NOAA high resolution sea surface winds data from Synthetic Aperture Radar (SAR) on the Sentinel-1A satellite, from 2016-11-01 to 2016-11-30 (NCEI Accession 0157134)

This data set consists of high resolution sea surface winds data produced from Synthetic Aperture Radar (SAR) on-board Sentinel-1A satellite. This product utilizes the CoastWatch product format and the basic archive file is a NetCDF-4 file containing SAR wind, a land mask, and time and earth location information. Also archived will be maps of the SAR wind in GeoTIFF format. The product covers the geographic extent of the SAR image frame from which it was derived. These SAR-derived high resolution wind products are calculated from high resolution SAR images of normalized radar cross section (NRCS) of the Earth's surface. Backscattered microwave radar returns from the ocean surface are strongly dependent on wind speed and direction. When no wind is present, the surface of the water is smooth, almost glass-like. Radar energy will largely be reflected away and the radar cross section will be low. As the wind begins to blow, the surface roughens and surface waves begin to develop. As the wind continues to blow more strongly, the amplitude of the wave increases, thus, roughening the surface more. As the surface roughness increases, more energy is backscattered and NRCS increases. Moreover, careful examination of the wind-generated waves reveals that these surface wave crests are generally aligned perpendicular to the prevailing wind direction, suggesting a dependence of backscatter on the relative direction between the incident radar energy and the wind direction.

本数据集由搭载于哨兵-1A（Sentinel-1A）卫星的合成孔径雷达（Synthetic Aperture Radar，SAR）所生成的高分辨率海面风场数据构成。该产品采用CoastWatch产品格式，基础归档文件为NetCDF-4格式文件，其中包含SAR风场数据、陆地掩膜数据以及时间与地球位置信息。归档内容中还将包含GeoTIFF格式的SAR风场地图。本产品的覆盖范围与其源SAR图像帧的地理范围完全一致。此类通过SAR反演得到的高分辨率风场产品，基于地球表面归一化雷达散射截面（Normalized Radar Cross Section, NRCS）的高分辨率SAR图像计算得出。海洋表面的后向散射微波雷达回波强度与风速和风向高度相关：当无风力作用时，海面光滑如镜，雷达能量将被大量反射，雷达散射截面数值较低；随着风力增强，海面逐渐变得粗糙，表面波浪开始形成；当风速进一步提升时，波浪振幅增大，海面粗糙度进一步加剧；随着海面粗糙度提升，更多雷达能量被后向散射，归一化雷达散射截面随之升高。此外，对风力催生的波浪进行细致观测可发现，这些表面波峰通常与主导风向垂直，这表明后向散射强度与入射雷达能量和风向的相对方向存在显著关联。