Asteroid internal dielectric constant estimation method and device based on single-station orbit radar

Abstract

The invention discloses an asteroid internal dielectric constant estimation method and device based on a single-station orbit radar, and relates to the field of planet detection, and the method mainly comprises the steps: separating diffracted waves from a single-station orbit radar record, and determining the number of diffraction points in an asteroid and the value range of a scanning dielectric constant; setting a diffraction point and a scanning dielectric constant value in the asteroid, solving the eikonal equation to obtain diffracted wave travel time, and calculating superposition energy of diffracted waves in a fixed time window from the travel time; the previous step is repeated until all positions in the asteroid are traversed, and the value range of the dielectric constant is scanned; selecting a plurality of local maximum values from all the superposed energy, and determining diffraction point positions and scanning dielectric constant values corresponding to all the maximum values; and interpolating the result to obtain the internal dielectric constant distribution of the asteroid. According to the asteroid internal dielectric constant estimation method and device based on the single-station orbit radar, the distribution of the internal dielectric constants of the asteroid can be rapidly and accurately obtained.

Description

Technical Field

[0001] The present invention relates to the field of planetary exploration, and more specifically, to a method and device for estimating the internal dielectric constant of an asteroid based on a single-station orbital radar. Background Art

[0002] In recent years, deep space exploration activities in the solar system have been in the ascendant, and asteroid exploration has become the main development direction. The asteroid exploration mission includes determining the orbital parameters, rotation parameters, shape, size, thermal radiation and other physical parameters of the asteroid, detecting the morphology, surface material composition, and internal structure of the asteroid, and conducting laboratory analysis and research on the returned samples, and determining the physical properties, chemical and mineral composition, isotopic composition and internal structure of the asteroid samples. Among them, the measurement of the dielectric constant of the surface and subsurface of the asteroid will not only help to deeply understand the internal structure and material composition of the asteroid, but also further reveal the origin and evolution of the asteroid and even the solar system.

[0003] It is reported that my country plans to implement its first small body exploration mission, the Tianwen-2 mission, in the first half of 2025. The mission aims to conduct companion exploration and sample return exploration of the near-Earth asteroid 2016 HO3. By then, the single-station orbital radar carried by the Tianwen-2 probe will conduct scientific exploration of the internal material composition of the asteroid 2016 HO3. Therefore, how to use the Tianwen-2 single-station orbital radar records to invert the internal dielectric constant of the asteroid is a technical problem that needs to be solved urgently. At present, the full waveform inversion and tomography inversion technologies in ground penetrating radar are expected to achieve the inversion of the internal dielectric constant distribution of the asteroid using the Tianwen-2 single-station orbital radar records, but these two inversion methods are extremely dependent on the initial model (dielectric constant and conductivity model). If the initial model is inaccurate, the inversion result will fail. In addition, these two methods also have the problems of large computational requirements and low efficiency. Therefore, it is crucial.

[0004] In the field of planetary vehicle-borne radar (Mars rover detection radar and lunar rover detection radar), the existing methods for estimating the dielectric constant of the interior of a planet mainly include the hyperbola fitting method, the three-dimensional velocity spectrum analysis method, the optimized hyperbola fitting method, etc. However, these methods have two main problems: (1) Most of these methods assume that the antenna is close to the surface of the moon or Mars, and do not consider the height of the planetary vehicle-borne radar antenna to the ground and the spacing between the transmitting and receiving antennas. In the actual Tianwen-2 orbital radar observation, the distance between the orbital radar antenna and the asteroid surface is relatively far, and there is also a certain distance between the transmitting and receiving antennas. These two factors cannot be ignored when estimating the dielectric constant of the interior of an asteroid; (2) Conventional methods for estimating the dielectric constant of the interior of a planet are all for the ground single-line observation system, while the Tianwen-2 single-station orbital radar is in the orbiting companion observation mode when detecting asteroids. There are obvious differences in the radar records obtained by the two different observation methods, and the difference in the morphological characteristics of the diffraction waves is even more significant. Therefore, the conventional dielectric constant estimation methods in the field of planetary vehicle-borne radar detection are not applicable to the dielectric constant estimation task of the Tianwen-2 single-station orbital radar records. In order to better serve the Tianwen-2 asteroid exploration mission, it is very necessary to study a set of methods suitable for single-station orbital radar that can quickly and accurately obtain the internal dielectric constant distribution of asteroids. Summary of the invention

[0005] The purpose of the present invention is to provide a method and device for estimating the internal dielectric constant of an asteroid based on a single-station orbital radar, which can quickly and accurately obtain the internal dielectric constant distribution of an asteroid.

[0006] The present invention provides a method for estimating the internal dielectric constant of an asteroid based on a single-station orbital radar, comprising the following steps: A1: preprocessing the single-station orbital radar record to obtain the single-station orbital radar record containing only diffraction waves, the number of diffraction points and a fixed time window; A2: obtaining the spatial grid spacing, the numerical simulation calculation area, the grid number and the grid number range where the internal area of ​​the asteroid is located according to the asteroid shape information, the orbital radar observation system and the antenna center frequency; A3: dividing the value range of the internal dielectric constant of the asteroid according to the preset dielectric constant scanning interval number to obtain a scanning dielectric constant sequence; A4: selecting a grid from the grid number range where the internal area of ​​the asteroid is located in the order from small to large as the diffraction point position and dividing the grid number range according to the preset dielectric constant scanning interval number; and A scanning dielectric constant value is selected from the scanning dielectric constant sequence in ascending order as the internal dielectric constant of the asteroid, the travel time of the diffraction wave is obtained by solving the Eikonal equation, the superposition energy of the diffraction wave in a fixed time window starting from the travel time of the diffraction wave in the single-station orbit radar record containing only the diffraction wave is calculated, and the diffraction wave superposition energy, diffraction point position and scanning dielectric constant value at this time are saved; A5: return to step A4 until the grid number range where the internal area of ​​the asteroid is located and the entire scanning dielectric constant sequence are traversed, and local maximum values ​​are selected from all the diffraction wave superposition energies. The number of local maximum values ​​is the number of diffraction points, and the diffraction point positions and scanning dielectric constant values ​​corresponding to the local maximum values ​​are selected; A6: The diffraction point positions and scanning dielectric constant values ​​corresponding to the local maximum values ​​are spatially interpolated to obtain the internal dielectric constant distribution of the asteroid.

