is the true relative dielectric constant value of the current layer. According to the true relative dielectric constant value of the current layer, perform time-depth conversion on the arrival time corresponding to the vertex of the currently processed diffracted wave again, and take this depth as the bottom interface of the current layer; finally, process all the diffracted waves in sequence from shallow to deep according to the above operations, and finally output a complete relative dielectric constant (velocity) layered model.

[0011] A layer stripping velocity scanning method applicable to lunar exploration radar data includes the following steps:

[0012] a. Input: Adjust the two-way travel time of the radar original record to one-way travel time;

[0013] b. Travel time adjustment: Manually select recognizable diffracted waves in the one-way travel time record after the conversion in step a;

[0014] c. Sorting and numbering: Sort and number all the picked diffracted waves in sequence according to the ascending order of the arrival time corresponding to the vertex;

[0015] d. Select the diffracted wave with the minimum vertex arrival time among all unprocessed diffracted waves as the current processing object;

[0016] e. Assignment: Given a relative dielectric constant value smaller than the minimum relative dielectric constant value of the medium in the study area as the assumed relative dielectric constant value of the current layer; Combine the velocity from the surface to the upper layer and perform time-depth conversion on the arrival time corresponding to the vertex of the diffracted wave being currently processed. The converted depth is the maximum possible depth corresponding to the target body that generates the diffracted wave; If there is no upper layer, perform time-depth conversion on the arrival time corresponding to the vertex of the current diffracted wave according to the assumed relative dielectric constant value of the current layer;

[0017] f. At equal intervals, select several points at the same horizontal position as the vertex of the diffracted wave being currently processed between this depth and the surface as the reference positions of the target body that generates the diffracted wave; Using the selected points as sources, combine the relative dielectric constant value from the surface to the upper layer and the assumed relative dielectric constant value of the current layer, and based on the fast marching method of the wavefront, calculate the arrival time curves of the wave fields generated by each point source reaching the surface;

[0018] g. Compare the arrival time curves of the wave fields generated by each point source reaching the surface in step f with the three points of the currently processed diffracted wave picked in step b; If these three points are parallel to the simulated arrival time curves in their vicinity, it can be considered that the assumed relative dielectric constant value is the true relative dielectric constant value of the current layer; If these three points are not parallel to the simulated arrival time curves in their vicinity, readjust the assumed relative dielectric constant value of the current layer, repeat step f, and then match the two again; Repeat this process until the two are parallel to obtain the true relative dielectric constant value of the current layer;

[0019] h. According to the true relative dielectric constant value of the current layer obtained in step g, perform time-depth conversion on the arrival time corresponding to the vertex of the currently processed diffracted wave again, and take this depth as the bottom interface of the current layer;

[0020] i. Repeat steps d to h until all numbered diffracted waves in step b are processed in sequence, that is, a complete layered model is obtained; For the part deeper than the bottom interface of this layered model, make its relative dielectric constant value equal to the relative dielectric constant value of the last layer;

[0021] j. Moderately smooth the layered model in step i to obtain the final relative dielectric constant model.

[0022] Further, in step b, during the picking process, first extract the recording segment where the diffracted wave is located, and then pick the vertex of the diffracted wave and two points at the positions of its two wings.

[0023] Further, in step d, the diffracted wave with the minimum vertex arrival time is the diffracted wave with the smallest number.

[0024] Further, step e corresponds to a velocity value that is greater than the maximum velocity value of the medium within the study area; the velocity value is obtained according to the conversion formula between relative permittivity and velocity: In the formula, v represents the propagation velocity of electromagnetic waves in the formation, and ε r represents the relative permittivity value, and c = 3×10 8 m / s represents the speed of light.

