面向青藏高原复杂冻土环境的时序InSAR冻土活动层厚度反演研究

As the third pole of the earth, the Qinghai-Tibet Plateau (QTP) has the largest high-altitude frozen region, and the change of active layer thickness (ALT) is closely related with the local or even global climate change. Due to its capacity of all-weather, all-time, large scale coverage and high monitoring accuracy, the applications of Interferometric Synthetic Aperture Radar (InSAR) technique in ground deformation monitoring of QTP permafrost region have gain great attentions. However, due to the dramatic interannual climate change and complicated frozen soil freeze-thaw process in QTP, the InSAR methods for deformation monitoring and ALT retrieval in QTP area are limited by serious decorrelation and inappropriate deformation model. Therefore, this project will retrieve the ALT in complicated permafrost environment of QTP using time-series InSAR. Firstly, the scattering characteristic of the typical features in QTP region will be analyzed and a decorrelation model suitable for the permafrost environment will be proposed. Then, time-series InSAR for permafrost deformation monitoring and the deformation model combining the effects of internal freeze-thaw process and external environmental factor will be development. Afterwards, an ALT retrieval model based on ground subsidence derived from InSAR, land cover types and ground water information will be established. The project will contribute to improving the theories and the information extraction capacity in plateau areas of InSAR technique. In addition, the deliverable of the project will beneficial for development of Tibetan region, safety operation of Qinghai-Tibet Railway, and regional climate change.

作为地球的第三极，青藏高原拥有地球上面积最大的高海拔冻土，其活动层厚度的变化关系到区域乃至全球的气候变化。雷达干涉测量（InSAR）以其全天时、全天候、宽覆盖、高精度等优势，近来在青藏高原冻土信息提取应用中备受关注。由于青藏高原气候变化剧烈、冻土冻融过程复杂，现有InSAR方法在冻土活动层厚度反演中存在着失相干严重、形变模型不合适等问题亟待解决。为此，本项目开展面向青藏高原复杂冻土环境的时序InSAR冻土活动层厚度估计研究。首先研究复杂冻土环境下地物散射特性，构建适合高原冻土环境的失相干模型；然后建立顾及冻融过程和外部因素的形变模型，精确提取冻土形变信息；最后在此基础上，提出综合多因素的活动层厚度反演模型。本项目的开展有助于发展InSAR技术的理论方法，提升InSAR技术在高原冻土区的地表信息获取能力，将为高原寒区建设、青藏铁路安全运营、区域气候变化等提供科学服务。

青藏高原分布着世界上面积最大的高海拔冻土区。随着全球气候变暖的影响，青藏高原冻土正经历着严重的退化，主要表现为冻土温度升高、活动层厚度增大、永冻层厚度减小等，因此对青藏高原冻土进行监测具有重要意义。本项目，以青藏高原多年冻土为研究对象，开展面向青藏高原复杂冻土环境的时序InSAR冻土活动层厚度估计研究，重点突破适合冻土环境的形变模型、冻土参数反演模型，实现复杂冻土环境的冻土形变和活动层厚度的准确估计。通过2019-2021三年的研究，取得的研究成果如下：1）对青藏高原北麓河地区典型地物的在高分辨SAR图像相干性进行分析，探索其季节性变化规律，为时间序列InSAR在青藏高原中的应用中干涉对的选取提供依据；2）提出了一种结合冻融指数和融化指数的冻土形变模型，并成功应用于北麓河、五道梁盐湖地区及冻土工程走廊内冻土地表形变监测中；3）结合InSAR反演的形变信息，提出了一种考虑不同土壤类型的冻土活动层厚度反演模型，并应用于青藏高原北麓河、祁连山等地区；4）培养硕士生2名；发表了论文11篇，其中SCI论文5篇；合著专著1部。通过本项目的研究，提升雷达遥感技术在高原地区的地表信息获取能力，服务于寒区的建设。