基于海浪信息的X波段合成孔径雷达台风风速提取研究

Typhoon can affect the heat, water vapour and material exchange between the ocean and the atmosphere, which is the important dynamic process of the oceanographic study. Typhoon wind speed is the basic parameter of typhoon. Obtaining accurate and high precision typhoon wind field can effectively promote the related research of typhoon process. Space-borne synthetic aperture radar (SAR) can obtain high spatial resolution sea surface information in large area following its orbit, which is an important, direct and effective technical way to obtain marine data. Geophysical Model Function is widely used for SAR wind retrieval at present and researches reveal that the error of retrieval wind speed from SAR is about 2m/s as wind speed at low to moderate winds (<20m/s).However, Geophysical Model Function SAR cannot be applied to retrieve strong sea surface wind speed due to backscattering signature saturates under hurricane and typhoon condition (>25m/s). We propose this project, which is based on the characteristics of wind-sea spectrum that containing information of local wind in typhoons. After taking advantage of X-band SAR digital spectrum and employing the recent achievement of the parametric relationship between parameters of typhoon waves and wind speed, sea surface wind speed retrieval from X-band SAR in typhoons can be effectively retrieved. Our research, not only put forward a new method to extract the wind speed in hurricanes and typhoons but also verify its effectiveness, and to make up for the gap of monitoring in hurricanes and typhoons from X-band SAR.

台风可以影响海洋与大气之间的热量、水汽以及物质交换，是海洋学重要研究的动力过程。台风风速是台风的基本参数，获取准确、高精度的台风风场，可以有效的推动台风过程的相关研究。星载合成孔径雷达(SAR)可以在其运行轨道上获得大面积、高空间分辨率的海面信息，是获取海洋数据的重要的、直接有效的技术手段。如今，地球物理模型已被广泛应用于SAR风速反演，研究表明中低风速下(<20m/s)风速的反演误差为2m/s。然而，高风速下(>25m/s)SAR雷达后向散射截面趋于饱和，因此，地球物理模型并不适用于台风情况下的海面风速反演。本课题基于台风浪的海浪谱包含局地风信息的特征，通过使用X波段SAR图像谱，结合最新的研究成果：台风浪要素与风速的参数化关系，从而获得台风风速。本课题的研究，提出了X波段SAR提取台风风速的方法，并通过实例验证其有效性，弥补X波段SAR在监测台风方面的薄弱环节。

在本研究中，提出了一种从合成孔径雷达(SAR)图像中获取极端天气条件下的风速的方法。这种方法的基本原理是基于这样一个事实，即尽管同极化通道在20m/s风速时呈现饱和，但可以成功地利用海浪信息来反演极端天气条件下的风速。因此，本研究利用风-浪之间的参数化关系，即海面风速、有效波高和峰值波期，来反演热带气旋条件下的风速。该方法在TerraSAR-X (TS-X) SAR图像上进行的应用，三个热带气旋(台风Megi、飓风Sandy和飓风Miriam)的反演结果验证了所提出方法的适用性：当将反演的风速与美国国家海洋和大气管理局(NOAA)飓风研究部(HRD)提供的产品的值进行比较时，其均方根误差(RMSE)为2.54m/s。本课题的研究，不仅提出 SAR 反演台风风速方法的可能性并验证其有效性，特别是弥补 X 波段 SAR 监测台风方面的短板。