Layer stripping speed scanning method suitable for lunar exploration radar data

Abstract

The invention relates to a layer stripping speed scanning method suitable for lunar radar data. The layer stripping speed scanning method comprises the following steps: adjusting two-way travel time recorded originally into one-way travel time; diffracted waves are manually selected in the record and numbered according to the arrival time sequence; selecting a plurality of diffraction reference points, and calculating an arrival time curve of each point source; adjusting the assumed dielectric constant value of the current layer until the three feature points of the currently processed diffracted wave are parallel to the nearby arrival time curve; taking the assumed dielectric constant value as a real dielectric constant value of the current layer; performing time-depth conversion on the arrival time of the peak of the currently processed diffracted wave, and taking the depth as the bottom interface of the current layer; and all diffracted waves are sequentially processed from shallow to deep, and a complete dielectric constant (velocity) layered model is output. According to the method, the velocity structure of the lunar soil medium can be accurately described, and the finally constructed lunar soil electrical property (dielectric constant) model provides prior information for subsequent research work such as further dividing and explaining the lunar horizon and deducing the lunar soil structure.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic technology, and specifically relates to a scanning method for accurately constructing a velocity (dielectric constant) structure model of lunar soil medium. A velocity scan from shallow to deep is performed for the diffraction wave information recorded by the lunar exploration radar. 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 velocity result after scanning is converted into dielectric constant, thereby realizing the effective construction of the electrical structure of the lunar soil. Background Art

[0002] The lunar probe radar (LPR) carried by my country's Chang'e 3, Chang'e 4 and Chang'e 5 probes is a detection device mounted on the lunar rover, which uses a detection method of on-site landing observation of the lunar surface. In theory, a high-frequency electromagnetic pulse signal (1MHz~10GHz) is transmitted to the lunar surface using a transmitting antenna. The pulse signal propagates to the lunar soil layer and the bedrock of the lunar crust. When the pulse signal encounters an uneven layer, such as a medium interface and abnormal rock blocks, there will be reflected and diffracted signals 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 soil layer and revealing the geological structure of the lunar subsurface under the patrol path can be achieved.

[0003] At present, in-situ exploration studies on the lunar surface have shown that there may be uneven rock blocks in the lunar soil layer, the medium has random characteristics, and the dielectric constant of the lunar soil also changes with depth. Therefore, it is very necessary to establish an accurate lunar soil layer velocity model by conducting velocity analysis methods based on lunar radar data, in order to infer the distribution of the dielectric constant of the lunar soil medium, analyze the geological structure of the shallow lunar surface, and deepen the understanding of the formation and evolution of the lunar soil.

[0004] Velocity analysis methods originated in the field of exploration seismic. The propagation velocity parameters of seismic waves run through the entire process of seismic exploration data acquisition, processing and interpretation. From observation system optimization and illumination compensation based on model illumination analysis, to conventional stacking processing, post-stack (pre-stack) time (depth) migration, to time-depth conversion, etc. From a physical point of view, the diffraction wave field in the acquired full wave field carries high-resolution or even ultra-high-resolution underground structural information, which helps to accurately characterize underground small-scale structures and rock blocks. However, since the energy of diffraction waves is one to two orders of magnitude smaller than that of reflection waves, and conventional seismic processing procedures and migration operators are mostly aimed at reflection waves, the diffraction wave field is easily suppressed by the reflection wave field and ignored. Simply carrying out depth migration and time migration methods based on classical diffraction stacking can only enhance the diffraction wave energy of each point that constitutes the reflection layer, but weaken the energy generated by a single diffraction point. Therefore, it is very necessary to carry out velocity analysis methods based on diffraction waves for the fine characterization and interpretation of underground buried rock blocks, fractures and other heterogeneous bodies.

[0005] Scholars have conducted relevant research on velocity analysis and migration imaging of diffraction waves. Harlan first used diffraction events to perform migration velocity analysis, and successfully separated fault cusp diffraction using statistical methods and quantified diffraction focusing. de Vries and Berkhout introduced the concept of minimum entropy to evaluate diffraction waves and applied this theory to migration velocity analysis. and Yang used the data AGFDH to derive parameters to simulate the diffraction wave response to achieve velocity analysis. Sava and Biondi introduced diffraction wave imaging into wave equation migration velocity analysis, and improved the accuracy of migration imaging by correcting the time deviation of mirror reflection energy, and then applied this method to seismic and ground penetrating radar data. Fomel et al. used plane wave deconstruction filters to separate diffraction waves and reflection waves, and carried out velocity analysis with the help of velocity continuation methods. Moser conducted a study on migration imaging of diffraction waves in the depth domain.

