多层粗糙表面介质模型的高海况星载雷达高度计参数反演与校正算法研究

The project mainly investigates the current problem in the following: at high sea states such as tropical cyclones,typhoons,hurricanes and so on, the satellite radar altimeter (referred to as the altimeter) measurement data due to those factors are affected to a great extent and thus the precision of retrieving parameters(significant wave height, sea surface wind speed and sea surface height and etc.) is very poor. Because these high sea staes such as the typhoon, hurricane usually associated with big waves，strong rainfall，and also aroused foams and spray droplets which constitute a whitecap layer on the surface of the sea and increase the surface roughness, will directly affect the altimeter echo waveform, thereby affecting accuracy of inversion parameters. Therefore,the project firstly plans to study the characteristics of electromagnetic wave striking on the air-sea mixed surface by establishing a multilayer randomly rough dielectric model. After comprehensively understanding and calculating the electromagnetic scattering theory in the details the project will put forward an improved relationships with cosidering about the effect of whitecaps between the ku and C band backscattering coefficents to correct the relationships about theirs at the usual sea states. Secondly, after understanding these mechanisms and principles about whitecaps and rainfalls influencing measured data of altimeter and radiometer, the project will study some recycling iteration and corrections to finish correcting significant wave height and backscattering coefficients for reducing the rainfall and whitecaps effect by mainly using HY-2 and typhoons shanshan data, and then correct the sea surface height and wind speed. Finally, the result about these corrections and their application cases, steps and precisions will be presented.

本项目主要研究当前一个问题：在热带气旋、台风和飓风等高海况下，星载雷达高度计(简称高度计)测量的数据受此影响而反演参数(有效波高、海面风速和海面高度)精度较差。由于台风、飓风等高海况通常伴随大浪及强降雨，而且在海面会激起泡沫、飞沫等白冠层，增加海面粗糙度，这些都会影响高度计回波波形，进而影响参数反演精度。所以，本项目首先建立多层随机粗糙表面介质模型来研究海气混合海面电磁散射特性，在详细计算和透彻理解海气混合海面电磁散射特性基础上，通过对Ku、C波段后向散射系数之间关系的修正，提出一种考虑白冠影响的Ku、C波段后向散射系数之间关系。其次，在理解白冠、降雨对高度计测量数据影响机制前提下，研究循环迭代原理和方法，主要就海洋2号、台风珊珊数据，重点考虑降雨、白冠影响，研究校正算法并对后向散射系数、有效波高进行校正，进而对风速和海面高度进行校正。最后，给出高海况下的参数反演及其校正方法、精度及应用。

项目的背景：本项目主要研究当前一个问题：在热带气旋、台风和飓风等高海况下，星载雷达高度计(简称高度计)测量的数据受此影响而反演参数(有效波高、海面风速和海面高度)精度较差。由于台风、飓风等高海况通常伴随大浪及强降雨，而且在海面会激起泡沫、飞沫等白冠层，增加海面粗糙度，这些都会影响高度计回波波形，进而影响参数反演精度。.主要研究内容：(1)完成研究建立多层随机粗糙表面介质模型：空气-飞沫-泡沫-海水多层粗糙表面模型，空气-降雨-海水多层粗糙表面模型，空气-降雨-飞沫-泡沫-海水多层粗糙表面模型。(2)研究数值计算方法时域有限差分法FDTD、钜量法MOM、基尔赫夫近似法KA及多层平行电磁理论来研究多层粗糙表面模型的Ku/C波段电磁散射特性：反射率，后向散射系数，以及降雨和泡沫、飞沫衰减特性。(3)研究Ku、C波段后向散射系数之间关系的及有泡沫、飞沫存在时标准关系的修正，提出一种考虑白冠影响的Ku、C波段后向散射系数之间关系。(4)在理解白沫、降雨对高度计测量数据影响机制前提下，研究循环迭代原理和方法对降雨/白沫(飞沫和泡沫)进行校正, 给出高海况下的参数反演及其校正方法。(5)主要就台风珊珊数据，重点考虑降雨、白沫影响，研究校正算法并对后向散射系数、有效波高进行校正，进而对风速和海面高度进行校正。.重要结果：建立了多层粗糙表面模型及仿真程序和集成软件。FDTD\MOM\KA计算多层平行介质理论方法计算了多层粗糙表面电磁散射特性及程序和集成软件：降雨和飞沫-泡沫对Ku、C波段脉冲的衰减特征，降雨和飞沫-泡沫校正方法和方案。神经网络方法反演大气温度、湿度和液态水含量结果用于大气校正。发表6篇学术论文，一篇发明专利在公示阶段，毕业四名研究生。考虑到后两年预计有两篇学术论文发表，本项目能完成计划。.关键数据：降雨衰减校正表，白沫(泡沫、飞沫)衰减及其引起有效波高变化的校正表。台风姗姗数据校正及大气温湿液态水含量反演数据。.科学意义：校正方法和方案应用到台风姗姗数据校正，神经网络方法应用于地基微波辐射计大气温度湿度液态水含量反演和台风姗姗校正。结果与数据可广泛应用到天气海洋预报、海洋工程、渔业等部门及 海洋动力环境科学研究中。