[0007] Furthermore, step A1 specifically includes: A11: cutting off the direct wave in the single-station orbit radar record to obtain the single-station orbit radar record after the direct wave is cut off; A12: separating the reflected wave in the single-station orbit radar record after the direct wave is cut off to obtain the separated single-station orbit radar record; A13: separating the multiple waves in the separated single-station orbit radar record to obtain the single-station orbit radar record containing only the diffraction wave and the diffraction wave; A14: according to the waveform characteristics of the diffraction wave, obtaining the number of diffraction points and the maximum duration of the diffraction wave; according to the maximum duration of the diffraction wave and the time sampling interval, obtaining the fixed time window.

[0008] Furthermore, step A2 specifically includes: calculating the spatial grid spacing, such as the formula:

[0009] in, represents the spatial grid spacing in the X direction, represents the speed of electromagnetic waves in vacuum, represents the dielectric constant of the asteroid interior, represents the center frequency of the orbital radar antenna; similarly, the spatial grid spacing in other directions can also be calculated using the above formula; according to the asteroid shape information, the orbital radar observation system and the spatial grid spacing, the numerical simulation calculation area is obtained; according to the spatial grid spacing, the numerical simulation calculation area is divided into a series of discrete orthogonal regular grids and numbered in sequence to obtain the grid number, and according to the asteroid shape information, the number range of the grid where the asteroid's internal area is located is further obtained.

[0010] Further, step A4 specifically includes: A41: according to the number range of the grid where the numerical simulation calculation area and the inner area of ​​the asteroid are located, a grid point is selected from the inner area of ​​the asteroid grid number range in ascending order as the diffraction point; A42: according to the asteroid shape information, the orbital radar observation system and the diffraction point, a scanning dielectric constant value is selected from the scanning dielectric constant sequence in ascending order, and the eikonal equation is solved to obtain the diffraction wave travel time; A43: according to the diffraction wave travel time, the fixed time window and the single-station orbital radar record containing only the diffraction wave, the superposition energy of the diffraction wave in the fixed time window starting from the diffraction wave travel time is obtained; A44: return to step A42 until the superposition energy of the diffraction wave in the fixed time window starting from the diffraction wave travel time corresponding to all the scanning dielectric constant values ​​in the scanning dielectric constant sequence is calculated, and the corresponding diffraction wave superposition energy, diffraction point position and scanning dielectric constant value are saved.

[0011] Further, step A43 specifically includes: according to the travel time of the diffraction wave, the fixed time window and the single-station orbit radar record containing only the diffraction wave, obtaining the superposition energy of the diffraction wave in the fixed time window starting from the travel time of the diffraction wave, and the calculation formula is as follows:

[0012] in, Indicates The assumed diffraction point position and the The superposition energy of the diffraction waves corresponding to the scanning dielectric constant values, Indicates the energy expansion multiple, Indicates the number of radar channels in a single-station track radar record, Indicates that from step A42 based on The assumed diffraction point position and the The first one is selected from the travel time of the diffraction wave obtained by scanning the dielectric constant value. When the diffraction wave of the road travels, is the length of the fixed time window in step A2, The first recorded by a single-station orbital radar containing only diffraction waves The diffraction wave data The amplitude of the diffraction wave at each time sampling point.

[0013] The present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-mentioned method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar.

[0014] The present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps of the above-mentioned method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar are implemented.

[0015] The present invention also provides a computer program product, including a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar.

