Modeling and simulation method of space-borne synthetic aperture radar echo under complex weather conditions

Abstract

The application discloses a kind of complex weather conditions under space-borne synthetic aperture radar echo modeling and simulation method, belong to radar signal processing and simulation technical field, for the problem that existing simulation method is difficult to accurately evaluate real non-uniform three-dimensional meteorological field to high frequency band SAR signal influence, the application first constructs three-dimensional meteorological scene using mesoscale numerical weather prediction model and extracts macroscopic microphysical parameter;Second, establish the off-line lookup table of nonspherical single particle electromagnetic scattering characteristics;Then, dynamically retrieve the precipitation particle size spectrum distribution of each meteorological grid, and calculate the extinction coefficient and volume backscattering coefficient of group particle body by table lookup integral calculation;Finally, based on ray tracing method, calculate two-way amplitude attenuation and slant range delay, combined with SAR echo model to generate two-dimensional original echo modulated by complex weather.The application can simulate the influence of complex weather on SAR signal with high fidelity and high efficiency, and provide support for SAR system design and weather attenuation correction.

Description

Technical Field

[0001] This invention belongs to the field of radar signal processing and simulation technology, specifically involving a method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions. Background Technology

[0002] Synthetic Aperture Radar (SAR) is an active microwave remote sensing device capable of achieving two-dimensional high-resolution imaging. With its all-weather, all-day operation, SAR plays a crucial role in topographic mapping, disaster assessment, and other fields. The substances in the atmosphere that cause electromagnetic wave signal attenuation and scattering are mainly clouds and precipitation particles, and their specific impact on electromagnetic waves depends on the phase and geometry of the particles. When radar operates at higher frequencies, the influence of various precipitation particles needs to be considered, especially in severe weather conditions, where clouds, rain, and other precipitation particles exhibit significant attenuation, delay, and meteorological clutter enhancement of higher-frequency electromagnetic waves. As spaceborne SAR systems gradually develop towards the X, Ku, and even higher frequency bands, the wavelength of electromagnetic waves has shrunk to the centimeter or millimeter scale, comparable to the size of larger precipitation particles in the atmosphere (such as raindrops and hail). When encountering complex meteorological conditions such as strong convection and heavy rain, high-frequency SAR signals will interact strongly with precipitation particles, causing severe signal attenuation, propagation delay and meteorological clutter interference, ultimately resulting in darkened targets, reduced resolution and even geometric distortion in SAR images.

[0003] Currently, echo simulation is an indispensable part of the design and imaging algorithm verification of spaceborne SAR systems. However, traditional SAR echo simulation methods have the following drawbacks: Oversimplification of meteorological scenarios: Existing simulations mostly focus on ideal vacuum scenarios. Even when meteorological factors are considered, precipitation scenarios are usually simplified to a single, spatially uniformly distributed attenuating medium, or empirical formulas such as those from ITU-R are directly used as substitutes. This approach fails to reflect the non-uniformity of the spatial distribution of real three-dimensional meteorological fields and ignores the combined effects of multi-phase particles such as clouds, rain, snow, and hail.

[0004] Inaccurate particle electromagnetic modeling: Traditional methods often calculate the scattering characteristics of precipitation particles based on ideal spheres. However, in real precipitation, large raindrops are flat, and hailstones have irregular, undulating surfaces. The spherical assumption cannot accurately reflect the differences in extinction and scattering of non-spherical particles under different polarization modes.

[0005] The computational complexity is extremely high: If the precise electromagnetic properties of each non-spherical particle are to be calculated in real time in a high-resolution 3D mesh, the amount of computation will increase exponentially, which is severely limited by computer memory and computing speed, making it difficult to achieve end-to-end simulation of SAR echoes in large scenes.

