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CN-121997684-A - Dynamic rough sea surface coherent scattering three-scale hybrid modeling and simulation method

CN121997684ACN 121997684 ACN121997684 ACN 121997684ACN-121997684-A

Abstract

The invention relates to the field of electromagnetic scattering modeling simulation, in particular to a dynamic rough sea surface coherent scattering three-scale mixed modeling and simulation method, which comprises the steps of firstly inputting sea conditions and radar parameters, generating a dynamic sea surface physical field, dividing scattering seeds of large, medium and small scales, adopting deterministic geometric modeling for pixel-level large-scale components, adopting Monte Carlo sampling for wavelength-level medium-scale components, adopting statistical modeling for sub-wavelength-level small-scale components, then utilizing a smooth coherent Green function method with multi-layer steepest descent to calculate a propagation function, and finally carrying out coherent superposition on scattering contributions of different scales to obtain an integral scattering field.

Inventors

  • XU FENG
  • ZHANG SHUAI
  • WEI JIANGTAO

Assignees

  • 复旦大学

Dates

Publication Date
20260508
Application Date
20260122

Claims (10)

  1. 1. The method for modeling and simulating the three-scale mixing of the coherent scattering of the dynamic rough sea surface is characterized by comprising the following steps of: s1, generating a dynamic sea surface physical field according to input sea surface parameters and radar parameters; S2, dividing the generated sea surface into three components of a pixel level large scale, a wavelength level middle scale and a sub-wavelength level small scale, and generating a grid; s3, calculating a propagation function by using a multilayer steepest descent smooth coherent Green function method; S4, carrying out motion modeling and scattering modeling on each coherent scatterer; S5, carrying out coherent superposition on scattering contributions of all scales to obtain an integral sea surface scattering field; the sea surface parameters comprise sea surface geometric dimensions to be simulated, grid node numbers, friction wind speed, wind direction, peak wave period and sea wave direction spectrum; The radar parameters include carrier frequency, bandwidth, pulse repetition frequency, polarization, radar incidence angle, and radar azimuth angle.
  2. 2. The method for modeling and simulating three-dimensional hybrid coherent scattering on a dynamic rough sea surface according to claim 1, wherein the dynamic sea surface physical field in S1 is composed of a discrete quadrilateral mesh, and comprises a sea surface altitude field, a local gradient field and a track velocity field.
  3. 3. The method for modeling and simulating the three-scale hybrid coherent scattering of the dynamic rough sea surface according to claim 2, wherein the sea surface height field is numerically simulated by a linear wave superposition method, and the sea surface height is obtained by superposition of a plurality of plane forward wave components at any spatial position and moment; the local gradient field is obtained by calculating the partial derivative of the sea surface height field to the plane space coordinate, and comprises a gradient component along the first space coordinate direction and a gradient component along the second space coordinate direction; the orbital velocity field is obtained from the gradient of a velocity potential function in the spatial direction, the velocity potential function being related to gravitational acceleration, angular frequency, depth decay term and phase term.
  4. 4. The method for modeling and simulating the three-scale mixing of the coherent scattering of the dynamic rough sea surface, which is disclosed in claim 1, is characterized in that in the step S2, the condition that the generated sea surface is divided into sub-wavelength level small-scale components is that the characteristic scale of the sea surface is smaller than the wavelength of a radar carrier wave; the pixel-level large-scale component adopts deterministic geometric modeling, the wavelength-level mesoscale component adopts Monte Carlo sampling, and the sub-wavelength-level small-scale component adopts statistical modeling.
  5. 5. The method for modeling and simulating three-dimensional hybrid of coherent scattering on a dynamic rough sea surface according to claim 1, wherein the grid size in S2 is seven times the radar carrier wavelength.
  6. 6. The method for modeling and simulating three-dimensional hybrid coherent scattering on a rough sea surface according to claim 1, wherein the propagation function in the step S3 is obtained by accumulating a plurality of approximate saddle points obtained by multi-layer steepest descent item by item, and each accumulated item comprises an amplitude weight determined by the approximate saddle point, a complex exponential phase item determined by a phase function and a Hamming window function.
  7. 7. The method of three-scale hybrid modeling and simulation of coherent scattering on a rough sea surface according to claim 6, wherein the amplitude weight is determined by a hessian matrix of the phase function at an approximate saddle point; In each iteration, the wave vector of the next iteration is updated along the opposite direction of the phase function gradient according to a preset step length.
  8. 8. The method for modeling and simulating three-dimensional mixture of coherent scattering on a rough sea according to claim 1, wherein the modeling of the motion in S4 comprises: For each coherent scatterer, a velocity vector field is generated by a large-scale spectrum, and then the phase velocities of components corresponding to Bragg scattering parts are superimposed, wherein the directions of the phase velocities are consistent with the wave propagation directions.
  9. 9. The method for modeling and simulating three-dimensional hybrid of coherent scattering on a rough sea according to claim 1, wherein the modeling of scattering in S4 comprises: Calculating a large-scale scattering contribution and a small-scale Bragg scattering contribution for each coherent scatterer respectively; The amplitude of the large-scale scattering contribution is represented by an exponential attenuation form, and the attenuation relation of the amplitude is related to radar wave number, sea surface height standard deviation and radar incidence angle, and is related to sea surface large-scale scattering reflection coefficient amplitude and radar azimuth beam width; The amplitude of the small-scale Bragg scattering contribution is related to the radar wave number, the square of the amplitude of the polarized scattering matrix and the spectral value of the sea surface spectrum in the band direction at the Bragg wave number, and the small-scale Bragg scattering contribution simultaneously contains the spectral item contributions corresponding to the positive Bragg wave number and the negative Bragg wave number; The polarized scattering matrix is obtained by multiplying an incident and scattered polarized basis transformation matrix and a diagonal scattering coefficient matrix.
  10. 10. The method for modeling and simulating three-scale hybrid coherent scattering on a dynamic rough sea surface according to claim 1, wherein the overall sea surface scattering field of S5 is obtained by summing up complex scattering amplitudes of a large-scale scatterer, a medium-scale scatterer and a small-scale scatterer, respectively, and then performing coherent superposition.

