海洋锋对海浪SAR成像及海浪要素反演的影响研究

Ocean fronts are familiar in the ocean which characterized by the strong current gradient and different physical character between the surface water of two sides of front area. Ocean fronts affect surface waves by causing refraction and forming different wind speed. Synthetic Aperture Radar (SAR) is a valid instrument which can observe surface waves and ocean fronts simultaneously. The research on SAR ocean observation and SAR wave imaging suggest that the fields of surface waves on the two sides of ocean front in SAR images show different statistical characters due to the modulation of current velocity and SST. However, there is no investigation reported that interpret the effect of ocean current on SAR-wave imaging mechanism and retrieval of wave parameters. In this project, we intend to analyze the SAR images containing both surface waves and fronts combined with the results from the wave and current numerical model, interpret the SAR imaging mechanism of ocean fronts effect on surface waves, assess the degree of modification of modulation transfer function and SAR spectra due to the different current velocity and SST, and provide the correction scheme of the retrieved parameters of surface waves from SAR taking into consideration of the variation of current field and SST gradient. These study will improve the understanding of the SAR-wave imaging mechanism and provide the reliable data resources for systematically investigating wave-current interaction.

海洋锋是一种常见的海洋现象。海洋锋区两侧表层海水具有强流速梯度且具有不同的物理性质，通过产生折射效应和风速差异对海气界面的海浪产生影响。SAR是可以同时观测波浪和海表锋面的有效遥感手段之一。已有的SAR观测和海浪成像研究表明：SAR图像中锋区两侧的海浪场在非均匀流速和SST的调制下表现出不同的特征。然而，尚未有阐述海洋锋对波浪SAR成像及波浪要素提取影响的研究报道。本项目通过分析同时包含锋面和海浪条纹的SAR影像并结合海流海浪联合模式后报结果，阐明锋面对波浪在SAR上成像的影响机制，估计不同流速和SST对调制传递函数和SAR谱的影响程度，提出在考虑强流切变和SST梯度情况下海浪要素反演结果的修正关系。该工作为深入理解SAR的海浪成像机理奠定基础，为系统研究海洋锋附近波-流相互作用提供可靠的数据来源，为SAR数据进行准确的海浪要素反演提供技术保证。

合成孔径雷达（SAR）是可以同时观测波浪和海表锋面的微波成像雷达。目前海洋锋面对SAR信号的调制以及如何合理地反演锋面区域的海洋动力环境参数是微波海洋遥感领域的一个基础问题。项目旨在研究SST和非均匀流场影响SAR海浪成像的机制，发展中国近海SAR影像海浪反演模式。通过四年的研究，项目组成员较好地完成了预定的科研任务。研究表明，约有60%的锋面样本SST高的一侧后向散射截面值高，约有70%的锋面SAR图像样本海表面风速高的一侧后向散射截面高。锋面两侧后向散射截面的差异随平均SST的增大而增大，并与海表面风速的差异成正比。通过全球海浪数据分析，建立了反波龄与涌浪能量占混合浪能量比例（Ws）之间的关系，证明了小的反波龄对应涌浪能量在混合浪能量中所占的比例大。还参考了高频地波雷达的涌浪观测数据与反演方法在近海区域的适应性。基于这些结果，发展了中国近海基于双极化SAR的海面风、浪的反演模式，该成果也已应用于海洋卫星观测业务部门。项目资助发表论文10篇，其中SCI、EI收录8篇。申请专利1项，授权专利3项。研究成果加深了对海面—SAR的成像机理的理解，对完善SAR的海洋定量化应用具有参考意义。