[0006] Therefore, it is necessary to design an accurate modeling and simulation method to accurately calculate the attenuation, scattering, and delay caused by meteorological factors, for use in echo simulation and meteorological correction. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, this invention provides a method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions. The technical problem to be solved by this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions, including: A three-dimensional meteorological scene grid of the target area was constructed using a mesoscale numerical weather prediction model, and the mass mixing ratio and particle number concentration of different precipitation particles in each meteorological scene grid were extracted as meteorological parameters. Based on phase characteristics, non-spherical geometric models of various precipitation particles are established. The T-matrix method is used to pre-calculate the single-particle extinction cross section and backscattering cross section of different equivalent particle sizes under different frequencies and polarization modes, and an offline single-particle electromagnetic scattering characteristic lookup table is generated. Based on the meteorological parameters, the parameters of the particle size distribution function of various precipitation particles are inverted within each meteorological scene grid; based on the single-particle electromagnetic scattering characteristic lookup table and the parameters of the particle size distribution function, the volume extinction coefficient and volume backscattering coefficient of each three-dimensional meteorological scene grid are obtained by grid integration and characteristic accumulation. Based on the ray tracing method, the slant range delay caused by the change in refractive index and the two-way amplitude attenuation caused by the accumulation of the volume extinction coefficient along the propagation path are calculated when the radar beam passes through a three-dimensional meteorological scene, according to the volume extinction coefficient. By using a pre-constructed total echo model that includes the superposition of surface backscattering and meteorological clutter, the slant range delay, two-way amplitude attenuation, and volume backscattering coefficient are processed to obtain the generated two-dimensional SAR raw echo that is modulated by meteorology.

[0008] In one embodiment of the present invention, the meteorological parameters further include: Atmospheric pressure, absolute temperature, and water vapor pressure for each meteorological scene grid.

[0009] In one embodiment of the present invention, a non-spherical geometric model of various precipitation particles is established based on phase characteristics, including: Non-spherical geometry is modeled using a rotationally symmetric ellipsoid, and liquid precipitation particles are modeled as rotationally symmetric ellipsoids. Non-spherical geometry modeling is performed using Chebyshev polynomial shapes, and solid precipitation particles are modeled as Chebyshev shapes.

[0010] In one embodiment of the present invention, based on the meteorological parameters, the parameters of the particle size distribution function of various precipitation particles are inverted within each meteorological scene grid, including: The distribution of particle swarms within a 3D meteorological scene grid is described using a three-parameter gamma distribution. Based on meteorological parameters and particle swarm distribution, inversion is performed using a preset inversion formula to obtain spectral slope parameters and spectral intercept parameters as parameters of the particle size distribution function.

[0011] In one embodiment of the present invention, the expression of the preset inversion formula is as follows: ; ; in, Indicates the spectral slope parameter. Indicates the spectral intercept parameter. Represents the gamma function. The preset shape factor representing the distribution of the particle swarm. Represents particle density, Indicates air density, Indicates the mass mixing ratio. This indicates the particle number concentration.

[0012] In one embodiment of the present invention, based on a single-particle electromagnetic scattering characteristic lookup table and parameters of the particle size distribution function, the volume extinction coefficient and volume backscattering coefficient of each three-dimensional meteorological scene grid are obtained by grid integration and characteristic accumulation, including: The single-particle electromagnetic scattering characteristic lookup table is called to obtain the cross-sectional values ​​at each particle size step, and the volume extinction coefficient of single particles in each grid is calculated by numerical integration. The volume extinction coefficients of all types of precipitation particles within each grid are summed to obtain the volume backscattering coefficient of that grid.

[0013] In one embodiment of the present invention, based on the ray tracing method, the slant range delay caused by the change in refractive index and the two-way amplitude attenuation caused by the accumulation of the volume extinction coefficient along the propagation path are calculated according to the volume extinction coefficient when the radar beam traverses a three-dimensional meteorological scene, including: Based on the atmospheric pressure, absolute temperature, and water vapor pressure of each meteorological scene grid, the total refractive index of the meteorological scene grid is calculated, and the slant range delay is obtained by integrating along the radar beam propagation path. The specific attenuation parameter is calculated based on the volume extinction coefficient, and the two-way amplitude attenuation is obtained by integrating along the radar beam propagation path.

[0014] In one embodiment of the present invention, the expression for the weather-modulated two-dimensional SAR raw echo is as follows: ; in, Indicates distance in advance time. Indicates direction in slow time. Indicates distance to fast time Direction and slow time The corresponding weather-modulated 2D SAR raw echo, Indicates distance to fast time Direction and slow time The corresponding two-dimensional baseband echo signal of a single-point surface target is modulated by both meteorological two-way attenuation and delay. Indicates distance to fast time Direction and slow time The corresponding total meteorological body scattered clutter signal within the scene, Indicates distance to fast time Direction and slow time The corresponding system thermal noise.

[0015] In a second aspect, the present invention provides an electronic device, including a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; The memory is used to store computer programs; When the processor executes the program stored in the memory, it implements the steps of the method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions provided in the first aspect of the present invention.

[0016] Thirdly, the present invention provides a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, it implements the steps of the method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions provided in the first aspect of the present invention.