[0016] The method and device for estimating the internal dielectric constant of an asteroid based on a single-station orbital radar provided by the present invention have the following beneficial effects: The present invention separates diffraction waves from single-station orbit radar records to determine the possible number of diffraction points and the scanning dielectric constant range; based on the observation system and the asteroid shape information, a point is selected from the inside of the asteroid as the diffraction point and a scanning dielectric constant value is given, the travel time of the diffraction wave is obtained by solving the eikonal equation, and the superposition energy of the diffraction wave in a fixed time window starting from the travel time is calculated; the previous step is repeated until the dielectric constant scanning range and all positions inside the asteroid are traversed; a number of local maxima (equal to the number of diffraction points) are selected from all the superposition energies, and the scanning dielectric constants and diffraction point positions corresponding to all the maxima are determined; the result is interpolated to obtain the dielectric constant distribution inside the asteroid; the present invention can quickly and accurately obtain the dielectric constant distribution inside the asteroid, which is helpful for quickly analyzing the internal structure and material composition of the asteroid; in addition, the obtained dielectric constant distribution is used as the initial model of offset imaging and full waveform inversion, which can significantly improve the offset imaging and full waveform inversion effects, thereby providing a more reliable scientific basis for analyzing the internal structure and material composition of the asteroid. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which: Figure 1 It is a flow chart of the method for estimating the internal dielectric constant of an asteroid based on a single-station orbital radar provided by the present invention; Figure 2 It is a schematic diagram of a two-dimensional uniform asteroid model including three diffraction points and a single-station orbit radar observation system provided by the present invention; Figure 3 It is the 10 MHz Ricker wavelet and its amplitude spectrum used in the numerical simulation of the single-station orbit radar record provided by the present invention; Figure 4This is an example diagram of a simulated single-station orbit radar record obtained based on a two-dimensional uniform asteroid model including three diffraction points provided by the present invention; Figure 5 It is a diffraction wave superposition energy result diagram obtained by performing dielectric constant scanning on single-channel diffraction wave data provided by the present invention; Figure 6 It is a diffraction wave superposition energy result diagram obtained by scanning all diffraction waves based on 101 scanning dielectric constants and the inner region of the asteroid provided by the present invention; Figure 7 The present invention provides a method for obtaining a diffraction wave superposition energy horizontal slice including a diffraction point position by using the method of the present invention; Figure 8 is the real and estimated dielectric constant distribution diagram of the two-dimensional uniform asteroid model including three diffraction points provided by the present invention; Fig. 9 It is a structural block diagram of the computer device provided by the present invention. DETAILED DESCRIPTION

[0018] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0019] Figure 1 A schematic diagram of the method for estimating the internal dielectric constant of an asteroid based on a single-station orbital radar in this embodiment is shown. In this embodiment, the method for estimating the internal dielectric constant of an asteroid based on a single-station orbital radar includes the following steps: A1: Preprocess the single-station orbit radar record to obtain the single-station orbit radar record containing only diffraction waves, the number of diffraction points and the fixed time window; As an exemplary embodiment, in step A1, the single-station orbit radar record is preprocessed and the direct wave is removed, and the diffraction wave is separated from the single-station orbit radar record according to the difference in propagation characteristics of the reflected wave and the diffraction wave, and the number of diffraction points, the number of diffraction waves and the maximum duration are determined, and the length of the fixed time window should be slightly greater than the maximum duration; As an exemplary embodiment, step A1 specifically includes: A11: cutting off the direct wave in the single-station orbit radar record to obtain the single-station orbit radar record after the direct wave is cut off; A12: separating the reflected wave in the single-station orbit radar record after the direct wave is cut off to obtain the separated single-station orbit radar record; A13: separating the multiple waves in the separated single-station orbit radar record to obtain the single-station orbit radar record containing only the diffraction wave and the diffraction wave; A14: according to the waveform characteristics of the diffraction wave, obtaining the number of diffraction points and the maximum duration of the diffraction wave; according to the maximum duration of the diffraction wave and the time sampling interval, obtaining the fixed time window; It should be noted that the single-station orbit radar record referred to in step A1 is a simulated or actual radar record obtained by performing orbiting or hovering observation of an asteroid using an asteroid single-station detection radar with a fixed spacing between the transmitting and receiving antennas placed on the asteroid orbiter; A2: Based on the asteroid shape information, orbital radar observation system and antenna center frequency, the spatial grid spacing, numerical simulation calculation area, grid number and the grid number range of the asteroid interior area are obtained; As an exemplary embodiment, in step A2, the asteroid shape information is obtained in the following manner: first, basic asteroid shape data is obtained using photogrammetry (or laser point cloud ranging, photometry) technology, then a low-precision asteroid shape model is constructed based on image registration technology, and finally, a final high-precision asteroid shape model is generated using an iterative calculation method; As an exemplary embodiment, step A2 specifically includes: calculating the spatial grid spacing, such as the formula:

[0020] in, represents the spatial grid spacing in the X direction, represents the speed of electromagnetic waves in vacuum, represents the dielectric constant of the asteroid interior, represents the center frequency of the orbital radar antenna; similarly, the spatial grid spacing in other directions can also be calculated using the above formula; the numerical simulation calculation area is obtained according to the asteroid shape information, the orbital radar observation system and the grid spacing; according to the spatial grid spacing, the numerical simulation calculation area is divided into a series of discrete orthogonal regular grids and numbered in sequence to obtain the grid number, and the grid number range of the asteroid interior area is further obtained according to the asteroid shape information; It should be noted that the calculation area of ​​the numerical simulation is set to be 10–20 spatial grid spacings larger than the orbital altitude of the orbital radar; As an exemplary embodiment, in step A2, according to the orbital radar antenna center frequency, time sampling interval, observation system and asteroid shape information, a suitable numerical simulation calculation area and space grid spacing are selected, the calculation area is divided into a series of discrete orthogonal regular grids and numbered in sequence, and the grid number range corresponding to the asteroid internal area and the observation system (transmitting antenna and receiving antenna position) is determined; A3: Divide the dielectric constant value range inside the asteroid according to the preset dielectric constant scanning interval number to obtain a scanning dielectric constant sequence; As an exemplary embodiment, the preset number of dielectric constant scanning intervals is 100; It should be noted that the above range of the asteroid interior dielectric constant is obtained based on the travel time information of the reflected wave, the asteroid shape information and the observation system; A4: According to the numerical simulation calculation area, grid number, asteroid shape information and orbital radar observation system, select a grid from the grid number range where the asteroid's interior area is located in ascending order as the diffraction point position and select a scanning dielectric constant value from the scanning dielectric constant sequence as the asteroid's interior dielectric constant, solve the eikonal equation to obtain the diffraction wave travel time, calculate the superposition energy of the diffraction wave in a fixed time window starting from the diffraction wave travel time in the single-station orbital radar record containing only the diffraction wave, and save the diffraction wave superposition energy, diffraction point position and scanning dielectric constant value at this time; As an exemplary embodiment, in step A4, a discrete grid is selected from the discrete grid number range where the interior region of the asteroid obtained in step A2 is located as the diffraction point, and the dielectric constants of other regions of the interior of the asteroid except the diffraction point are set to the scanning dielectric constant values ​​in step A3 in sequence, and based on the observation system and the asteroid shape information, the diffraction wave travel times corresponding to all the scanning dielectric constant values ​​are obtained by solving the eikonal equation, and the superposition energy of the diffraction wave in a fixed time window starting from the diffraction wave travel time is calculated; As an exemplary embodiment, the detailed steps of step A4 include: A41: According to the numerical simulation calculation area and the grid number range of the asteroid's internal area, a grid point is selected from the grid number range of the asteroid's internal area in ascending order as the diffraction point; A42: According to the asteroid shape information, orbital radar observation system and diffraction point, select a scanning dielectric constant value from the scanning dielectric constant sequence in ascending order, solve the Eikonal equation, and obtain the diffraction wave travel time; As an exemplary embodiment, in step A42, the dielectric constants of the region inside the asteroid excluding the diffraction point are sequentially set to the scanning dielectric constant values ​​of the scanning dielectric constant value series in step A3, based on the observation system information, such as Figure 2 The coordinates of the red "o" and blue "×" in the figure, and the asteroid's shape information are as follows: Figure 2 The asteroid ellipse equation shown in the figure is used to solve the Eikonal equation to obtain the diffraction wave travel time corresponding to all the scanned dielectric constant values; A43: Based on the diffraction wave travel time, the fixed time window and the single-station orbit radar record containing only the diffraction wave, the superposition energy of the diffraction wave in the fixed time window starting from the diffraction wave travel time is obtained; As an exemplary embodiment, step A43 specifically includes: according to the travel time of the diffraction wave, the fixed time window and the single-station orbit radar record containing only the diffraction wave, obtaining the superposition energy of the diffraction wave in the fixed time window starting from the travel time of the diffraction wave, and the calculation formula is as follows:

[0021] in, Indicates The assumed diffraction point position and the The superposition energy of the diffraction waves corresponding to the scanning dielectric constant values, Indicates the energy expansion multiple, Indicates the number of radar channels in a single-station track radar record, Indicates that from step A42 based on The assumed diffraction point position and the The first one is selected from the travel time of the diffraction wave obtained by scanning the dielectric constant value When the diffraction wave of the road travels, is the length of the fixed time window in step A2, The first recorded by a single-station orbital radar containing only diffraction waves The diffraction wave data The amplitude of the diffraction wave at each time sampling point; It should be noted that in order to overcome the problem of small superposition energy change due to small amplitude of diffraction waves, The specific value of the energy amplification factor is flexibly set according to the diffraction wave amplitude; A44: Return to step A42 until the superposition energy of the diffraction waves in the fixed time window starting from the diffraction wave travel time corresponding to all the scanning dielectric constant values ​​in the scanning dielectric constant sequence is calculated, and the corresponding diffraction wave superposition energy, diffraction point position and scanning dielectric constant value are saved; As an exemplary embodiment, in step A44, steps A42 to A43 are repeated continuously until the diffraction wave superposition energy corresponding to all grid points inside the asteroid and the entire scanning dielectric constant sequence is obtained. , ,…, save the diffraction point positions and scanning dielectric constant values ​​corresponding to all diffraction wave superposition energies; A5: Return to step A4 until the grid number range of the inner region of the asteroid and the entire scanning dielectric constant sequence are traversed, and local maximum values ​​are selected from all the diffraction wave superposition energies. The number of local maximum values ​​is the number of diffraction points, and the diffraction point positions and scanning dielectric constant values ​​corresponding to the local maximum values ​​are selected; As an exemplary embodiment, in step A5, step A4 is repeated until the discrete grid number range where the inner region of the asteroid is located is traversed, a certain number (equal to the number of diffraction points) of local maximum values ​​are selected from all the obtained superposition energies, and the diffraction point positions and scanning dielectric constant values ​​corresponding to the local maximum values ​​are saved; A6: Perform spatial interpolation on the diffraction point positions and scanning dielectric constant values ​​corresponding to the local maxima to obtain the dielectric constant distribution inside the asteroid; As an exemplary embodiment, in step A6, spatial interpolation is performed based on the diffraction point positions and scanning dielectric constant values ​​corresponding to all local maxima obtained in step A5 to obtain the dielectric constant distribution inside the asteroid.

[0022] In some embodiments, the above-mentioned method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar is implemented in the following manner.

[0023] In an exemplary embodiment, a method for estimating the dielectric constant of an asteroid interior based on a single-station orbital radar includes: S1: separating diffraction waves from single-station orbital radar records, determining the possible number of diffraction points and the scanning dielectric constant range; S2: based on the observation system and asteroid shape information, selecting a point from the interior of the asteroid as the diffraction point and giving a scanning dielectric constant value, solving the eikonal equation to obtain the travel time of the diffraction wave, and calculating the superposition energy of the diffraction wave in a fixed time window starting from the travel time; S3: repeating the previous step until the dielectric constant scanning range and all positions inside the asteroid are traversed; S4: selecting a number of (equal to the number of diffraction points) local maxima from all superposition energies, and determining the scanning dielectric constants and diffraction point positions corresponding to all local maxima; S5: interpolating the results to obtain the dielectric constant distribution inside the asteroid.

