南黄海辐射沙脊群海域浅海地形SAR成像理论与遥感探测研究

Shallow water topography is one of the key components of coastal ocean environment. Its’ measurement is significant for studying coastal ocean dynamics and plays an important role in coastal navigation, ocean fisheries, offshore engineering, and effective coastal zone management as well as marine military activities. The bathymetry of the radial sand ridge region in the southern Yellow Sea is remarkably complicated and changes rapidly. The project aims to study the theory of SAR (synthetic aperture radar) imaging of along-tidal-current underwater ridges and develop bathymetry assessment model using both satellite SAR imagery and ocean modelling. Firstly, the shallow water SAR imaging theory is explored based on two-dimensional (2D) ocean model and ocean surface microwave backscattering model. Using nearly 100 satellite SAR images and synchronous ocean current and wind data, we will theoretically and statistically investigate the influence of ocean current and wind on SAR imaging of shallow water topography in the study area. The results will not only complement the existing theory of SAR imaging of shallow water topography, but provide technical supports on offshore resource exploration and sustainable development of local environment.

浅海地形是海洋环境的重要要素。探测浅海地形不仅对近海动力学的理论研究具有重要意义，而且对海上交通运输、海洋渔业、近海工程、海岸带开发和利用及海洋军事等均具有重要意义。本研究立足我国地形地貌复杂多变的典型海域-南黄海辐射沙脊群海域，旨在综合利用星载合成孔径雷达（Synthetic Aperture Radar，SAR）和海洋数值模拟开展平行于潮流方向的浅海水下地形的SAR成像理论研究。首先基于二维海洋模型与海面微波散射成像模型，开展浅海地形SAR成像理论研究。结合大量星载SAR影像和同步潮流、海面风数据，从理论与统计分析两个层面探讨潮流与海面风对浅海地形SAR成像的影响。研究成果既是对SAR浅海地形遥感成像理论的有益补充，又可为SAR浅海水深反演提供理论基础，从而近海水域的合理开发和利用以及环境生态的可持续发展提供技术支撑。

项目基于2005～2010年期间获取的近百景具有高空间分辨率（30 m）的ENVISAT ASAR 影像及ERS-2 SAR影像，结合SAR成像时刻的NOAA/NCDC海表面风场数据和海洋数值模式流场数据，以南黄海辐射沙脊群海域为例，开展了潮流与水下地形特征（沙脊、潮道）平行情况下的浅海地形SAR图像特征及成像机制研究。结果表明，对于南黄海辐射沙脊群海域，风速范围在3~9m/s、潮流流速较大以及涨潮时有利于水下地形成像。一个重要的发现是，不同时刻获取的SAR影像显示了两种完全不同的水下地形特征：一类是对应潮道位置的宽亮条纹图像特征，另一类是对应沙脊位置的细亮条纹图像特征。结合平行于水下地形的流场剪切诱发的次级环流理论，项目初步探讨了可能造成这种差别的 SAR浅海地形成像机制：当风引起的Ekman流与潮流场流向相反时，相邻两沙脊之间的潮道上方海面流场会发生辐聚，使得SAR所接收到的海面后向散射能量增强，因此潮道在SAR图像上显示为宽的亮条纹；当风引起的Ekman流与潮流场流向相同时，则会引起相邻两沙脊之间潮道上方海面流场的辐散，这将导致相邻两潮道之间的沙脊上方流场产生辐聚，此时沙脊在SAR图像上显示为细的亮条纹。