[0017] The beneficial effects of this invention are: The solution provided in this invention breaks away from the traditional assumption of a homogeneous medium. Based on phase characteristics, it performs non-spherical modeling of various precipitation particles, accurately reproducing the two-way attenuation, polarization differences, and meteorological clutter interference of various complex particles on high-frequency SAR signals in real non-uniform precipitation scenarios. By designing a lookup-integration separation computational architecture, the most time-consuming non-spherical single-particle T-matrix calculation is separated into an offline lookup table. During 3D spatial grid simulation, only efficient particle size spectrum integration is required, solving the problem of excessive time consumption in complex meteorological SAR simulations. Furthermore, the echo model proposed in this invention comprehensively covers the multiplicative modulation, additive interference, and phase modulation of signals by meteorological factors, providing high-precision theoretical and data support for subsequent rainfall attenuation correction and imaging algorithm optimization. Attached Figure Description

[0018] Figure 1 A flowchart illustrating a method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions, provided in an embodiment of the present invention. Figures 2a-2b The simulation result diagram of the three-dimensional meteorological scene distribution used in the modeling and simulation method of spaceborne synthetic aperture radar echo under complex meteorological conditions provided in the embodiment of the present invention; Figures 3a-3b The table shows the scattering characteristics of non-spherical precipitation particles calculated under different particle sizes and frequencies in a modeling and simulation method for spaceborne synthetic aperture radar echoes under complex meteorological conditions provided in this embodiment of the invention. Figures 4a-4b The image shows the scene attenuation and volume scattering distribution calculated by the ray tracing method in a spaceborne synthetic aperture radar echo modeling and simulation method under complex meteorological conditions provided in an embodiment of the present invention. Figures 5a-5b The attenuation result diagram of the point target simulation verification imaging result in the spaceborne synthetic aperture radar echo modeling and simulation method under complex meteorological conditions provided in the embodiment of the present invention; Figures 6a-6b The delay result diagram of the point target simulation verification imaging result in the spaceborne synthetic aperture radar echo modeling and simulation method under complex meteorological conditions provided in the embodiment of the present invention; Figure 7 The simulation echo result of a surface target under complex meteorological conditions is shown in the embodiment of the present invention, which provides a method for modeling and simulating spaceborne synthetic aperture radar echo under complex meteorological conditions. Figure 8 The image shows the surface target imaging results under complex weather conditions, based on a spaceborne synthetic aperture radar echo modeling and simulation method provided in this embodiment of the invention. Figure 9 The image shows the imaging results of a spaceborne synthetic aperture radar echo modeling and simulation method under complex weather conditions provided in this embodiment of the invention, without being affected by complex weather conditions. Figure 10 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0020] To achieve the objectives, embodiments of the present invention provide a method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions, as well as electronic equipment and storage media.

[0021] Below, we will first introduce a method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions, as provided in the embodiments of the present invention.

[0022] like Figure 1 As shown in the embodiment of the present invention, a method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions may include the following steps: S1. A three-dimensional meteorological scene grid of the target area is constructed using a mesoscale numerical weather prediction model. The mass mixing ratio and particle number concentration of different precipitation particles in each meteorological scene grid are extracted as meteorological parameters.

[0023] Step S1 may specifically include the following steps: S11, Scene Selection and Preprocessing: Select the real weather process to be simulated, and use the WRF preprocessing system (WPS) to load static geographic data describing terrain height and grid meteorological data describing atmospheric state; use the geogrid, ungrib and metgrid modules in WPS to set the simulation center, map projection method and initial calculation grid, and generate intermediate preprocessed files containing three-dimensional meteorological field information and surface features.

[0024] S12, Nested Grid Design: A multi-layer nested grid method is adopted, which sets up three nested grids on the basis of the intermediate preprocessed file, so that the spatial resolution increases from the outer layer to the inner layer (for example, the resolutions are 9 km, 3 km and 1 km respectively) to obtain high-resolution meteorological details of the target center area.

[0025] S13, Physical Process Scheme Configuration: The Advanced Research WRF (ARW) dynamics core is selected, whose governing equations are based on the compressible non-hydrostatic atmospheric dynamics equations and adopts topographically followed hydrostatic mass vertical coordinates; the cloud microphysics scheme is configured as the Milbrandt-Yau dual-moment scheme to support the simultaneous forecasting of the mass mixing ratio and particle number concentration of multiple types of precipitation particles.

[0026] S14, Numerical simulation integral calculation: Call the WRF main program module (real.exe and wrf.exe) to convert the meteorological field into the terrain-following coordinate system, and iteratively solve the square equation according to the set time step to simulate the evolution of the meteorological scene.

