无雨和有雨情况下海面小入射角电磁散射特性的仿真研究

Sensors working at low incidence angles have become a hotspot in ocean microwave remote sensing. This makes electromagnetic scattering characteristics of the sea surface at low incidence angles very important, because the relationship between them and relative factors directly decides the effects by the factors on echo singles received by the sensors, which are primary data in retrieval procedure of remote sensing. However, remote sensing data sources of ocean in microwave region at low incidence angles are very limited, and cannot provide diversity and comprehensiveness. Thus, the scattering characteristics are studied by means of simulation in this research project. Approximate analytical method and numerical method will be used to build simulation model of electromagnetic scattering from the sea surface. By dielectric constant model of sea water, ocean wave spectrum, spectrum of ring waves induced by rain and radiative transfer theory, the factors (e.g., sea water temperature, salinity, winds, water depth, rain, etc.) will be coupled in the simulation model. Compared with experiment, an advantage of simulation is that the factors can be modified flexibly. Based on the simulation model, the change law of the scattering characteristics with respective to the factors will be explored, and the effects of rain-induced turbulence on the sea surface and single- and multiple-scattering of rain droplets will also be studied. This project is novel, and has important scientific significance in both contents and methodology. It will also provide valuable reference in interpretation and analysis of remote sensing data of the future on-orbit ocean microwave sensors working low incidence angles, which are currently under development in our country.

小入射角传感器正逐渐成为海洋微波遥感领域的热点，使得海面的小入射角电磁散射特性变得十分重要，它与相关因素的变化关系直接决定了这些因素对传感器（赖以进行遥感反演的）接收信号的影响。但是目前小入射角海洋微波遥感的实测数据源非常少，难以保证数据多样性和全面性。因此本项目提出通过仿真来展开研究。本项目拟采用近似解析方法和数值方法来建立海面电磁散射仿真模型，并通过海水介电常数模型、海浪谱、降雨环形波纹谱及辐射传输理论，将海水温盐、风场、水深及降雨等因素耦合到模型中。相比实验手段，仿真手段优势在于参数灵活可调。本项目基于仿真模型进一步探索海面小入射角电磁散射特性关于上述因素的变化规律，研究降雨扰动海面以及雨滴单重散射和多重散射对该散射特性的影响。本研究侧重基础性，选题新颖且在研究内容和方法手段上都具有重要的科学意义；对我国正在研制的小入射角海洋微波传感器在轨后的遥感数据解译分析也具有重要的参考价值。

本项目基于近似解析方法、数值方法以及辐射传输理论，开展了无雨和有雨情况下海面小入射角电磁散射特性的仿真研究。本项目首先结合多种近似解析方法（包括几何光学法、微扰法及积分方程法）和海浪谱，建立了海面小入射角电磁散射近似解析模型，同时结合物理光学法和基于海浪谱的蒙特卡洛海面模拟，建立了海面小入射角电磁散射数值模型。基于上述近似解析模型和数值模型，本项目仿真分析了无雨情况下海面风场、海表温盐、电磁波频率等因素对海面小入射角电磁散射特性的影响。此外，降雨引起的环形波会影响海面粗糙度，同时雨层会衰减和散射电磁波。因此，本项目结合近似解析方法和辐射传输理论，构建了降雨情况下海面小入射角电磁散射模型。基于模型，本项目仿真分析了降雨的各种效应对海面小入射角电磁散射特性的影响。本项目的仿真结果可为进一步深入探索小入射角下海面电磁散射的复杂机理提供参考。