[0024] In an exemplary embodiment, a flowchart of a method for estimating the internal dielectric constant of an asteroid based on a single-station orbital radar specifically includes the following steps: In the first step, the single-station orbital radar records are preprocessed and the direct waves are removed. The diffraction waves are separated from the single-station orbital radar records according to the differences in the propagation characteristics of the reflected waves and the diffraction waves. The number and maximum duration of the diffraction waves are determined, and the fixed time window length is set to be slightly larger than the maximum duration. The asteroid single-station orbit radar record used in this embodiment is a simulated single-station orbit radar record obtained based on a two-dimensional asteroid model containing three diffraction points (representing a lone rock asteroid); Figure 2 (a) and (b) show the dielectric constant and conductivity distribution of a uniform asteroid model with three diffraction points. Figure 2 As shown in (a), the asteroid model is a two-dimensional uniform asteroid model with three diffraction points inside. Its shape is elliptical, with the lengths of the major and minor axes being 60 meters and 40 meters respectively, and the grid spacing between the horizontal and vertical directions being 1 meter. The dielectric constant inside the asteroid is 4, and the conductivity is 1×10 −5 S / m; the area outside the asteroid is a vacuum with a dielectric constant of 1 and a conductivity of 0; the dielectric constant at the diffraction point is 6 and the conductivity is also 1×10 −5S / m; Transmitting antenna ( Figure 2 middle red "o") and the receiving antenna ( Figure 2 The middle blue "×") was placed sequentially at 30 positions in a circular orbit at an altitude of 90 meters from the center of the asteroid for radar observation; Figure 3 The 10 MHz Ricker wavelet and its amplitude spectrum used in the numerical simulation of the single-station orbital radar are recorded using Figure 3 The Ricker wavelet with a main frequency of 10 MHz is used as the excitation source, the time sampling interval is 1.5 ns, the recording time length is 1800 ns, and the fourth-order spatial and second-order temporal finite-difference time-domain algorithm is used to obtain the simulated single-station orbit radar record; like Figure 4 The following is a simulated single-station orbit radar record obtained based on a two-dimensional uniform asteroid model with three diffraction points. Figure 4 (a) shows the simulated single-station orbit radar record obtained by numerical simulation; (b) is the simulated single-station orbit radar record after cutting off the direct wave, (c) is the simulated single-station orbit radar record after cutting off the direct wave and the reflected wave, and (d) is the simulated single-station orbit radar record including only a single diffraction wave; Figure 4 The direct wave event axis of the simulated single-station orbital radar record shown in (a) is not horizontal. The reason is that the distance between the receiving and transmitting points is not strictly equal due to the large grid spacing of the model. In addition, due to the strong amplitude of the direct wave, the reflected wave and the diffracted wave are not clear enough, which is not convenient for the next step of dielectric constant estimation. In order to highlight the reflected wave and the diffracted wave, the direct wave in the simulated single-station orbital radar record is first cut off. Figure 4 (b) shows the simulated single-station orbit radar record after the direct wave is removed. From the figure, we can see that there are two reflection wave events with relatively strong amplitudes (located at 400ns and 1200ns, respectively, indicating the reflection waves from the asteroid surface closer and farther away from the observation point), and the diffraction wave events are still not clear enough; therefore, according to the difference in propagation characteristics of diffraction waves and reflection waves, Figure 4 The diffraction wave and the reflection wave in the simulated single-station orbit radar record in (b) are separated to obtain Figure 4 (c) shows the simulated single-station track radar record after removing the direct wave and reflected wave; Figure 4 In (c), we can find that there are three diffraction waves with different shapes in the time window from 600ns to 1200ns. Multiple waves begin to appear after 1200ns, and the amplitude of the multiple waves is relatively strong. In order to eliminate the influence of multiple waves on the estimation of the internal dielectric constant of the asteroid, Figure 4 In the simulated single-station orbital radar record shown in (c), the amplitude of the echo signal with a recording time greater than 1200ns is set to zero, that is, the synthetic orbital radar record containing only a single diffraction wave is shown in the result. Figure 4 As shown in (d), it can be determined from the figure that the number of diffraction points is 3; according to Figure 4 The waveform characteristics of the diffraction wave shown in FIG. 1 show that the maximum duration of the diffraction wave is about 208 ns, and the time sampling interval used in the simulation is 1.5 ns. Therefore, the fixed time window length of this embodiment is 210 ns. The second step is to select the appropriate numerical simulation calculation area and spatial grid spacing according to the orbital radar antenna center frequency, time sampling interval, observation system and asteroid shape information, divide the calculation area into a series of discrete orthogonal regular grids and number them in sequence, and determine the grid number range corresponding to the asteroid internal area and observation system (transmitting antenna and receiving antenna position); The third step is to use the travel time information of the reflected wave in the single-station orbital radar record to preliminarily estimate the range of the dielectric constant inside the asteroid based on the observation system and the asteroid's shape information, and select appropriate intervals to divide the dielectric constant range into a series of equally spaced scanning dielectric constant values; The center frequency of the single-station orbit radar antenna in this embodiment is 10 MHz, the shape of the two-dimensional asteroid model is an ellipse (the lengths of the major and minor axes are 40 m and 28 m respectively), and the circular orbit height of the single-station orbit radar is 90 m from the asteroid model. Therefore, the maximum size of the entire calculation interval in the horizontal and vertical directions is set to 200 m. The center frequency of the single-station orbital radar antenna and the two-dimensional asteroid model shape information in this embodiment, the discrete grid spacing of the asteroid model is 1, and the entire asteroid model occupies a total of 3681 grids, which are numbered 1, 2, ..., 3680, 3681 in sequence; according to Figure 4 The time position of the reflected wave event axis shown in (b) is combined with the observation system information and the asteroid shape information, and the relationship between the distance from the transmitting and receiving antenna to the asteroid surface, the internal dielectric constant and the electromagnetic wave propagation time is used to preliminarily estimate the distribution range of the asteroid's internal dielectric constant. , the number of intervals of scanning dielectric constant is set to 100, then the interval is 0.078, and a total of 101 scanning dielectric constant values ​​are obtained, which are 1.2, 1.278, …, 8.922, and 9 respectively; The fourth step is to select a discrete grid from the discrete grid number range of the asteroid interior region in the first step as the diffraction point, and let the dielectric constants of the asteroid interior regions other than the diffraction point be the scanning dielectric constant values ​​in the third step, and based on the observation system and the asteroid shape information, obtain the diffraction wave travel times corresponding to all the scanning dielectric constant values ​​by solving the eikonal equation, and calculate the diffraction wave superposition energy in the fixed time window corresponding to all the travel times; specifically, the following steps are included: Step (I): Select a discrete grid from the discrete grid number range where the interior region of the asteroid is located (for example, the grid point numbered 1 in the third step, i.e. Figure 2The leftmost grid point in the inner region of the asteroid model) is used as the diffraction point; Step (2): Let the dielectric constants of the asteroid's interior, excluding the diffraction point, be the scanned dielectric constant values ​​in step 3, based on the observation system information ( Figure 2 The coordinates of the red "o" and blue "×" in the figure), the asteroid's appearance information ( Figure 2 The asteroid ellipse equation shown in Figure 2 is obtained by solving the Eikonal equation to obtain the diffraction wave travel time corresponding to all the scanned dielectric constant values; Figure 4 For the waveform data of the seventh track (i.e., the seventh observation point) recorded by the single-station orbit radar containing only diffraction waves shown in (a), 101 different travel times are obtained according to 101 scanning dielectric constant values, see Figure 5 In (a), the blue filled square; Figure 5 The figure shows the velocity scan and superposition energy results of single-channel diffraction wave data; at this time, the diffraction point position is set to the grid point in the inner region of the asteroid numbered 1, and the relevant results of 101 scanning dielectric constant calculations are performed on the seventh observation point of the diffraction wave data; (a) is the diffraction wave travel time obtained based on 101 scanning dielectric constants, (b) is the seventh waveform of the first diffraction wave marked with the diffraction wave travel time and the fixed time window position, and (c) is the diffraction wave superposition energy result obtained based on 101 scanning dielectric constants; Step (iii): Based on the diffraction wave travel time corresponding to all the scanning dielectric constant values ​​obtained in step 2, calculate the radar signal superposition energy in a fixed time window starting from the travel time on the orbital radar profile corresponding to all the scanning dielectric constant values. The calculation formula is as follows:

[0025] in, Indicates The assumed diffraction point position and the The superposition energy of the diffraction waves corresponding to the scanning dielectric constant values, Indicates the energy amplification multiple (in order to overcome the problem of small superposition energy change due to small diffraction wave amplitude, the specific value is flexibly set according to the diffraction wave amplitude). Indicates the number of radar channels in a single-station track radar record, Indicates that based on The assumed diffraction point position and the The first one is selected from the travel time of the diffraction wave obtained by scanning the dielectric constant value The travel time of the diffracted wave is is the length of the fixed time window, For the The diffraction wave data The amplitude of the diffraction wave at each time sampling point; Step 4: Repeat steps 2 to 3 until the diffraction wave superposition energy corresponding to all scanned dielectric constant values ​​is obtained. , , …, save the diffraction point positions and scanned dielectric constant values ​​corresponding to the superposition energy of all diffraction waves; like Figure 5 As shown in (b), the black curve is Figure 4 (d) shows a single-channel waveform of the diffraction wave data. The red rectangle represents the fixed time window, and the green dots represent the travel time of the diffraction wave calculated based on the first scan dielectric constant value. The superposition energy of the diffraction wave is calculated using the formula shown in step 1, that is, Figure 5 The first point (green point) of the blue filled square connection in (c) corresponds to an energy value of 0.7641; similarly, the diffraction wave superposition energy corresponding to the remaining 100 scanned dielectric constant values ​​can be obtained ( Figure 5 (c) The 2nd to 101st blue filled points), the red five-pointed star indicates the maximum value at this time; Step 5: Repeat step 4 until 3681 grids inside the asteroid model are traversed, and three local maxima are selected from the superposition energy values ​​of the diffraction waves. The corresponding diffraction point positions and scanning dielectric constant values ​​are saved, that is, the diffraction point positions corresponding to the three diffraction waves and the equivalent dielectric constant inside the asteroid. For this example, a total of 3681 grid points with 101 different scanning speed values ​​are obtained. In order to display the results more intuitively and accurately, the 3681 grid points in the inner region of the asteroid are placed in the corresponding positions in the 200×200 grid of the simulation area, and the superposition energy corresponding to the different scanning dielectric constant values ​​at each grid point is taken as the value on the Z axis. Figure 6 The three-dimensional graph of the diffraction wave superposition energy at these 3681 different points is shown, which is the result of the diffraction wave superposition energy obtained by scanning all diffraction waves based on 101 scanning dielectric constants and the interior area of ​​the asteroid, where (a) is a front view and (b) is an oblique view. Figure 1 , (c) is bevel cutting Figure 2 ; Figure 6 (a) shows a 3D plot of the complete result. Figure 6 (b) and (c) show the three-dimensional images of the results of the resection; from Figure 6 Three local maxima are extracted from the three-dimensional data volume of the diffraction wave superposition energy shown in (a). The coordinate positions corresponding to the local maxima are (86, 96, 4.476), (101, 109, 4.008) and (112, 102, 3.54), respectively. The position information of these three points is the estimated position of the three diffraction points inside the asteroid and the corresponding dielectric constant; Figure 7The horizontal slice of the diffraction wave superposition energy including the diffraction point position is obtained by using the method of the present invention; (a) is the result of diffraction point 1, and the corresponding scanning dielectric constant is 4.476; (b) is the result of diffraction point 2, and the corresponding scanning dielectric constant is 4.008; (c) is the result of diffraction point 3, and the corresponding scanning dielectric constant is 3.540; the red "+" and the black "+" represent the real position and the estimated position of the diffraction point respectively; the blue "×" and the red "o" represent the receiving antenna position and the transmitting antenna position respectively; Figure 7 (a), (b), and (c) show horizontal slices of diffraction wave superposition energy with relative dielectric constants of 4.476, 4.008, and 3.54 respectively, which are cut from the diffraction wave superposition energy three-dimensional data volume; Figure 7 The estimated position of the mid-diffraction point (black “+”) is close to the true position (red “+”), and both are located at the local maximum of the superposition energy, indicating that the method is correct; The sixth step is to obtain the distribution of the dielectric constant inside the asteroid by spatial interpolation based on the diffraction point positions corresponding to all diffraction waves and the equivalent dielectric constant value inside the asteroid. The results are as follows: Figure 8 As shown in (b); Figure 8 The true and estimated dielectric constant distribution of the two-dimensional uniform asteroid model with three diffraction points; (a) is the true dielectric constant distribution, (b) is the estimated dielectric constant distribution; the red "+" and black "+" represent the true and estimated positions of the diffraction points, respectively; the blue "×" and red "o" represent the receiving antenna position and the transmitting antenna position, respectively; Table 1 shows the comparison between the estimated and true values ​​of the diffraction point positions and the dielectric constant inside the asteroid; Table 1: Comparison between the diffraction point position and the estimated and true values ​​of the dielectric constant of the asteroid interior in the two-dimensional asteroid model dielectric constant estimation example