[0027] S15, Macroscopic Microphysical Parameter Extraction: Extracting each grid cell from the high-resolution three-dimensional grid data output by numerical simulation. The mass mixing ratio of six types of precipitation particles: cloud droplets, raindrops, ice crystals, snow, graupel, and hail. and particle number concentration per unit volume Simultaneously, the total atmospheric pressure at each grid point is extracted. absolute temperature and water vapor pressure .

[0028] Meteorological parameters may also include: Atmospheric pressure, absolute temperature, and water vapor pressure for each meteorological scene grid.

[0029] S2. Based on the phase characteristics, establish non-spherical geometric models of various precipitation particles. Use the T matrix method to pre-calculate the single-particle extinction cross section and backscattering cross section of different equivalent particle sizes under different frequencies and polarization modes, and generate an offline lookup table of single-particle electromagnetic scattering characteristics.

[0030] Establishing non-spherical geometric models for various precipitation particles based on phase characteristics can include: Non-spherical geometry is modeled using a rotationally symmetric ellipsoid, and liquid precipitation particles are modeled as rotationally symmetric ellipsoids. Non-spherical geometry modeling is performed using Chebyshev polynomial shapes, and solid precipitation particles are modeled as Chebyshev shapes.

[0031] Step S2 may specifically include the following steps: S21, Non-spherical geometric modeling: Based on the physical phase characteristics of precipitation particles, liquid precipitation particles (cloud droplets, raindrops) are modeled as rotationally symmetric ellipsoids, with their axial ratio and equivalent particle size... Related; solid precipitation particles (ice, snow, graupel, hail) are modeled as Chebyshev shapes with undulating surfaces, and their surface equations are expressed as follows: ,in The radius of the undisturbed sphere. The deformation coefficient is... It is the order.

[0032] S22, Calculation of complex permittivity of particles: The complex permittivity of pure water and pure ice at specific frequencies is calculated using the Debye model; for mixed-phase particles such as snow and graupel, the equivalent complex permittivity is calculated using the Maxwell-Garnett formula. .

[0033] S23, T-matrix electromagnetic calculation: Given the SAR's operating frequency and polarization (HH, VV), the T-matrix method is used to solve for the transformation matrix between the particle incident field and the scattered field, and then the electromagnetic transformation of a single particle at an equivalent particle size of... Extinction section at time and backscattering cross section .

[0034] S24, Lookup table generation: Traverse the typical particle size range of various precipitation particles (e.g., 0.01mm to 10mm), encapsulate the calculated cross-sectional data with "particle type-particle size-polarization mode" as the index, and generate an offline scattering characteristic lookup table.

[0035] S3, based on meteorological parameters, invert the parameters of the particle size distribution function of various precipitation particles within each meteorological scene grid; based on the single-particle electromagnetic scattering characteristic lookup table and the parameters of the particle size distribution function, obtain the volume extinction coefficient and volume backscattering coefficient of each three-dimensional meteorological scene grid through grid integration and characteristic accumulation.

[0036] Based on meteorological parameters, the parameters for retrieving the particle size distribution function of various precipitation particles within each meteorological scene grid can include: The distribution of particle swarms within a 3D meteorological scene grid is described using a three-parameter gamma distribution. Based on meteorological parameters and particle swarm distribution, inversion is performed using a preset inversion formula to obtain spectral slope parameters and spectral intercept parameters as parameters of the particle size distribution function.

[0037] Among them, the three-parameter gamma distribution is The preset shape factor in the distribution of the particle swarm The value of can range from 0 to 3, and the expression of the preset inversion formula is as follows: ; ; in, Indicates the spectral slope parameter. Indicates the spectral intercept parameter. Represents the gamma function. The preset shape factor representing the distribution of the particle swarm. Represents particle density, Indicates air density, Indicates the mass mixing ratio. This indicates the particle number concentration.

[0038] Based on the single-particle electromagnetic scattering characteristic lookup table and the parameters of the particle size distribution function, the volume extinction coefficient and volume backscattering coefficient of each three-dimensional meteorological scene grid are obtained through grid integration and characteristic accumulation, which may include: The cross-sectional values ​​at each particle size step were obtained by calling the single-particle electromagnetic scattering property lookup table, and the volume extinction coefficient of single-type particles in each grid was calculated using numerical integration. ; ; The volume extinction coefficients of all types of precipitation particles within each grid are summed to obtain the volume backscattering coefficient of that grid.

[0039] The total specific attenuation rate of the grid is obtained by summing the volume properties of all types of precipitation particles (clouds, rain, snow, etc.) within the grid. The unit is dB / km, and the overall backscattering coefficient. : ; .