[0006] Since electromagnetic waves and seismic waves have high similarities in dynamic and kinematic characteristics, it is possible for velocity analysis methods to be extended from the field of seismic exploration to the field of ground and lunar radar research. However, the current research on the application of velocity analysis principles, especially velocity analysis based on diffraction waves, to the field of electromagnetic exploration is still insufficient. In particular, the research on applying the velocity analysis method based on diffraction waves to the data processing of lunar radar to obtain the velocity structure (dielectric constant structure) of the lunar soil medium is also relatively limited.

[0007] Based on this, it is necessary to develop a layer peeling velocity scanning method suitable for lunar exploration radar data to effectively solve the above problems. Summary of the invention

[0008] The purpose of the present invention is to provide a layer peeling velocity scanning method suitable for lunar exploration radar data, which is used to construct a velocity (dielectric constant) structure model of the lunar soil medium to solve the problem of truly describing the electrical structure of the lunar soil. This method recognizes and picks up the diffraction wave information in the Chang'e-4 lunar exploration radar record, and sequentially realizes the velocity (dielectric constant) scanning based on each diffraction wave in the radar record in order from small to large, from shallow to deep. The velocity scanning of the deep layer takes into account the velocity influence of the shallow layer, which helps to accurately describe the velocity structure of the lunar soil medium. The lunar soil electrical (dielectric constant) model finally constructed provides a basis and evidence for the subsequent research work such as further division and interpretation of lunar strata, inference of lunar soil structure and evolution process, etc.

[0009] The objective of the present invention is achieved through the following technical solutions:

[0010] Firstly, the two-way travel time originally recorded by the Chang'e-4 lunar exploration radar is adjusted to a one-way travel time, and the identifiable diffraction waves are manually selected in the record, and the two points of the vertex and the two wings of each diffraction wave are extracted. All the picked diffraction waves are sorted and numbered in order from small to large according to the vertex corresponding to the arrival time; secondly, the diffraction wave with the smallest current number is selected as the processing object, and the assumed relative dielectric constant value of the current layer (corresponding to an assumed velocity value) is given. Combined with the velocity from the surface to the previous layer, the arrival time corresponding to the vertex of the currently processed diffraction wave is converted into time-to-depth, and the depth obtained by conversion is the maximum possible depth of the diffraction point corresponding to the diffraction wave; then, several diffraction parameters are selected to obtain the maximum possible depth of the diffraction point corresponding to the diffraction wave. Test point, calculate the arrival time curve of each point source wave field reaching the surface, and compare it with the three characteristic points of the diffraction wave currently being processed. 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 curves near them. 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, the arrival time corresponding to the vertex of the diffraction wave currently being processed is converted to time-to-depth again, and the depth is used as the bottom interface of the current layer; finally, all diffraction waves are processed in sequence from shallow to deep according to the above operations, and finally a complete relative dielectric constant (velocity) layered model is output.

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

[0012] a. Input: Adjust the two-way travel time originally recorded by the radar to the one-way travel time;

[0013] b. Adjusting the travel time: manually selecting identifiable diffraction waves from the one-way travel time record converted in step a;

[0014] c. Sorting and numbering: sorting and numbering all the picked diffraction waves in ascending order according to the corresponding vertices;

[0015] d. Select the diffraction wave with the smallest vertex arrival time from all the unprocessed diffraction waves as the current processing object;

[0016] e. Assignment: a relative permittivity value smaller than the minimum relative permittivity value of the medium in the study area is given as the assumed relative permittivity value of the current layer; combined with the velocity from the surface to the previous layer, the time-depth conversion is performed on the arrival time corresponding to the vertex of the diffraction wave currently being processed, and the depth obtained by the conversion is the maximum possible depth corresponding to the target body that generates the diffraction wave; if there is no previous layer, the time-depth conversion is performed on the arrival time corresponding to the current diffraction wave vertex according to the assumed relative permittivity value of the current layer;

[0017] f. Between the depth and the surface, at the same horizontal position as the vertex of the diffraction wave currently being processed, select several points at equal intervals as the reference positions of the target body that generates the diffraction wave; using the selected points as sources, combining the relative dielectric constant value from the surface to the previous layer and the assumed relative dielectric constant value of the current layer, based on the wavefront rapid advancement method, calculate the arrival time curve of the wave field generated by each point source to the surface;

