基于L波段主被动微波遥感观测的地表冻融状态监测算法研究

Landscape freeze/thaw is the most unique process as it is associated with water transitioning between solid and liquid phases. The global mapping of freeze/thaw state is scientifically important to understanding land surface hydrological processes and the global water cycle. Currently, there are several issues regarding to microwave remote sensing of soil freeze/thaw including less developed model, non-sufficient criterions, and the weak ability of the synergy between passive and active microwave remote sensing. Thus, this project will focus on the study of microwave radiation and scattering mechanism of soil freezing and thawing process. The soil would be treated as plane stratified dielectric layers to consider the effects of different soil temperature and moisture gradients. Ground-based observations of active and passive signals will be conducted by using a RPG-DP-6CH radiometer and the cGB-SAR radar. The best criterions will be evaluated and selected on the basis of simulation and experimental data in order to enhance the applicability of the algorithm. The algorithm is designed to be tested with the Aquarius and SMAP active and passive observations. And extensive ground observations would be used to assess the accuracy and scaling effects of soil freeze/thaw discrimination results with different spatial resolution. This study is a comprehensive utilization of the main advantages of passive and active observations, and will further improve the theoretical foundation of soil freezing and thawing monitoring. It also provides a scientific basis for the demonstration of water-related satellite missions.

地表冻融过程涉及土壤中液态水和固态冰之间的相态交替作用，在众多的地表过程中显得极为独特，其遥感监测对于理解陆面水文过程乃至全球水循环具有重要科学意义。当前微波遥感监测地表冻融研究还存在机理欠完善、判据不充分、协同能力弱等问题，因此本项目将以研究土壤冻融过程的微波辐射散射机理为基础，考虑土壤分层结构下不同温度和水分梯度的影响；针对典型冻融日变化过程开展主被动协同的地面观测试验，并在模拟和试验数据基础上选择最佳判据以增强算法的适用性，从而在机理层面上提高主被动微波遥感的相互配合能力并发展冻融状态监测方法，结合地面网络观测研究不同空间分辨率的冻融判别结果的精度差异和尺度效应，为综合利用主被动观测优势以及进一步提高冻融监测水平提供理论支持，也为我国相关水循环卫星的论证提供科学依据。

地表冻融过程涉及土壤中液态水和固态冰之间的相态交替作用，有效的多源遥感监测对于理解寒区陆面水文过程具有重要科学意义。本研究通过考虑土壤分层结构，加入土壤剖面水分和温度信息构建了地表冻融过程的多波段微波辐射散射机理模型，发现了不同波段的冻土穿透深度差异；通过多波段、多极化信息的组合，发现了能够反映冻融变化特征的新判据，即亮温通道间的相对偏差，改进了判别式算法方程系数以及季节性阈值算法中的归一化方法，有效提升了地表冻融状态判别精度；发展了2002年至今的全球地表冻融状态被动微波遥感数据集，并进一步结合光学和热红外遥感，发展了融合多源遥感观测的地表冻融状态降尺度技术，增强了多源遥感观测的协同能力以及当前冻融状态遥感产品的空间分辨率，为理解全球变化背景下地表冻融循环的变化和响应奠定了技术基础。