[0025] Furthermore, step g involves three points, namely the vertex and two points at the wing positions.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] The present invention proposes a velocity scanning method based on diffracted waves and applies it to the processing of lunar radar data for constructing the velocity (permittivity) structure of lunar regolith media; by identifying and picking up the diffracted wave information in the lunar radar records, and in the order of increasing arrival time, the velocity (permittivity) scanning based on each diffracted wave in the radar records is sequentially realized from shallow to deep, and the velocity scanning of the deep layer takes into account the influence of the shallow layer velocity, which helps to accurately construct the velocity (permittivity) structure model of the lunar regolith media along the path of the rover. Specifically, the following advantages are achieved:

[0028] 1. By using velocity analysis based on diffracted waves instead of reflected waves, the diffracted wave field carries high-resolution or even ultra-high-resolution underground structure information, which helps to accurately depict small-scale underground structures and rock masses.

[0029] 2. It is applicable to the self-excitation and self-reception acquisition mode, that is, velocity scanning is realized for the data collected by the lunar radar carried on the Chang'e series of detectors launched by China.

[0030] 3. By adopting the method of layer-by-layer velocity scanning from shallow to deep, and considering the influence of the shallow layer velocity when scanning the deep layer velocity, the accuracy and reliability are effectively improved.

[0031] 4. The stratification information of the lunar regolith media is quantified, and a more accurate stratification basis is provided by the permittivity layer model, which provides evidence for the layer division relying solely on the reflection wave interface.

[0032] 5. After velocity scanning, a permittivity layer model of the lunar regolith media can be obtained, which helps to deeply understand the lunar regolith geological information and provides prior information for subsequent research work such as further dividing and interpreting the lunar horizons, inferring the lunar regolith structure and evolution process, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the attached drawings required for the embodiments. It should be understood that the following attached drawings only show some embodiments of the present invention, and therefore should not be regarded as a limitation of the scope. For those of ordinary skill in the art, without creative efforts, other relevant attached drawings can also be obtained based on these attached drawings.

[0034] Figure 1 Flowchart of the layer stripping velocity scanning method applicable to lunar exploration radar data;

[0035] Figure 2 Example 1: Rock fragment model of lunar regolith layer;

[0036] Figure 3 Example 1: Original simulated radar record;

[0037] Figure 4 Example 1: Diffraction waves picked up from the original simulated radar record;

[0038] Figure 5 Example 1: Diffraction wave with the minimum vertex arrival time (number ①);

[0039] Figure 6 Example 1: Diffraction wave with the minimum vertex arrival time (selecting several point sources);

[0040] Figure 7 Example 1: Comparison result of the simulated arrival time curve and the characteristic points of the diffraction wave (ε r = 2);

[0041] Figure 8 Example 1: Comparison result of the simulated arrival time curve and the characteristic points of the diffraction wave (ε r = 3);

[0042] Figure 9 Example 2: Original record of the Chang'e-4 lunar exploration radar;

[0043] Figure 10 Example 2: Diffraction wave with the minimum vertex arrival time and three selected characteristic points;

[0044] Figure 11 Example 2: Diffraction waves picked up from the original simulated radar record (with numbers);

[0045] Figure 12 Example 2: Diffraction wave with the minimum vertex arrival time (selecting several point sources);

[0046] Figure 13 Example 2: Comparison result of the simulated arrival time curve and the characteristic points of the diffraction wave (ε r = 3.5);

[0047] Figure 14 Example 2: Comparison results of the simulated arrival time curve and the diffraction wave characteristic points (ε r = 3.8);

[0048] Figure 15 Example 2: Velocity scanning results of the Chang'e-4 lunar radar data;

[0049] Figure 16 Example 2: Smoothing results of the velocity scanning of the Chang'e-4 lunar radar data. Specific implementation manners

[0050] The present invention will be further described below in conjunction with the embodiments:

[0051] The present invention will be further described in detail below in conjunction with the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. In addition, it should be noted that, for the sake of description, only the parts related to the present invention rather than all the structures are shown in the drawings.

[0052] It should be noted that: Similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used for distinguishing descriptions, and cannot be understood as indicating or implying relative importance.