[0018] g. Compare the arrival time curves of the wave fields generated by each point source in step f and the three points of the diffraction waves currently being processed picked up in step b; if the three points are parallel to the simulated arrival time curves near them, it can be considered that the assumed relative permittivity value is the true relative permittivity value of the current layer; if the three points are not parallel to the simulated arrival time curves near them, readjust the assumed relative permittivity value of the current layer, and repeat step f to match the two again; repeat this process until the two are parallel, and obtain the true relative permittivity value of the current layer;

[0019] h. According to the real relative dielectric constant value of the current layer obtained in step g, the time-depth conversion is performed again on the arrival time corresponding to the vertex of the diffraction wave currently being processed, and the depth is taken as the bottom interface of the current layer;

[0020] i. Repeat steps d to h until all the numbered diffraction waves in step b are processed in sequence, i.e., a complete layered model is obtained; the relative dielectric constant value of the portion deeper than the bottom interface of the layered model is set equal to the relative dielectric constant value of the last layer;

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

[0022] Furthermore, in step b, during the selection process, the recording segment where the diffraction wave is located is firstly extracted, and then the two points of the vertex and the two wings of the diffraction wave are picked up.

[0023] Further, in step d, the smallest diffraction wave at the vertex is the diffraction wave with the smallest number.

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

[0025] Furthermore, in step g, the three points are the vertex and two points at the two wings.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention proposes a velocity scanning method based on diffraction waves and applies it to lunar exploration radar data processing to construct the velocity (dielectric constant) structure of lunar soil medium; by identifying and picking up the diffraction wave information in the lunar exploration radar record, the velocity (dielectric constant) scanning based on each diffraction wave in the radar record is sequentially realized from shallow to deep in the order from small to large at the time, and the velocity scanning of the deep layer takes into account the velocity influence of the shallow layer, which is helpful to accurately construct the velocity (dielectric constant) structure model of the lunar soil medium along the rover path, and has the following advantages:

[0028] 1. Velocity analysis based on diffraction waves is used instead of velocity analysis based on reflection waves. The diffraction wave field carries high-resolution or even ultra-high-resolution underground structural information, which helps to accurately characterize underground small-scale structures and rock blocks;

[0029] 2. Applicable to the self-excited and self-collected acquisition mode, that is, to achieve speed scanning for the data collected by the lunar exploration radar carried by the Chang'e series probes launched by my country;

[0030] 3. The method of layer-by-layer velocity scanning from shallow to deep is adopted. When scanning the deep layer velocity, the influence of the shallow layer velocity is taken into consideration, which effectively improves the accuracy and reliability;

[0031] 4. The lunar soil medium stratification information was quantified, and the dielectric constant layered model provided a more accurate stratification basis, providing evidence for the stratification based solely on the reflection wave interface;

[0032] 5. After velocity scanning, the dielectric constant layered model of the lunar soil medium can be obtained, which helps to gain a deeper understanding of lunar soil geological information and provide prior information for subsequent research work such as further division and interpretation of lunar strata, inference of lunar soil structure and evolution process, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 Flow chart of layer stripping velocity scanning method applicable to lunar radar data;

[0035] Figure 2 Example 1: Lunar soil rock fragment model;

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

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

[0038] Figure 5 Embodiment 1: The smallest diffraction wave at the vertex (number ①);

[0039] Figure 6 Example 1: The smallest diffraction wave at the vertex (selecting several point sources);

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

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

[0042] Fig. 9 Example 2: Chang'e-4 lunar exploration radar original record;

[0043] Fig.10 Embodiment 2: The smallest diffraction wave at the vertex and the three selected characteristic points;

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

[0045] Fig.12 Example 2: The smallest diffraction wave at the vertex (selecting several point sources);

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

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

[0048] Fig.15 Example 2: Chang'e 4 lunar exploration radar data velocity scan results;

[0049] Fig.16 Example 2: Chang'e-4 lunar exploration radar data velocity scanning smoothing results. DETAILED DESCRIPTION