[0040] in, This represents the calculated extinction cross section for different types of particles at a particle size of D. This represents the number of different types of particles at a particle size of D. This represents the maximum particle size for each individual particle. This represents the minimum particle size for each individual particle. This represents the calculated backscattering coefficients of different types of particles with a particle size of D.

[0041] S4, based on the ray tracing method, calculates the slant range delay caused by refractive index changes and the two-way amplitude attenuation caused by the accumulation of the volume extinction coefficient along the propagation path when the radar beam traverses a three-dimensional meteorological scene, according to the volume extinction coefficient. This may include: Based on the atmospheric pressure of each meteorological scene grid absolute temperature and water vapor pressure Calculate the total refractive index of the weather scene grid. The slant range delay is obtained by integrating along the radar beam propagation path. ; The specific attenuation parameter is calculated based on the volume extinction coefficient, and the two-way amplitude attenuation is obtained by integrating along the radar beam propagation path. .

[0042] in, , , , Indicates the total specific decay rate. This represents the upper limit of the integral diameter set for different particles.

[0043] S5 utilizes a pre-constructed total echo model that includes the superposition of surface backscattering and meteorological clutter to process the slant range delay, two-way amplitude attenuation, and volume backscattering coefficient, thereby generating a two-dimensional SAR raw echo that is modulated by meteorology.

[0044] Step S5 may specifically include the following steps: S51, Calculation of Meteorological Modulation Echoes from Surface Targets: Assume the SAR system transmits a linear frequency modulated (LFM) signal, and the ideal slant range history of the surface target is... Due to the influence of complex weather conditions, the echoes from surface targets not only experience amplitude attenuation but also additional slant range delay. This results in envelope offset and carrier phase error. The expression for the two-dimensional baseband echo signal of a single-point surface target, modulated by both meteorological two-way attenuation and delay, is as follows: ; in, Indicates distance in advance time. Indicates direction in slow time. Indicates distance to fast time Direction and slow time The corresponding two-dimensional baseband echo signal of a single-point surface target is modulated by both meteorological two-way attenuation and delay. The complex backscattering coefficient of a surface target. This indicates the two-way amplitude attenuation. Represents the range-direction transmitted pulse envelope (e.g., a rectangular window). This represents the modulation envelope of the azimuth antenna pattern. Indicates the radar operating wavelength. The ideal slant range history representing a surface target Indicates slant range delay. Indicates the range-direction linear frequency modulation slope. It represents the speed of light.

[0045] S52, the volume backscattering coefficient of the three-dimensional meteorological grid calculated in step S4 is equivalent to the spatially discrete meteorological clutter scattering centers. Echo signal from a meteorological clutter scattering center Expressed as: ; in, The equivalent clutter complex amplitude is determined by both the volume backscattering coefficient and the grid volume of the grid. This represents the slant range history of the radar reaching this meteorological grid point. It also includes the total meteorological body scattered clutter signal within the scene. The superposition of the scattering center echoes from all meteorological grids: .

[0046] S53, Total Raw Echo Synthesis: Combines the surface target echo matrix modulated by meteorology, the meteorological body scattered clutter matrix, and the system thermal noise. The data is superimposed to generate a weather-modulated 2D SAR raw echo. : ; in, Indicates distance in advance time. Indicates direction in slow time. Indicates distance to fast time Direction and slow time The corresponding weather-modulated 2D SAR raw echo, Indicates distance to fast time Direction and slow time The corresponding two-dimensional baseband echo signal of a single-point surface target is modulated by both meteorological two-way attenuation and delay. Indicates distance to fast time Direction and slow time The corresponding total meteorological body scattered clutter signal within the scene, Indicates distance to fast time Direction and slow time The corresponding system thermal noise.

[0047] The effects of the embodiments of the present invention will be further explained below with reference to simulation experiments.

[0048] Experimental conditions: Table 1 lists the WRF meteorological scene simulation parameters used in the simulation experiment of step S1 proposed in the embodiments of the present invention. The simulation parameter settings in Table 1 are to obtain the meteorological scene data distribution used to calculate the attenuation, scattering, and delay of the three-dimensional meteorological scene, including necessary parameters such as particle mixing ratio, particle number concentration, atmospheric pressure, and temperature.

[0049] Table 1. Simulation Parameters for WRF Weather Scenarios

[0050] Table 2 lists the parameters used in the SAR echo simulation in this embodiment of the invention. These parameters are used to verify the damage to the echo and imaging results of spaceborne SAR under complex weather conditions.