[0026] from Figure 8 As can be seen from Table 1, the estimated positions of the three diffraction points are close to the actual positions, and the estimated results of the dielectric constant distribution inside the asteroid ( Figure 8 (b)) and the actual situation ( Figure 8 The maximum absolute error of the dielectric constant estimation result is about 0.5, the average relative error of the estimation result is only 14.2%, and the structural similarity (SSIM) coefficient of the image quality of the estimation result is 0.81, indicating that the method of the present invention can obtain a more accurate distribution of the internal dielectric constant of the asteroid. The method is effective and reliable, and is expected to provide method support for the actual asteroid single-station orbit radar data processing and inversion.

[0027] This embodiment provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the above-mentioned method for estimating the internal dielectric constant of an asteroid based on a single-station orbital radar are implemented. The storage medium may be a magnetic disk, an optical disk, a read-only memory (ROM), a random access memory (RAM), a flash memory, a hard disk (HDD), or a solid-state drive (SSD), etc.; the storage medium may also include a combination of the above-mentioned types of memory.

[0028] This embodiment provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps of the above-mentioned method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar are implemented.

[0029] like Fig. 9 As shown, the computer device may include: at least one processor 121, such as a central processing unit (CPU), at least one communication interface 123, a memory 124, and at least one communication bus 122. Among them, the communication bus 122 is used to realize the connection and communication between these components. Among them, the communication interface 123 may include a display screen (Display), a keyboard (Keyboard), and the optional communication interface 123 may also include a standard wired interface and a wireless interface. The memory 124 may be a high-speed random access memory (Random Access Memory, RAM), or a non-volatile memory (non-volatile memory), such as at least one disk storage. The memory 124 may also be at least one storage device located away from the aforementioned processor 121. Among them, the memory 124 stores an application program, and the processor 121 calls the program code stored in the memory 124 to perform any of the above method steps. Among them, the communication bus 122 may be a peripheral component interconnect (PCI) bus or an extended industry standard architecture (EISA) bus, etc. The communication bus 122 can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Fig. 9Only one line is used to represent it, but it does not mean that there is only one bus or one type of bus. Among them, the memory 124 may include a volatile memory (volatile memory), such as a random-access memory (random-access memory, RAM); the memory may also include a non-volatile memory (non-volatile memory), such as a flash memory (flash memory), a hard disk drive (hard disk drive, HDD) or a solid-state drive (solid-state drive, SSD); the memory 124 may also include a combination of the above-mentioned types of memory. Among them, the processor 121 may be a central processing unit (central processing unit, CPU), a network processor (network processor, NP) or a combination of CPU and NP. Among them, the processor 121 may further include a hardware chip. The above-mentioned hardware chip may be an application-specific integrated circuit (application-specific integrated circuit, ASIC), a programmable logic device (programmable logic device, PLD) or a combination thereof. The above-mentioned PLD may be a complex programmable logic device (complex programmable logic device, CPLD), a field-programmable gate array (field-programmable gate array, FPGA), a generic array logic (generic array logic, GAL) or any combination thereof. Optionally, the memory 124 is also used to store program instructions. The processor 121 can call the program instructions to implement the asteroid interior dielectric constant estimation method based on the single-station orbit radar as in this embodiment.