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

[0051] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

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

[0053] Example 1

[0054] a. Input the original radar record and adjust the round trip travel time of the original record to the one-way travel time. Use the lunar soil layer rock fragment model including the disturbance body, such as Figure 2 As shown, the original simulated radar record is synthesized. The size of the layered model is 49.9m*14.9m, and there is h on the top of the model. a = 1m of air layer; finite difference grid spacing h = 10cm, so the model has a total of N M =160×500=80000 grid points. The model contains three layers of dielectrics, and the thickness and relative dielectric constant of each layer are as follows: 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 in different layers of the model (such as Figure 2The white circle indicates the position), the relative dielectric constant is 30, and they are located at (23.6m, 4.4m), (32.8m, 6.4m), (19.2m, 9.4m), (42.4m, 10.7m) and (10.8m, 13.1m), respectively. The horizontal and vertical lengths of the disturbance body are both 2 grid spacings. The ground observation system adopts a self-excited 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. The signal transmitted by each antenna can be recorded by the receiving antenna 3 grid points apart; the Gaussian wavelet with a center frequency of 150MHz is used as the wavelet of the synthetic record, that is, the wavelet is considered to be known.

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

[0056] b. Manually select the identifiable diffraction waves in the one-way travel time record converted in step a. Since the size of the scattered blocks in the layered model is slightly smaller than or similar to the wavelength of the electromagnetic wave, the diffraction waves in the radar profile correspond to the interface with a larger bending amplitude (larger curvature). Figure 4 The white curve in the middle represents the five identifiable diffraction waves manually selected from the original radar records generated by the simulation. They are generated by five disturbance bodies scattered in the layered model. Taking the diffraction wave with the smallest vertex arrival time as an example, in the selection process, the record segment where the diffraction wave is located is first extracted, and then the two points of the vertex and the two wings of the diffraction wave are picked up, such as Figure 5 shown.

[0057] c. Sort the five diffraction waves picked up in step b in ascending order according to the time when the vertices correspond to them, and number them as ①, ②, ③, ④, ⑤, such as Figure 4 shown.

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

[0059] e. Give a minimum relative permittivity value for the medium in the study area. A smaller relative permittivity value is also required as the assumed ε of the current layer r i value.

[0060] Take the diffraction wave with the smallest vertex (numbered ○1) as an example, Figure 5As shown, first, the minimum relative permittivity value of the medium in the study area is Given a smaller relative permittivity value than this value as the assumed ε for the current layer r i Value, given value ε r i =2;

[0061] Conversion formula between velocity and relative dielectric constant:

[0062]

[0063] In the formula, c represents the propagation speed of electromagnetic waves 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 electromagnetic waves in the medium.

[0064] From the above conversion relationship, we can know that the given relative dielectric constant value ε r i Corresponding to a value greater than the maximum velocity of the medium in the study area A larger speed value v is required i Combined with the velocity from the surface to the previous layer, the time-depth conversion is performed on the arrival time corresponding to the vertex of the diffraction wave currently being processed. The depth obtained by the conversion is the maximum possible depth of the target body that generates the diffraction wave. If there is no previous layer, ε is assumed according to the current layer. r i The value is converted to time depth.

[0065] f. Between the depth and the surface, at the same horizontal position as the vertex of the diffraction wave currently being processed, select several points at equal intervals as the reference position of the target body that generates the diffraction wave. For example: the diffraction wave currently being processed is the diffraction wave with the smallest vertex (numbered ①). At the same horizontal position of its vertex, select several points at equal intervals, such as Figure 6 As shown; taking several selected points as sources, combined with the relative dielectric constant value ε from the surface to the upper layer r i-1 value and the assumed ε of the current layer r i Based on the wavefront rapid advancement method, the arrival time curve of the wave field generated by each point source reaching the surface is calculated, such as Figure 7 shown. Figure 7 The black dashed lines in the middle represent the arrival time curves of the wave fields generated by each point source reaching the surface.

[0066] g. Compare the three points of the diffraction wave currently processed (the vertex and the two points on the two wings) picked up 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 r iThe value is the real value of the current layer. If these three points are not parallel to the simulated arrival time curves near them, adjust the assumed ε of the current layer r i value, and repeat step f to match the two again, and repeat this process until the two are parallel. At this time, ε r i The value is the real value of the current layer. value;

[0067] Here we still take the diffraction wave with the smallest peak (numbered ①) as an example. When the relative dielectric constant ε is assumed r i = 2, the three points extracted from the diffraction wave numbered ① (the vertex and the two points on the two wings) are compared with the simulated arrival time curves nearby, such as Figure 7 As shown in the figure, it is found that the simulated arrival time curves of these three points and their vicinity are intersecting and not parallel, so the assumed ε of the current layer is adjusted. r i value, adjust its value from 2 to 3, calculate the arrival time curves of the wave fields generated by each point source reaching the surface again and compare them, such as Figure 8 As shown in the figure, it is found that these three points are parallel to the simulated arrival time curves near them. At this time, it can be considered that the relative dielectric constant value ε r i =3 is the real value of the current layer value.