[0051] Table 2 SAR echo simulation parameters

[0052] Experiment content: 3D high-resolution meteorological scene simulation: In this embodiment of the invention, the first step is to perform a numerical simulation of a three-dimensional high-resolution meteorological scene. This corresponds to step S1 in the implementation steps. Using the publicly available WRF mode, after setting the parameters as shown in Table 1, the simulation results are obtained, as follows: Figures 2a-2b As shown, Figure 2a Corresponding particle mixing ratio distribution, Figure 2bThe corresponding particle number concentration distribution is shown. The particle mixing ratio is expressed in g / kg, representing the weight of precipitation particles per unit mass of air; the particle number concentration represents the total number of particles per unit volume of air. The purpose of this simulation is to obtain data on particle mixing ratios, particle number concentrations, air pressure, and temperature for different precipitation particles in a three-dimensional meteorological scene, serving as the data source for subsequent calculations. The WRF model used in this step is a publicly available method, and this step is a necessary condition for the implementation of subsequent steps.

[0053] Calculation of scattering characteristics of non-spherical precipitation particles: After obtaining the numerical distribution of the three-dimensional meteorological scene, this embodiment of the invention uses the T-matrix method to calculate the scattering characteristics of non-spherical precipitation particles, including the extinction cross section and scattering cross section of the particles. The results are as follows: Figures 3a-3b As shown, Figure 3a The results are the calculated extinction cross section of precipitation particles. Figure 3b The calculation results are for the particle scattering cross section of precipitation. The horizontal axis represents the particle size range in mm, and the vertical axis represents the simulation frequency in GHz. The value at each position represents the cross section value under the given particle size and frequency conditions. This method generates the offline single-particle electromagnetic scattering characteristic lookup table obtained in step S2 of the implementation steps.

[0054] Scene simulation: Figures 4a-4b This is a diagram showing the scene attenuation and volume scattering distribution calculated using the ray tracing method in an embodiment of the present invention. Figure 4a This is the attenuation amount for a two-way path. Figure 4b The backscattering coefficient distribution of the swarm particles is shown, where the horizontal axis represents the range sampling points and the vertical axis represents the azimuth sampling points. To further explain the specific reasons for the degradation of SAR imaging quality under complex meteorological conditions, the impact of meteorological two-way attenuation on point target imaging results is analyzed below. Point targets are placed at the same coordinates in the simulation scenario, and point target echo simulations are performed under ideal conditions and when only meteorological attenuation is considered. The echoes obtained in both cases are then imaged, and the results are shown below. Figures 5a-5b As shown, Figure 5a The original point target imaging results and amplitude, Figure 5b The image results and amplitude of the point target after meteorological attenuation are shown. By comparing the peak amplitude of the point target, considering only the effect of meteorological attenuation, the peak amplitude of the point target is significantly reduced compared to the original point target, and the amount of reduction is consistent with the theoretical two-way attenuation on the target's propagation path. This shows that the main impact of meteorological attenuation on the target is the reduction of echo energy, and the target peak attenuation is consistent with the corresponding two-way attenuation on the path, without causing a significant decrease in focusing quality.

[0055] Figures 6a-6bThis is a delay result diagram of the point target simulation verification imaging results in the experiment of verifying the imaging result offset under complex meteorological conditions in an embodiment of the present invention. Figure 6a The coordinates of the original point target center are... Figure 6b The coordinates of the point target center after slant range delay are given. After considering the meteorological slant range delay, the azimuth focus center position Y of the point target remains unchanged, but the range peak coordinate X shifts from the original 4973rd sampling point to the 4977th sampling point. This indicates that the slowing of phase velocity caused by the change in refractive index manifests as an overall translation of the target towards the far distance in the SAR image, leading to a deviation in target positioning. Comparing the theoretical results with the simulated offset, the simulated offset matches the theoretical calculation with a small error.