[0030] This embodiment provides a computer program product, including a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar.

[0031] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for estimating the internal dielectric constant of an asteroid based on a single-station orbital radar, characterized in that: The following steps are involved: A1: Preprocess the single-station orbit radar record to obtain the single-station orbit radar record containing only diffraction waves, the number of diffraction points and the fixed time window; A2: Based on the asteroid shape information, orbital radar observation system and antenna center frequency, the spatial grid spacing, numerical simulation calculation area, grid number and the grid number range of the asteroid interior area are obtained; A3: Divide the dielectric constant value range inside the asteroid according to the preset dielectric constant scanning interval number to obtain a scanning dielectric constant sequence; A4: According to the numerical simulation calculation area, grid number, asteroid shape information and orbital radar observation system, a grid is selected from the grid number range where the interior area of ​​the asteroid is located in ascending order as the diffraction point position and a scanning dielectric constant value is selected from the scanning dielectric constant sequence in ascending order as the interior dielectric constant of the asteroid, the eikonal equation is solved to obtain the diffraction wave travel time, the superposition energy of the diffraction wave in the fixed time window starting from the diffraction wave travel time in the single-station orbital radar record containing only the diffraction wave is calculated, and the diffraction wave superposition energy, the diffraction point position and the scanning dielectric constant value at this time are saved; A5: Return to step A4 until the grid number range where the inner region of the asteroid is located and the entire scanning dielectric constant sequence are traversed, and local maximum values ​​are selected from all the diffraction wave superposition energies. The number of the local maximum values ​​is the number of the diffraction points, and the diffraction point positions and scanning dielectric constant values ​​corresponding to the local maximum values ​​are selected; A6: Perform spatial interpolation on the diffraction point positions and scanning dielectric constant values ​​corresponding to the local maxima to obtain the dielectric constant distribution inside the asteroid.

2. The method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar according to claim 1, characterized in that: Step A1 specifically includes: A11: The direct wave in the single-station orbit radar record is cut off to obtain the single-station orbit radar record after the direct wave is cut off; A12: separating the reflected waves in the single-station track radar record after the direct wave is cut off to obtain a separated single-station track radar record; A13: separating the multiple waves in the separated single-station orbit radar record to obtain a single-station orbit radar record containing only diffraction waves and the diffraction waves; A14: According to the waveform characteristics of the diffraction wave, the number of diffraction points and the maximum duration of the diffraction wave are obtained; according to the maximum duration of the diffraction wave and the time sampling interval, a fixed time window is obtained.

3. The method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar according to claim 1, characterized in that: Step A2 specifically includes: calculating the spatial grid spacing, the formula is as follows: in, represents the spatial grid spacing in the X direction, represents the speed of electromagnetic waves in vacuum, represents the dielectric constant of the asteroid interior, represents the center frequency of the orbital radar antenna. Similarly, the spatial grid spacing in other directions can also be calculated using the above formula; A numerical simulation calculation area is obtained according to the asteroid shape information, the orbital radar observation system and the space grid spacing; According to the spatial grid spacing, the numerical simulation calculation area is divided into a series of discrete orthogonal regular grids and numbered in sequence to obtain grid numbers. According to the asteroid shape information, the number range of the grid where the internal area of ​​the asteroid is located is further obtained.

4. The method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar according to claim 1, characterized in that: Step A4 specifically includes: A41: According to the numerical simulation calculation area and the grid number range of the asteroid interior area, a grid point is selected from the grid number range of the asteroid interior area in ascending order as the diffraction point; A42: According to the asteroid shape information, the orbital radar observation system and the diffraction point, a scanning dielectric constant value is selected from the scanning dielectric constant sequence in ascending order, and the eikonal equation is solved to obtain the diffraction wave travel time; A43: obtaining the superposition energy of the diffraction wave in the fixed time window starting from the diffraction wave travel time according to the diffraction wave travel time, the fixed time window and the single-station orbit radar record containing only the diffraction wave; A44: Return to step A42 until the superposition energy of the diffraction wave within the fixed time window starting from the diffraction wave travel time corresponding to all the scanning dielectric constant values ​​in the scanning dielectric constant sequence is calculated, and the corresponding diffraction wave superposition energy, diffraction point position and scanning dielectric constant value are saved.

5. The method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar according to claim 4, characterized in that: Step A43 specifically includes: obtaining the superposition energy of the diffraction wave in the fixed time window starting from the diffraction wave travel time according to the diffraction wave travel time, the fixed time window and the single-station orbit radar record containing only the diffraction wave, and the calculation formula is as follows: in, Indicates The assumed diffraction point position and the The superposition energy of the diffraction waves corresponding to the scanning dielectric constant values, Indicates the energy expansion multiple, Indicates the number of radar channels in a single-station track radar record, Indicates that from step A42 based on The assumed diffraction point position and the The first one is selected from the travel time of the diffraction wave obtained by scanning the dielectric constant value When the diffraction wave of the road travels, is the length of the fixed time window in step A2, The first recorded by a single-station orbital radar containing only diffraction waves The diffraction wave data The amplitude of the diffraction wave at each time sampling point.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar as described in any one of claims 1 to 5 are implemented.

7. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar as described in any one of claims 1 to 5 are implemented.

8. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method for estimating the interior dielectric constant of an asteroid based on a single-station orbital radar as described in any one of claims 1 to 5 are implemented.

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