[0068] h. According to the real value of the current layer obtained in step g The time-depth conversion is performed again on the arrival time corresponding to the vertex of the diffraction wave currently being processed, and the depth is used as the bottom interface of the current layer. The current layer is recorded as L i (In theory, the number of layers should be consistent with the number of diffracted waves picked up);

[0069] i. Repeat steps d to h until the five diffraction waves picked up in step b are processed in sequence to obtain a complete layered model; for the portion deeper than the bottom interface of the layered model, set its relative dielectric constant value equal to the true relative dielectric constant value of the last layer.

[0070] j. The layered dielectric constant model obtained in step i is moderately smoothed to obtain the final relative dielectric constant model.

[0071] Example 2

[0072] a. Input the original record of Chang'e-4 lunar radar and adjust the round-trip travel time of the original record to the one-way travel time, that is, convert the original record time axis as a whole to half of the original value. The original lunar radar record round-trip travel time is 1000ns, and the converted one-way travel time is 500ns. Fig. 9 The purpose of this operation is to eliminate the influence of the curvature of the diffraction waves generated by the rock blocks in the lunar soil layer during the self-excitation and self-collection round-trip journey.

[0073] b. Manually select the identifiable diffraction waves in the one-way travel time record converted in step a. Since the size of the rock fragments or blocks distributed in the lunar soil layer is slightly smaller than or similar to the wavelength of the electromagnetic wave, the diffraction waves in the radar profile correspond to the interface with a larger bending amplitude (smaller curvature). Fig. 9 The white curve in the middle represents 31 identifiable diffraction waves manually selected from the Chang'e-4 lunar radar record. During the selection process, the recording segment where the diffraction wave is located is first extracted, and then the two points of the vertex and the two wings of the diffraction wave are picked up (such as Fig.10 shown).

[0074] c. Sort all the diffraction waves picked up in step b in order from small to large according to the corresponding vertices, and number them as ①, ②, ③, etc. like Fig.11 As shown;

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

[0076] e. Give a minimum relative permittivity value for the medium in the study area. A smaller relative permittivity value is also required as the assumed ε of the current layer r i value.

[0077] Conversion formula between velocity and relative dielectric constant:

[0078]

[0079] In the formula, c represents the propagation speed of electromagnetic waves 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 electromagnetic waves in the medium.

[0080] From the above conversion relationship, we can know that the given relative dielectric constant value ε r i Corresponding to a value greater than the maximum velocity of the medium in the study area A larger speed value v is required iCombined with the velocity from the surface to the previous layer, the time-depth conversion is performed on the arrival time corresponding to the vertex of the diffraction wave currently being processed. The depth obtained by the conversion is the maximum possible depth of the target body that generates the diffraction wave. If there is no previous layer, ε is assumed according to the current layer. r i The value is converted to time depth;

[0081] f. Between the depth and the surface, at the same horizontal position as the vertex of the diffraction wave currently being processed, select several points at equal intervals as the reference position of the target body that generates the diffraction wave. Taking the diffraction wave with the smallest vertex (numbered ①) as an example, at the same horizontal position as its vertex, select several points at equal intervals, such as Fig.12 As shown; taking several selected points as sources, combined with the relative dielectric constant value ε from the surface to the upper layer r i-1 value and the assumed ε of the current layer r i Based on the wavefront rapid advancement method, the arrival time curve of the wave field generated by each point source reaching the surface is calculated, such as Fig.13 shown. Fig.13 The black dashed lines in the middle represent the arrival time curves of the wave fields generated by each point source reaching the surface.