[0056] Figure 7 This is a simulated echo result image of a surface target under complex meteorological conditions, according to an embodiment of the present invention. Some areas of the echo show a darkening characteristic, which is a result of attenuation caused by meteorological factors. The echo data under complex meteorological conditions was imaged, and the imaging results are as follows. Figure 8 As shown. Meanwhile, in order to quantitatively assess the impact of meteorological factors on the results, imaging results of a control group unaffected by meteorological conditions and with all other parameters remaining consistent were also obtained, such as... Figure 9 As shown. By comparison Figure 8 and Figure 9 The imaging results show some irregular dark areas, which are caused by meteorological factors. To more clearly show the extent of the impact, the imaging area is magnified locally. Figure 9 The overall topographical trend of the simulated area can be clearly seen in the imaging results that are unaffected by weather conditions, while Figure 8 The imaging results for ground targets show some loss of detail, manifesting as uneven distribution of dark bands, making it impossible to obtain effective target information from the results. Furthermore, within the circled area, a small region exhibits higher imaging energy than its surroundings, appearing as a bright band. This is due to complex meteorological factors; the darker areas are caused by a significant reduction in the effective energy of electromagnetic waves during two-way propagation, while meteorological clutter exhibits stronger backscattering in areas with higher particle density, thus resulting in a small bright band in the image.

[0057] The embodiments of the present invention have the following advantages compared with the prior art: High simulation fidelity: The embodiments of this invention break the traditional assumption of a homogeneous medium, reconstruct the particle size spectrum using WRF microphysical parameters, and use the T matrix method to model precipitation particles as non-spherical, accurately restoring the two-way attenuation, polarization difference and meteorological clutter interference of various complex particles on high-frequency SAR signals in real non-uniform precipitation scenarios.

[0058] Significantly improved computational efficiency: This invention proposes a computational architecture that separates "table lookup-integration". The most time-consuming calculation of the non-spherical single-particle T matrix is ​​separated into an offline lookup table. During three-dimensional spatial mesh simulation, only efficient particle size spectrum integration is required, which can solve the problem of excessive time consumption in complex meteorological SAR simulation.

[0059] The physical mechanism is well-developed: The echo model of this invention comprehensively covers the multiplicative modulation (two-way attenuation), additive interference (volume scattering clutter), and phase modulation (geometric deformation caused by slant range delay) of meteorological factors on the signal, providing high-precision theoretical and data support for subsequent rainfall attenuation correction and imaging algorithm optimization.

[0060] Secondly, embodiments of the present invention also provide an electronic device, such as... Figure 10 As shown, it includes a processor 001, a communication interface 002, a memory 003, and a communication bus 004, wherein the processor 001, the communication interface 002, and the memory 003 communicate with each other through the communication bus 004. The memory is used to store computer programs; When the processor executes the program stored in the memory, it implements the steps of the method for modeling and simulating spaceborne synthetic aperture radar echo under any complex meteorological conditions provided in the first aspect of the present invention.

[0061] The communication bus mentioned in the above electronic devices can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. This communication bus can be divided into address bus, data bus, control bus, etc. For ease of illustration, only one thick line is used to represent it in the diagram, but this does not mean that there is only one bus or one type of bus.

[0062] The communication interface is used for communication between the aforementioned electronic devices and other devices.

[0063] The memory may include random access memory (RAM) or non-volatile memory (NVM), such as at least one disk storage device. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor.

[0064] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0065] The method provided in this invention can be applied to electronic devices. Specifically, the electronic device can be a desktop computer, a portable computer, a smart mobile terminal, a server, etc. No limitation is made herein; any electronic device that can implement this invention falls within the protection scope of this invention.

[0066] Thirdly, corresponding to the method for modeling and simulating spaceborne synthetic aperture radar echo under complex meteorological conditions provided in the first aspect, this embodiment of the invention also provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, it implements the steps of the method for modeling and simulating spaceborne synthetic aperture radar echo under any of the complex meteorological conditions provided in the first aspect of this invention.

[0067] For the electronic device / storage medium embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and relevant details can be found in the description of the method embodiments.

[0068] It should be noted that the electronic device and storage medium in the embodiments of the present invention are respectively electronic devices and storage media that apply the above-mentioned method for modeling and simulating spaceborne synthetic aperture radar echo under complex meteorological conditions. Therefore, all embodiments of the above-mentioned method for modeling and simulating spaceborne synthetic aperture radar echo under complex meteorological conditions are applicable to the device, electronic device and storage medium, and can achieve the same or similar beneficial effects.

