基于干涉测高模式的波形模拟、重跟踪与相位刈幅处理的水位精提取

The development of a new generation interferometry altimetry satellite will be incorporated in the 14th National Five-Year Plan on schedule. In this proposal, we take the currently only interferometric altimeter satellite, Cryosat-2, as the research object, and perform the study of accurate water extraction based on the improvement of interferometric waveform and phase processing. Compared with pulse-limited altimetry satellites, Cryosat-2 mission passes many lakes in the so-called SAR interferometry (SARin) mode at improved along-track resolution. Still, the accuracy and robustness of standard level 2 is limited due to pollution of the waveform by surrounding land topography. Fortunately, Cryosat-2 has very unique waveform characteristics, the waveform signals from land surfaces and water surface are visible as several distinguishable peaks.Based on the basic interference principle of Cryosat-2's altimeter, we firstly perform the simulation of return waveform , then propose to actively extract the water surface component by a novel retracking method based on cross-correlation of observed level 1b waveforms with a generic simulated waveform. Preliminary experiments show that the return path delay should consider the factors including satellite horizontal and vertical velocities and the displacement during the period of pulse transmit-receive. If the return power of observed level 1b waveform is very weak, the swath processing of the corresponding differential phase can be overcome the poor accuracy of waveform retracking. The smooth implementation of this project will provide the reference and support for the future data processing of altimetry satellite in our country.

发展新一代干涉测高卫星按计划将列入国家十四五规划，本项目以目前世界上唯一一颗具有干涉模式的测高卫星Cryosat-2为对象，开展基于干涉波形与相位处理的水位精提取研究。相较传统脉冲有限式高度计，Cryosat-2能够以更高沿轨分辨率对陆地水进行监测，然而它的回波受到周围地形的污染，导致标准的Level-2产品精度降低，有效数据受到限制。幸运地是，Cryosat-2的回波具有多个可分辨的尖峰状波峰这样独特的波形特征。我们首先从Cryosat-2高度计基本干涉原理出发，对湖面干涉波形进行模拟。预实验表明，回波路径延迟应当考虑卫星水平速率、垂直速率以及脉冲收发期间的位移。然后基于模拟的干涉波形与卫星观测波形的互相关关系，高精度提取水面高程。如若回波功率很弱，通过干涉相位的刈幅处理弥补波形重跟踪水位提取的不足，本项目的顺利实施将为我国未来干涉测高卫星的数据处理提供借鉴与支持。

测高卫星使用在探测水位变化上具有其他手段无法比拟的技术优势，但由于受陆地地形及杂波的影响，Cryosat Level 2级产品的数据质量在内陆区域受到损失，甚至在卫星过境的某些区域上出现数据缺失。本项目基于观测波形(observed Level 1b waveforms)与模拟类波形(generic simulated waveform)的互相关关系，提出了一种新的卫星高度计回波波形重跟踪算法，利用该算法能够精确提取受陆地噪声污染的水位。同时，借助奇异谱分析技术，对重跟踪前后的高度计水位序列的噪声水平进行评估，并利用GRLM数据定量评估新方法的改进效率。同时，我们对影响精度的海况偏差进行了改正。