[0082] g. Compare the three points of the diffraction wave currently processed (the vertex and the two points on the two wings) picked up 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 r i The value is the real value of the current layer. If these three points are not parallel to the simulated arrival time curves near them, adjust the assumed ε of the current layer r i value, and repeat step f to match the two again, and repeat this process until the two are parallel. At this time, ε r i The value is the real value of the current layer. value;

[0083] Here, we still take the diffraction wave with the smallest peak (numbered ①) as an example. When the relative dielectric constant ε is assumed to be r i =3.5, the three points extracted from the diffraction wave numbered ① (the vertex and two points on the two wings) are compared with the simulated arrival time curves nearby, such as Fig.13 As shown in the figure, it is found that the simulated arrival time curves of these three points and their vicinity are intersecting and not parallel, so the assumed ε of the current layer is adjusted. r i The value is adjusted from 3.5 to 3.8, and the arrival time curves of the wave fields generated by each point source reaching the surface are calculated again and compared, such as Fig.14As shown in the figure, it is found that these three points are parallel to the simulated arrival time curves near them. At this time, it can be considered that the relative dielectric constant value ε r i =3.8 is the real value of the current layer value.

[0084] h. According to the real value of the current layer obtained in step g The time-depth conversion is performed again on the arrival time corresponding to the vertex of the diffraction wave currently being processed, and the depth is used as the bottom interface of the current layer. The current layer is recorded as L i (In theory, the number of layers should be consistent with the number of diffracted waves picked up);

[0085] i. Repeat steps d to h until the 31 diffraction waves picked up in step b are processed in sequence, and a complete layered model is obtained; the relative dielectric constant value of the part deeper than the bottom interface of the layered model is set to be equal to the true relative dielectric constant value of the last layer, such as Fig.15 As shown;

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

[0087] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection 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, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A layer peeling velocity scanning method suitable for lunar radar data, characterized in that: The following steps are involved: a. Adjust the two-way travel time originally recorded by the radar to the one-way travel time; b. manually selecting identifiable diffraction waves in the one-way travel time record converted in step a; c. Sort and number all the picked diffraction waves in ascending order according to the time when the vertices correspond to them; d. Select the diffraction wave with the smallest vertex arrival time from all the unprocessed diffraction waves as the current processing object; e. Give a relative permittivity value smaller than the minimum relative permittivity value of the medium in the study area as the assumed relative permittivity value of the current layer; combine the velocity from the surface to the previous layer, and perform time-depth conversion on the arrival time corresponding to the vertex of the diffraction wave currently being processed. The depth obtained by the conversion is the maximum possible depth corresponding to the target body that generates the diffraction wave; if there is no previous layer, perform time-depth conversion according to the assumed relative permittivity value of the current layer; f. Between the depth and the surface, at the same horizontal position as the vertex of the diffraction wave currently being processed, select several points at equal intervals as the reference positions of the target body that generates the diffraction wave; using the selected points as sources, combining the relative dielectric constant value from the surface to the previous layer and the assumed relative dielectric constant value of the current layer, based on the wavefront rapid advancement method, calculate the arrival time curve of the wave field generated by each point source to the surface; g. Compare the arrival time curves of the wave fields generated by each point source in step f and the three points of the diffraction waves currently being processed picked up in step b; if the three points are parallel to the simulated arrival time curves near them, it can be considered that the assumed relative permittivity value is the true relative permittivity value of the current layer; if the three points are not parallel to the simulated arrival time curves near them, readjust the assumed relative permittivity value of the current layer, and repeat step f to match the two again; repeat this process until the two are parallel, and obtain the true relative permittivity value of the current layer; h. According to the real relative dielectric constant value of the current layer obtained in step g, the time-depth conversion is performed again on the arrival time corresponding to the vertex of the diffraction wave currently being processed, and the depth is taken as the bottom interface of the current layer; i. Repeat steps d to h until all the numbered diffraction waves in step b are processed in sequence, i.e., a complete layered model is obtained; the relative dielectric constant value of the portion deeper than the bottom interface of the layered model is set equal to the relative dielectric constant value of the last layer; j. Moderately smooth the layered model of step i to obtain the final relative dielectric constant model.

2. The layer peeling velocity scanning method suitable for lunar exploration radar data according to claim 1, characterized in that: Step b: During the selection process, firstly extract the recording segment where the diffraction wave is located, and then pick up the two points of the vertex and the two wings of the diffraction wave.

3. The layer peeling velocity scanning method suitable for lunar exploration radar data according to claim 1, characterized in that: Step d, the smallest diffraction wave at the vertex is the diffraction wave with the smallest number.

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

5. The layer peeling velocity scanning method applicable to lunar exploration radar data according to claim 1, characterized in that: Step g, the three points are the vertex and two points on the two wings.

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