粗糙表面模型及其电磁散射特性的卫星雷达高度计海况偏差研究

The project will study the current main problem: the satellite radar altimeter (altimeter) measures the sea surface height with several centimeter precision(less than 5cm) and the current sea state bias with 2cm error becomes the main source of measuring high error. because the theoretical research of the sea state bias is complex and the final results are difficult to apply in practices, the Empirical research has become the main research direction of sea state bias and its correction. however, the Empirical research involves a large amount of data but does not involve physical mechanism, and also the researched results are limited by the local sea conditions at that time. Therefore, this project is expected to use electromagnetic field theory and numerical calculation method to study sea state bias from the physical mechanism and cause of sea state bias. Specifically: (1) a two and multilayer-medium-rough sea surface model is established and the electromagnetic scattering coefficient and the scattering power of the established model are computed and studied by the electromagnetic field numerical method. (2)the corresponding average sea level of the model, the average scattering surface and the median scattering surface and their differences are studied in order to study the sea state bias. (3) Simulating the returns from the model which received by the altimeter and retrieving oceanic parameters (wind speed, significant wave height and backscatter coefficient)from the returns. The look-up table and the Least square fitting with having oceanic parameters will be presented. (4)the correction of sea state bias will be verified and studied. The research results of this project are expected to be used in sea state bias correction of altimeter, and also provide basis and data support for theoretical understanding of sea state bias.

研究当前一个主要问题：卫星雷达高度计(称高度计)以几个厘米(5cm)精度对海面高度进行测量，而海况偏差就有2cm，成为高度计测高误差主要来源。由于海况偏差的理论研究比较复杂且所得结果难于应用，所以经验研究成为海况偏差及其校正主要研究方向。然而经验研究数据量大和未涉及物理机理，而且研究结果受限于当前海况，校正精度提高困难。因此，本项目预计从海况偏差物理机制和成因出发，运用电磁场理论和数值计算方法来研究。具体地：(1)建立二层、多层介质粗糙海面模型，运用电磁场数值计算方法计算模型整体、局部电磁散射散射系数和功率。(2)研究平均海平面、平均散射面、中值散射面之间差值来研究海况偏差。(3)模拟高度计接收模型回波并反演海洋参数(风速、有效波高及后向散射系数)，提出与海洋参数相关的海况偏差查找表、最小二乘拟合式。(4)对海况偏差校正方法验证研究。研究结果用于高度计海况偏差物理机制理解和应用到实践中。

按申请书计划执行。完成了基于粗糙海面电磁散射特性的海况偏差研究。(1)主要完成了多种分布海谱模拟的粗糙海面建模及其电磁偏差模拟计算：平均海平面高度，平均散射面和中值散射面高度。计算了多种不同海谱分布的粗糙海面的电磁偏差、倾斜偏差及海况偏差，揭示了偏态(非线性)分布海谱的海面存在海况偏差的物理原因。(2)得到了关于有效波高和风速为参数的海况偏差查找表(最小二乘表达式)，用于对海况偏差校正。下载了HY2数据对海况偏差校正模型进行验证。(3)本项目突破与创新：提出了含偏斜系数和电磁偏差系数的二阶反演模型，进而提出五参数反演模型，反演偏斜系数，在弱非线性效应下，反演电磁偏差和倾斜偏差及海况偏差，理解了海况偏差物理原理和得到海况偏差全球季节性分布特性。(4)浮标数据做参考，下载中法海洋卫星波谱仪天底点数据和HY2高度计数据进行反演有效波高进行验证，利用本项目提出的反演算法反演有效波高精度比传统的、当今业务算法高，结论基本正确，有望在未来高度计波形重跟踪中运用。