[0069] It should be noted that, in the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions, characterized in that, include: A three-dimensional meteorological scene grid of the target area was constructed using a mesoscale numerical weather prediction model, and the mass mixing ratio and particle number concentration of different precipitation particles in each meteorological scene grid were extracted as meteorological parameters. Based on phase characteristics, non-spherical geometric models of various precipitation particles are established. The T-matrix method is used to pre-calculate the single-particle extinction cross section and backscattering cross section of different equivalent particle sizes under different frequencies and polarization modes, and an offline single-particle electromagnetic scattering characteristic lookup table is generated. Based on the meteorological parameters, the parameters of the particle size distribution function of various precipitation particles are inverted within each meteorological scene grid; Based on the single-particle electromagnetic scattering characteristic lookup table and the parameters of the particle size distribution function, the volume extinction coefficient and volume backscattering coefficient of each three-dimensional meteorological scene grid are obtained by grid integration and characteristic accumulation. Based on the ray tracing method, the slant range delay caused by the change in refractive index and the two-way amplitude attenuation caused by the accumulation of the volume extinction coefficient along the propagation path are calculated when the radar beam passes through a three-dimensional meteorological scene, according to the volume extinction coefficient. By using a pre-constructed total echo model that includes the superposition of surface backscattering and meteorological clutter, the slant range delay, two-way amplitude attenuation, and volume backscattering coefficient are processed to obtain the generated two-dimensional SAR raw echo that is modulated by meteorology.

2. The method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions according to claim 1, characterized in that, The meteorological parameters also include: Atmospheric pressure, absolute temperature, and water vapor pressure for each meteorological scene grid.

3. The method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions according to claim 1, characterized in that, Based on phase characteristics, non-spherical geometric models of various precipitation particles are established, including: Non-spherical geometry is modeled using a rotationally symmetric ellipsoid, and liquid precipitation particles are modeled as rotationally symmetric ellipsoids. Non-spherical geometry modeling is performed using Chebyshev polynomial shapes, and solid precipitation particles are modeled as Chebyshev shapes.

4. The method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions according to claim 1, characterized in that, Based on the meteorological parameters, the parameters of the particle size distribution function of various precipitation particles are retrieved within each meteorological scene grid, including: The distribution of particle swarms within a 3D meteorological scene grid is described using a three-parameter gamma distribution. Based on meteorological parameters and particle swarm distribution, inversion is performed using a preset inversion formula to obtain spectral slope parameters and spectral intercept parameters as parameters of the particle size distribution function.

5. The method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions according to claim 4, characterized in that, The expression for the preset inversion formula is as follows: ； ； in, Indicates the spectral slope parameter. Indicates the spectral intercept parameter. Represents the gamma function. The preset shape factor representing the distribution of the particle swarm. Represents particle density, Indicates air density, Indicates the mass mixing ratio. This indicates the particle number concentration.

6. The method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions according to claim 1, characterized in that, Based on the single-particle electromagnetic scattering characteristic lookup table and the parameters of the particle size distribution function, the volume extinction coefficient and volume backscattering coefficient of each three-dimensional meteorological scene grid are obtained through grid integration and characteristic accumulation, including: The single-particle electromagnetic scattering characteristic lookup table is called to obtain the cross-sectional values ​​at each particle size step, and the volume extinction coefficient of single particles in each grid is calculated by numerical integration. The volume extinction coefficients of all types of precipitation particles within each grid are summed to obtain the volume backscattering coefficient of that grid.

7. The method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions according to claim 2, characterized in that, Based on the ray tracing method, the slant range delay caused by refractive index changes and the two-way amplitude attenuation caused by the accumulation of the volume extinction coefficient along the propagation path are calculated when the radar beam traverses a three-dimensional meteorological scene, according to the volume extinction coefficient. These factors include: Based on the atmospheric pressure, absolute temperature, and water vapor pressure of each meteorological scene grid, the total refractive index of the meteorological scene grid is calculated, and the slant range delay is obtained by integrating along the radar beam propagation path. The specific attenuation parameter is calculated based on the volume extinction coefficient, and the two-way amplitude attenuation is obtained by integrating along the radar beam propagation path.

8. The method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions according to claim 1, characterized in that, The expression for the weather-modulated 2D SAR raw echo is as follows: ； in, Indicates distance in advance time. Indicates direction in slow time. Indicates distance to fast time Direction and slow time The corresponding weather-modulated 2D SAR raw echo, Indicates distance to fast time Direction and slow time The corresponding two-dimensional baseband echo signal of a single-point surface target is modulated by both meteorological two-way attenuation and delay. Indicates distance to fast time Direction and slow time The corresponding total meteorological body scattered clutter signal in the scene, Indicates distance to fast time Direction and slow time The corresponding system thermal noise.

9. An electronic device, characterized in that, It includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; The memory is used to store computer programs; When the processor executes the program stored in the memory, it implements the steps of the method for modeling and simulating spaceborne synthetic aperture radar echo under complex meteorological conditions as described in any one of claims 1-8.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for modeling and simulating spaceborne synthetic aperture radar echoes under complex meteorological conditions as described in any one of claims 1-8.

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