Hwang Paul A, Ainsworth Thomas L, Ouellette Jeffrey D
Remote Sensing Division, U.S. Naval Research Laboratory, Washington, DC 20375, USA.
Sensors (Basel). 2021 Feb 20;21(4):1486. doi: 10.3390/s21041486.
Microwave reflectometers provide spectrally integrated information of ocean surface waves several times longer than the incident electromagnetic (EM) wavelengths. For high wind condition, it is necessary to consider the modification of relative permittivity by air in foam and whitecaps produced by wave breaking. This paper describes the application of these considerations to microwave specular returns from the ocean surface. Measurements from Ku and Ka band altimeters and L band reflectometers are used for illustration. The modeling yields a straightforward integration of a closed-form expression connecting the observed specular normalized radar cross section (NRCS) to the surface wave statistical and geometric properties. It remains a challenge to acquire sufficient number of high-wind collocated and simultaneous reference measurements for algorithm development or validation and verification effort. Solutions from accurate forward computation can supplement the sparse high wind databases. Modeled specular NRCSs are provided for L, C, X, Ku, and Ka bands with wind speeds up to 99 m/s.
微波反射计能提供海面波谱积分信息，其波长比入射电磁（EM）波波长长得多。在强风条件下，有必要考虑泡沫和破浪产生的白帽中空气对相对介电常数的修正。本文描述了这些考虑因素在海面微波镜面反射中的应用。以Ku和Ka波段高度计以及L波段反射计的测量结果为例进行说明。该模型直接整合了一个封闭形式的表达式，将观测到的镜面归一化雷达散射截面（NRCS）与表面波的统计和几何特性联系起来。获取足够数量的用于算法开发或验证及确认工作的强风并置同步参考测量数据仍然是一项挑战。精确的正向计算解决方案可以补充稀疏的强风数据库。给出了风速高达99米/秒时L、C、X、Ku和Ka波段的模拟镜面NRCS。