Description

Dynamic rough sea surface coherent scattering three-scale hybrid modeling and simulation method Technical Field The invention relates to the field of electromagnetic scattering modeling simulation, in particular to a method for modeling and simulating three-scale mixing of coherent scattering of a dynamic rough sea surface. Background Sea electromagnetic scattering modeling has fundamental roles in sea remote sensing parameter inversion, sea/offshore target detection, and imaging radar (e.g., SAR) processing chains. The sea surface under typical sea conditions is not random fluctuation of a single scale, but often presents a multi-scale structure from subtle roughness of a sub-wavelength level to fluctuation of a wavelength level to large-scale waveform of a pixel level, and meanwhile, is driven by a wind field and gravitational waves together, has obvious time evolution characteristics, causes scattering phase to change along with time, and further causes phase center migration. The combination characteristics of multi-scale coupling, large fluctuation and dynamic property ensure that sea surface scattering is influenced by geometric forms and combined action of propagation paths, coherent superposition and motion modulation, and higher requirements are provided for high-precision scattering modeling. In the existing research, modeling methods aiming at rough sea electromagnetic scattering are rich, and common routes comprise approximate deterministic methods such as Geometric Optics (GO), physical Optics (PO) and the like, and numerical solving methods based on integral equations and the like. Research on three-dimensional complex rough sea surface scattering modeling shows that when sea surface morphology is complex and scale span is large, a single approximation model is difficult to consider different scale scattering mechanisms in a unified framework, on one hand, large scale fluctuation has a remarkable influence on local incidence angle and visibility, on the other hand, small scale roughness (especially components related to Bragg scattering) has a key contribution on scattering intensity and polarization response, and if only single scale representation is adopted or coherent consistent connection is lacking among different scales, the problem that multi-scale coherence is difficult to maintain easily occurs, so that the reliability and comparability of the whole scattering field are influenced. In addition to the multi-scale problem, dynamic errors are one of the prominent drawbacks of the prior art. Many modeling and simulation works in engineering applications still practice with static sea surface approximation or quasi-static processing, i.e. generating sea surface morphology at a single moment and performing scattering calculations, and then stitching the time series in some way. However, it has been pointed out in the literature that dynamic sea surface scene modeling based on a dual-scale sea spectrum emphasizes the importance of sea surface evolution over time, and that static approximation is difficult to accurately describe continuous changes in scattering phase over time, and particularly difficult to reflect the effect of phase center migration over time on imaging processing (e.g., SAR focusing). In an application scenario requiring the utilization of phase information, coherent addition information or Doppler modulation information, if dynamic modeling is insufficient, phase error accumulation or coherence reduction is often caused, so that a scattering simulation result is not matched with actual observation in an imaging/detection link. Meanwhile, when a high-precision numerical solution is pursued, contradiction between the efficiency and precision of propagation calculation and green function solution also exists for a long time. The integral equation method or the green function-based solving framework has stronger theoretical completeness, but often faces the problem of huge calculation under the conditions of large-size sea surface, dense dispersion and large fluctuation rough surface, so a rapid algorithm or approximate acceleration strategy is often introduced in engineering. Related studies involve fast solutions of different green's functions (e.g. fast multipole thinking) to improve efficiency, but in complex rough surfaces, especially in large heave conditions, the approximation process may introduce non-negligible errors, resulting in difficulty in obtaining high-precision numerical solutions or the need for significant sacrifice between precision and speed. Therefore, in the prior art, under the common conditions of large range, strong roughness and strong dynamics, coherent maintenance, dynamic consistency and high-precision propagation solution are still difficult to realize at the same time. In recent years, there have also been scholars who propose multi-scale or hybrid schemes to alleviate the limitations of a single model in complex sea conditions and introduce