[0053] Example 1

[0054] a. Input the original radar record and adjust the two-way travel time of the original record to the one-way travel time. A lunar soil layer rock fragment model containing a disturbance body is used, such as Figure 2 shown, to synthesize the original simulated radar record. The size of this layered model is 49.9m * 14.9m, and there is an air layer with h a = 1m at the top of the model; the finite difference grid spacing h = 10cm, so this model has a total of N M = 160 × 500 = 80000 grid points. The model contains a total of three layers of media, and the thickness and relative dielectric constant values of each layer of media are respectively: the first layer (0m - 4.8m), the relative dielectric constant is 3; the second layer (4.9m - 9.8m), the relative dielectric constant is 5; the third layer (9.9m - 14.9m), the relative dielectric constant is 9. Five cross-shaped disturbance bodies are scattered sporadically in different layers of the model (such as Figure 2The positions circled by white circles (relative dielectric constant is 30) are located at (23.6 m, 4.4 m), (32.8 m, 6.4 m), (19.2 m, 9.4 m), (42.4 m, 10.7 m), and (10.8 m, 13.1 m) respectively. The lateral and longitudinal lengths of the disturbance bodies are both 2 grid spacings. The ground observation system adopts the self-exciting and self-receiving acquisition method, consisting of 497 transmitting antennas with a spacing of 1 grid point and 497 receiving antennas with a spacing of 1 grid point. Moreover, the signals transmitted by each antenna can be recorded by the receiving antennas 3 grid points apart; a Gaussian wavelet with a center frequency of 150 MHz is used as the wavelet for the synthetic record, that is, the wavelet is considered known.

[0055] The total recording duration of the original simulated radar record is 300 ns. After adjusting the two-way travel time of the original record to one-way travel time, the total recording duration is reduced to 150 ns, as Figure 3 shown.

[0056] b. Manually select the recognizable diffracted waves in the one-way travel time record after conversion in step a. Since the sizes of the scattered blocks in the layered model are slightly smaller than or approximately equal to the wavelength of the electromagnetic wave, the diffracted waves in the radar profile correspond to the interfaces with larger bending amplitudes (larger curvatures). Figure 4 The white curves in Figure 5 represent 5 recognizable diffracted waves manually selected from the original radar record generated by simulation. They are respectively generated by 5 disturbance bodies scattered in the layered model. Taking the diffracted wave with the smallest vertex arrival time as an example, during the selection process, first extract the recording segment where the diffracted wave is located, and then pick two points at the vertex and the two wings positions of the diffracted wave, as

[0057] shown. Figure 4 shown.

[0058] d. Among all the unprocessed diffracted waves, select the diffracted wave with the smallest vertex arrival time (the smallest current serial number) as the current processing object, as Figure 5 shown, denoted as D i (i = 1, 2, 3, 4, 5, and i is consistent with the serial number of the currently processed diffracted wave).

[0059] e. Given a relative dielectric constant value smaller than the minimum relative dielectric constant value of the medium in the study area as the assumed ε r i value of the current layer.

[0060] Taking the diffracted wave with the smallest vertex arrival time (serial number ○1) as an example, as Figure 5As shown, first, the minimum relative permittivity value of the medium within the study area A relative permittivity value smaller than this value is given as the assumed ε value for the current layer r i value, and the given value ε r i = 2;

[0061] The conversion formula between velocity and relative permittivity:

[0062]

[0063] In the formula, c represents the propagation velocity of electromagnetic waves in vacuum, c = 3×10 8 m / s, ε r represents the relative permittivity of the medium, and v represents the propagation velocity of electromagnetic waves in the medium.

[0064] From the above conversion relationship, it can be seen that the given relative permittivity value ε r i corresponds to a velocity value v that is even greater than the maximum velocity value of the medium within the study area Combined with the velocity from the surface to the upper layer, perform time-depth conversion on the arrival time corresponding to the diffraction wave vertex being processed currently. The converted depth is the maximum possible depth corresponding to the target body that generates this diffraction wave. If there is no upper layer, perform time-depth conversion according to the assumed ε i value of the current layer r i value.

