CryoSat-2 SARIn数据干涉处理及DEM获取

CryoSat-2 SARIn Interferometric Processing for DEM Generation

CryoSat-2搭载的合成孔径/干涉雷达高度计能够精确地探测海洋与大陆冰面高程变化,其合成孔径干涉模式(synthetic aperture interferometric mode,SARIn)提供的干涉数据可以利用传统差分干涉测量技术反演地面的高程信息,但在欧洲空间局公布的SARIn二级产品没有充分地利用这一信息。介绍了SARIn模式工作原理,并结合传统干涉测量技术,提出利用SARIn一级(level 1b,L1b)数据进行数字高程模型提取的算法和流程。通过数据质量检查,剔除数据中的错误信息;通过信号强度和相干性选择合适的解缠起点,实现干涉数据的逐行解缠;计算出卫星视角,结合卫星姿态、速度、位置和视线向距离等信息计算地面点的三维信息,最终插值生成SARIn DEM(digital elevation model)。利用该算法对2012年1月~4月的SARIn L1b数据进行干涉处理,获得了南极Lambert冰川流域局部地区的数字高程模型。通过对比ICESat DEM和RMAP DEM,表明SARIn DEM具有较高的精度,能够满足南北极等地区的高程变化研究。

The SAR/interferometric radar altimeter （SIARL） on the CryoSat-2 platform is designed to accurately determine the height changes in the Earth＇s continental and marine ice fields. In addition, its synthetic aperture radar interferometry mode （SARIn） is capable of providing precise three-dimensional measurements. However, SARIn level 2 products provided by the European Space Agency （ESA） do not fully utilize interferometric information. In this paper, the basic principles of the SARIn mode are introduced. By integrating the traditional interferometric synthetic aperture radar （InSAR） technique, a processing scheme is proposed for SARIn level 1b （L1b） data to extract digital elevation models （DEMs）. This processing scheme uncludes three steps. Firstly, checking the quality of the input data eliminates erroneous information. Secondly, a starting point for phase unwrapping is determined, based on the magnitude and the coherence of the received signals and a targeted algorithm is accirdingly designed and implemented to unwrap the interferometric phase along the across-track direction on a line-by-line basis. Thirdly, the look angle of the satellite is calculated and used to estimate the 3D information of ground points. After a process of interpolation, DEM are generated. With the use of the proposed scheme, the SARIn L1b data acquired between January 2012 and April 2012 were processed. The ground elevation of Lambert Glacier in Antarctic was mapped and compared to the ICESat DEM and RAMP DEM. The results demonstrate that a DEM generated based on SARIn data can satisfy the research requirements for ice cap mapping in polar areas.