海面高阶散射分量受海洋内波调制的机理研究

SSynthetic aperture radar (SAR) images have the potential to observe ocean internal waves and retrieve the internal wave parameters, which are based on the scattering mechanism of ocean internal waves. The measured radar signals modulated by ocean interval waves are larger than the theoretical ones according to the evidence of CoastWatch-95 and SCSE experiment， because the ocean surface statistics can be hypothesized to be the Gaussian distribution in the art-of-state internal waves scattering theortetical model. However, many experiments in the ocean and wind-wave tank have proved that the real ocean surface is always nonlinear, which means that the ocean height and slopes don't submit to Gaussian distribution and their high-order statistics can't be assumed to zero. IEM scattering model can characterize the scatter from the non-Gaussian ocean surface, in which the high-order scattering component can be considered. The point of the thesis is the scatter mechanism of ocean internal waves considering the scattering of nonlinear sea surface, in other words, the scattering from high-order statistics. The thesis is utilized to solve the disagreement between theoretical and measured modulation coefficients in CoastWatch-95 and SCSE experiment. In this thesis, the modulation transfer functions（MTFs）of high-order scattering components caused by internal waves would be established theoretically and MTFs would also be analyzed in the simulation under different radar parameters and wind field conditions. Finally the theoretical MTFs would be compared with the measured ones in experiments. In summary, the new idea is provided by the thesis for the research of the interaction between the internal waves and the electromagnetic waves.

合成孔径雷达（SAR）探测海洋内波和反演内波参数的基础是内波散射机理。国外CoastWacth-95和SCSE海试实验中实测雷达信号受内波的调制系数往往大于理论模型估算值，这是因为内波散射理论模型是基于海面波高服从高斯分布的假设。但是，大量的海试观测和水槽实验已经证明真实海面是非线性的，海面波高并非严格遵从高斯分布，即波高的高阶统计量不能近似为零。IEM散射模型考虑海面波高的高阶统计量下，对非高斯分布海面的散射特性建模。本项目受此启发，在研究内波散射机理时突破海面服从高斯分布的近似，探寻非线性海面下内波的散射特性，从散射机理角度解释海试实测与经典模型的不一致现象。主要工作建立海面高阶散射分量受内波调制的调制传递函数，通过仿真分析不同雷达参数和海况下调制传递函数的特性，并与公开发表的海事试验结果比较。本项目将为认识海洋内波和电磁波相互作用这一科学命题提供新思路。

合成孔径雷达（SAR）探测海洋内波和反演内波参数的基础是内波散射机理。经典内波散射理论是基于海面波高服从高斯分布的假设，但是，国外CoastWacth-95和SCSE海试实验中实测雷达信号受内波的调制系数往往大于理论模型估算值。大量的海试观测和水槽实验已经证明真实海面是非线性的，海面波高并非严格遵从高斯分布，即波高的高阶统计量不能近似为零。IEM散射模型考虑海面波高的高阶统计量下，对非高斯分布的海面散射特性建模。本项目受此启发，在研究内波散射机理时突破海面服从高斯分布的近似，探寻非线性海面下内波的散射特性，从散射机理角度解释实测调制系数与经典模型的不一致现象。.申请人在自然基金委的资助下，开展了海洋内波散射理论和试验研究工作。主要形成研究结果如下：.（1）完成了海面高阶统计量的散射模型研究，推导了考虑海面三阶统计量的海面散射系数表达式，该模型可较好解释顺风和逆风观测时海面散射系数的不一致。.（2）基于该散射模型，建立海面高阶散射量受内波调制的调制传递函数，通过与温度分层水槽试验数据结果比较发现，考虑海面高阶散射量的调制传递函数与实测内波调制系数方面，吻合程度好于原有模型，这点对于Ka波段雷达或者较高风速时尤为明显。.（3）通过海面散射受流场调制特性的水槽试验数据的多普勒分析，发现风速愈大，多普勒谱的双峰现象愈明显，一部分来自于海面二阶散射分量，一部分来自于海面高阶散射分量，而且两部分散射分量受流场调制特性不同。.（4）对水槽试验数据的微多普勒谱分析，进而发现海面二阶散射分量（自由波）的调制机理符合传统波流调制模型，随着雷达波长变短以及海面风速增大，调制系数降低。海面三阶散射分量（受限波）“受限”于长波破碎波一致（在水槽中大尺度破碎波就是其主波），其调制特性与长波保持一致，在中等风速下，海面高阶散射分量（受限波）的调制系数大于海面二阶散射分量（自由波）的调制系数。.本项目将为认识海洋内波和电磁波相互作用这一科学命题提供新思路，也为星/机载SAR图像反演海洋内波参数，以及星载SAR探测尾流载荷分析奠定理论论据。