[0065] f. Between this depth and the surface, at the same horizontal position as the diffraction wave vertex being processed currently, select several points at equal intervals as the reference positions of the target body that generates this diffraction wave. For example: The diffraction wave being processed currently is the diffraction wave with the minimum arrival time at the vertex (numbered ①). At the same horizontal position as its vertex, select several points at equal intervals, as Figure 6 shown; Using the selected several points as sources, combined with the relative permittivity value ε r i-1 value from the surface to the upper layer and the assumed ε r i value of the current layer, based on the fast marching method of wavefront, calculate the arrival time curves of the wave fields generated by each point source reaching the surface, as Figure 7 shown. Figure 7 The black dashed lines in it represent the arrival time curves of the wave fields generated by each point source reaching the surface.

[0066] g. Compare with the three points (the vertex and two points at the wing positions) of the diffraction wave being processed currently picked in step b; If these three points are parallel to the simulated arrival time curves in their vicinity, it can be considered that the assumed ε r iThe value is the true value of the current layer ; if these three points are not parallel to the simulated arrival time curve in their vicinity, then adjust the assumed ε of the current layer r i value, and after repeating step f, match the two again, and repeat this process until they are parallel. At this time, the ε r i value is the true value of the current layer value;

[0067] Here, still taking the diffracted wave with the minimum arrival time at the vertex (numbered ①) as an example, when the assumed relative dielectric constant ε r i = 2, at this time, extract the three points (the vertex and the two points at the wing positions) of the diffracted wave numbered ① and compare them with the simulated arrival time curve in their vicinity. As Figure 7 shown, it is found that these three points intersect with the simulated arrival time curve in their vicinity and are not parallel, then adjust the assumed ε of the current layer r i value, adjust its value from 2 to 3, and calculate the arrival time curve of the wave field generated by each point source reaching the surface again and compare them. As Figure 8 shown, it is found that these three points are parallel to the simulated arrival time curve in their vicinity. At this time, it can be considered that the assumed relative dielectric constant value ε r i = 3 is the true value of the current layer value.

[0068] h. According to the true value of the current layer obtained in step g value, perform time-depth conversion on the arrival time corresponding to the vertex of the diffracted wave currently being processed again, and use this depth as the bottom interface of the current layer. The current layer is denoted as L i (Theoretically, the number of layers should be the same as the number of diffracted waves picked up);

[0069] i. Repeat steps d to h until the 5 diffracted waves picked up in step b are processed in sequence, and a complete layered model can be obtained; for the part deeper than the bottom interface of this layered model, make its relative dielectric constant value equal to the true relative dielectric constant value of the last layer.

[0070] j. Moderately smooth the layered dielectric constant model obtained in step i to obtain the final relative dielectric constant model.

[0071] Example 2

[0072] a. Input the original record of the Chang'e-4 lunar exploration radar, and adjust the two-way travel time of the original record to one-way travel time, that is, convert the entire time axis of the original record to half of the original value. The two-way travel time of the original lunar exploration radar record is 1000 ns, and the converted one-way travel time is 500 ns. AsFigure 9 As shown. The purpose of this operation is to eliminate the influence caused by the diffraction wave curvature on the rock blocks in the lunar regolith layer during the self-excitation and self-reception two-way travel.

[0073] b. Manually select the recognizable diffraction waves in the one-way travel record after the conversion in step a. Since the sizes of the rock debris or blocks distributed in the lunar regolith layer are slightly smaller than or approximately equal to the wavelength of the electromagnetic wave, the diffraction waves in the radar profile correspond to the interfaces with larger bending amplitudes (smaller curvatures). Figure 9 The white curves in represent 31 recognizable diffraction waves manually selected from the records of the Chang'e-4 lunar radar. During the selection process, first, the record segments where the diffraction waves are located are extracted, and then two points at the vertex and the two wings of the diffraction wave are picked up (as shown in Figure 10 ).

