海面雷达散射及其杂波幅度统计特性的空间遍历性数值仿真研究

Numerical investigation on the spatial ergodicity of ocean radar scattering and sea clutter amplitude statistical characteristics

海面雷达散射的空间遍历性是开展海面散射数值仿真以及分析不同体制雷达系统在海洋遥感应用中算法适用性的重要基础之一。针对随机粗糙海面雷达散射及其杂波幅度统计特性的空间遍历性问题,基于Monte Carlo方法构建包含全部大尺度波浪的粗糙海面模型,利用高精度的全波数值(multilevel steepest decent-sparse matrix canonical grid,MLSD-SMCG)方法以及二阶小斜率近似(2nd-order small slope approximation,SSA-2)模型,分别对不同雷达照射尺寸的一维和二维粗糙海面L波段归一化雷达散射系数及海杂波进行仿真,并对海面雷达散射和海杂波幅度分布的空间遍历性进行分析。仿真结果表明:在无海面遮挡效应的雷达入射和散射角度范围内,雷达照射尺寸大于16λ(入射波波长)粗糙海面的同极化归一化雷达散射系数,具有良好的空间遍历性;当雷达照射海面尺寸不小于对应海况下最大风浪尺度的25%时,海面交叉极化的归一化雷达后向散射系数也表现出空间遍历性。相比海面散射的归一化雷达散射系数,单站海杂波幅度分布在高海况条件下空间遍历性减弱。同极化海杂波幅度分布随着入射角增大,表现出更显著的空间遍历性,而交叉极化情况则相反。

The spatial ergodicity of sea surface radar scattering is one of the important foundations for conducting numerical simulations of sea surface scattering and analyzing the applicability of algorithms for different radar systems in ocean remote sensing applications.This paper numerically investigates the spatial ergodicity of radar scattering from randomly rough ocean surface and its clutter amplitude statistical characteristics.The rough sea surface models including all large-scale waves are firstly generated using the Monte Carlo method.Then,based on the accurate full-wave multilevel steepest decent-sparse matrix canonical grid(MLSD-SMCG)method and 2nd-order small slope approximation model(SSA-2),we simulate the L-band normalized radar scattering coefficients and sea clutters from one-dimensional and two-dimensional rough ocean surfaces with different radar illumination sizes.According to the simulation results,it is found that for radar incidence and scattering angle beyond the range of shading effect,the normalized and polarization radar scattering coefficient from rough ocean surface with radar illumination size larger than 16λ(incident wavelength)has good spatial ergodicity.Also,the normalized radar backscattering coefficient for cross polarization of sea surface shows spatial ergodicity when the sea surface size illuminated by radar is not less than one fourth of the largest wind wave length under the corresponding sea conditions.Comparing to the normalized radar scattering coefficient,the spatial ergodicity of monostatic sea clutter amplitude distribution is relatively weaker under the high sea states.With the incident angle increasing,the amplitude distribution of co-polarized sea clutter shows more significant spatial ergodicity,while the cross polarization case is on the opposite.