Role of surface films in ERS SAR signatures of internal waves on the shelf - 1. Short-period internal waves
Role of surface films in ERS SAR signatures of internal waves on the shelf - 1. Short-period internal waves
复制标题
DOI：
10.1029/97jc02725
复制
发表时间：
1998-04-15
影响因子：
3.6
通讯作者：
Kijashko, SV
中科院分区：
文献类型：
--
作者：
da Silva, JCB;Ermakov, SA;Kijashko, SV
分析合成孔径雷达（SAR）图像的内波（IWs）在伊比利亚大陆架和分类的IW表面签名。有三种类型的IW特征，分别对应于雷达后向散射的正/负、负或正变化的亮/暗、暗和亮带的形式。强正号IW信号出现在非常低的风速（小于2 m/s）。在风速高于2米/秒的正/负和负的签名观察范围传播IWs。对于方位角传播的IWs，负签名占优势。叙述了1994年8月在伊比利亚大陆架上在北大西洋东部多学科海洋学研究项目框架内进行的两组实验：（1）与ERS-1合成孔径雷达立交桥同时进行的IW测量和（2）IW测量、表面目视观测和海面胶片取样。在低到中等风的IW表现形式的浮油位于IW槽的形式，在近阈值风速，他们的形式的加强分米级波（antislicks）位于IW波峰。从光滑和nonslick地区收集的膜的波阻尼线索的测量表明，表面活性剂的浓度和检索膜弹性是在浮油比在nonslick地区。建立了一个表面波调制的理论模型，该模型考虑了表面波在IW电流作用下的应变和表面活性剂薄膜对表面波的阻尼。模型中采用了真实的海洋生物膜的压力-面积曲线。在IW领域的表面波频谱上的薄膜和应变效应之间的关系示出依赖于薄膜参数，表面波长，和风速。该模式预测了厘米级波浪在IW槽上的强阻尼主要是由于薄膜效应，分米级波浪的增强和抑制主要是由于应变和薄膜效应，得到了模式谱变化作为风速的函数的距离和方位传播的IW，负号对比度被示出占主导地位的方位传播的IW。分米尺度波的频谱的模型变化被证明是显着敏感的表面活性剂（膜压力），由于膜被叠加在应变效应的负符号对比，这些最终能够抑制正符号对比。它的结论是，在SAR图像中的不同类别的IW签名的发生可以解释的表面活性膜的作用。
Analysis of synthetic aperture radar (SAR) images of internal waves (IWs) on the Iberian shelf and classification of the IW surface signatures is presented. There are three types of IW signatures in the form of bright/dark, dark, and bright bands that correspond to positive/negative, negative, or positive variations of radar backscatter, respectively. Strong positive sign IW signatures occur at very low wind velocities (less than 2m/s). At winds higher than 2 m/s both positive/negative and negative signatures are observed for range-propagating IWs. For azimuth-propagating IWs, negative signatures prevail. Two groups of experiments carried out in the frame of the Multidisciplinary Oceanographic Research in the Eastern North Atlantic (MORENA) project on the Iberian shelf in August 1994 are described: (1) IW measurements simultaneous with ERS-1 SAR overpasses and (2) IW measurements, visual observations of the surface, and sampling of films from the sea surface. IW manifestations at low to moderate winds took the form of slicks locating over IW troughs; at the near-threshold wind velocity they were of the form of intensified decimeter-scale waves (antislicks) located over IW crests. Measurements of wave damping cue to films collected from the slick and nonslick areas showed the concentration of surfactants and retrieved film elasticity to be higher in the slicks than in the nonslick areas. A theoretical model of the surface wave modulation by IWs is developed to include surface wave straining by the IW current and surface wave damping due to surfactant films. Pressure-area curves for real marine films are used in the model. The relation between the film and the straining effects on the surface wave spectrum in the IW field is shown to depend on film parameters, surface wavelength, and wind velocity. The model predicts strong damping of centimeter-scale waves over IW troughs mainly due to the film effect and intensification and depression of decimeter-scale waves due to both straining and film effects, Dependencies of the model spectrum variations as a function of wind velocity for range and azimuth propagating IWs are obtained, the negative sign contrast being shown to predominate for azimuth propagating IWs. Model variations of the spectrum of decimeter-scale waves are shown to be significantly sensitive to surfactants (film pressure), the negative sign contrasts due to films being superimposed on the straining effects, and these are eventually capable of suppressing the positive sign contrasts. It is concluded that the occurrence of the different classes of IW signatures in the SAR images can be explained by the action of surface-active films.