[0074] c. Sort all the diffraction waves picked up in step b in ascending order according to the time corresponding to the vertex, and number them as ①, ②, ③... As shown in Figure 11 .

[0075] d. Among all the unprocessed diffraction waves, select the diffraction wave with the smallest vertex arrival time (the smallest current serial number) as the current processing object, denoted as D i (i = 1, 2,..., 31, i is consistent with the serial number of the currently processed diffraction wave);

[0076] e. Given a relative dielectric constant value smaller than the minimum relative dielectric constant value of the medium in the study area as the assumed ε value of the current layer r i i .

[0077] The conversion formula between velocity and relative dielectric constant:

[0078]

[0079] In the formula, c represents the propagation speed of the electromagnetic wave in vacuum, c = 3×10 8 m / s, ε r represents the relative dielectric constant of the medium, and v represents the propagation speed of the electromagnetic wave in the medium.

[0080] From the above conversion relationship, it can be seen that the given relative dielectric constant value ε r i corresponds to a speed value v larger than the maximum speed value of the medium in the study area i ​. Combining the velocity from the surface to the upper layer, perform time-depth conversion on the arrival time corresponding to the diffracted wave vertex being currently processed. The converted depth is the maximum possible depth corresponding to the target body that generates this diffracted wave. If there is no upper layer, perform time-depth conversion according to the assumed ε value of the current layer r i value;

[0081] f. Between this depth and the surface, at the same horizontal position as the diffracted wave vertex being currently processed, select several points at equal intervals as the reference positions of the target body that generates this diffracted wave. Taking the diffracted wave with the minimum arrival time at the vertex (numbered ①) as an example, at the same horizontal position as its vertex, select several points at equal intervals, as Figure 12 shown; Using the selected several points as sources, combining the relative permittivity value ε from the surface to the upper layer r i-1 value and the assumed ε value of the current layer r i value, based on the fast marching method of the wavefront, calculate the arrival time curves of the wave fields generated by each point source reaching the surface, as Figure 13 shown. Figure 13 The black dashed lines in

[0082] represent the arrival time curves of the wave fields generated by each point source reaching the surface. r i g. Compare with the three points (the vertex and the two points at the wing positions) of the diffracted wave being currently processed picked in step b; If these three points are parallel to the simulated arrival time curves near them, it can be considered that the assumed ε value is the true r i value of the current layer; If these three points are not parallel to the simulated arrival time curves near them, adjust the assumed ε value of the current layer r i value, and repeat step f and then match the two again. Repeat this process until the two are parallel. At this time, the ε value is the true

[0083] value of the current layer; r i Here, still taking the diffracted wave with the minimum arrival time at the vertex (numbered ①) as an example, when the assumed relative permittivity ε Figure 13 is 3.5, at this time, extract the three points (the vertex and the two points at the wing positions) of the diffracted wave numbered ① and compare them with the simulated arrival time curves near them, as r i shown. It is found that these three points intersect with the simulated arrival time curves near them and are not parallel. Then adjust the assumed ε Figure 14As shown, it is found that these three points are parallel to the simulated arrival-time curves in their vicinity. At this time, it can be considered that the assumed relative dielectric constant value ε r i = 3.8 is the true value of the current layer.

[0084] h. According to the true value of the current layer obtained in step g, perform time-depth conversion on the arrival time corresponding to the vertex of the diffracted wave being processed again, and use this depth as the bottom interface of the current layer. The current layer is denoted as L i (Theoretically, the number of layers should be the same as the number of picked diffracted waves);

[0085] i. Repeat steps d to h until the 31 picked diffracted waves in step b are processed in sequence, that is, a complete layered model is obtained; for the part deeper than the bottom interface of this layered model, make its relative dielectric constant value equal to the true relative dielectric constant value of the last layer, as Figure 15 shown;

[0086] j. Moderately smooth the layered dielectric constant model obtained in step i to obtain the final relative dielectric constant ε r model, as Figure 16 shown.

[0087] Note that the above is only a preferred embodiment of the present invention and the technical principles applied. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described here. Various obvious changes, re-adjustments, and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, it can also include more other equivalent embodiments, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A layer stripping velocity scanning method applicable to lunar exploration radar data, characterized in that, It includes the following steps: a. Adjust the two-way travel time of the radar raw record to the one-way travel time; b. Manually pick out the recognizable diffracted waves from the one-way travel time record after the conversion in step a; c. Sort and number all the picked diffracted waves in ascending order according to the vertex corresponding time; d. Select the diffracted wave with the smallest vertex corresponding time among all the unprocessed diffracted waves as the current processing object; e. Given a relative dielectric constant value smaller than the minimum relative dielectric constant value of the medium in the study area as the assumed relative dielectric constant value of the current layer; combine the velocity from the surface to the upper layer, and perform time-depth conversion on the corresponding time of the vertex of the currently processed diffracted wave. The converted depth is the maximum possible depth corresponding to the target body generating this diffracted wave; if there is no upper layer, perform time-depth conversion according to the assumed relative dielectric constant value of the current layer; f. At equal intervals, select several points at the same horizontal position as the vertex of the currently processed diffracted wave between this depth and the surface as the reference positions of the target body generating this diffracted wave; take the selected points as the sources, and based on the fast marching method of the wavefront, calculate the arrival time curves of the wave fields generated by each point source reaching the surface by combining the relative dielectric constant value from the surface to the upper layer and the assumed relative dielectric constant value of the current layer; g. Compare the arrival time curves of the wave fields generated by each point source reaching the surface in step f with the three points of the currently processed diffracted wave picked in step b; if these three points are parallel to the simulated arrival time curves in their vicinity, it can be considered that the assumed relative dielectric constant value is the true relative dielectric constant value of the current layer; if these three points are not parallel to the simulated arrival time curves in their vicinity, readjust the assumed relative dielectric constant value of the current layer, repeat step f, and then match the two again; repeat this process until the two are parallel to obtain the true relative dielectric constant value of the current layer; h. According to the true relative dielectric constant value of the current layer obtained in step g, perform time-depth conversion on the corresponding time of the vertex of the currently processed diffracted wave again, and take this depth as the bottom interface of the current layer; i. Repeat steps d to h until all the numbered diffracted waves in step b are processed in sequence, that is, a complete layered model is obtained; for the part deeper than the bottom interface of this layered model, make its relative dielectric constant value equal to the relative dielectric constant value of the last layer; j. Moderately smooth the layered model in step i to obtain the final relative dielectric constant model.

2. The layer stripping velocity scanning method applicable to lunar exploration radar data according to claim 1, characterized in that: In step b, during the picking process, first extract the record segment where the diffracted wave is located, and then pick the vertex of the diffracted wave and two points at the positions of its two wings.

3. A layer stripping velocity scanning method applicable to lunar exploration radar data according to claim 1, characterized in that: In step d, the diffracted wave with the smallest vertex corresponding time is the diffracted wave with the smallest number.

4. A layer stripping velocity scanning method applicable to lunar exploration radar data according to claim 1, characterized in that: Step e corresponds to a velocity value that is even greater than the maximum velocity value of the medium within the study area; the velocity value is obtained according to the conversion formula between relative permittivity and velocity: In the formula, v represents the propagation velocity of electromagnetic waves in the formation, r represents the relative permittivity value, c = 3×10 8 m / s represents the speed of light.

5. A layer stripping velocity scanning method applicable to lunar exploration radar data according to claim 1, characterized in that: In step g, the three points are the vertex and two points at the positions of its two wings.

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