Permafrost in Qinghai-Tibet Plateau (QTP) has been suffering from global warming in recent years, characterized by the deepening of the permafrost active layer. Seasonal changes in permafrost are usually reflected as ground surface deformation, which can be monitored by multi-temporal interferometric synthetic aperture radar (MT-InSAR) technology. Owing to the extreme environment in the QTP, there are few ground-based deformational observation data available, and records of permafrost monitoring by MT-InSAR with ground validation are limited. Here we present a study of surface deformation monitoring for permafrost with MT-InSAR technology validated by a large number of in-situ observations compared with the previous published results. In this study, a small baseline subset (SBAS) method was used with ENVISAT ASAR data in WuDaoLiang, QTP, to acquire the surface deformation and to analyze the corresponding characteristics. The results were first validated with 24 GNSS leveling observation points along the Qinghai-Tibet Railway, including numeric validation (e.g., statistics and KS test) between the InSAR derived deformation and the time-interpolated GNSS leveling values, and the variation trend of the two deformation sequences during a permafrost deformation period, at each observation point. Considering both the differences in magnitudes and trends, the deformation at 22 out of 24 points detected by InSAR corresponded well to the GNSS observation series over one year, which indicates the reliability of MTInSAR for permafrost monitoring. After validation, the amplitudes and linear velocity of the InSAR deformation in this region were calculated and analyzed, together with selected points in different types of terrain. Generally, in the deformation map, most pixels show a trend of periodic and seasonal displacement, uplift in winter and subsidence in summer, with amplitudes of 3-10 mm in most regions. The deformation in mountain areas is less than that of flat lands in amplitude, and shows more randomness in periodic characteristics. Meanwhile, some points with obvious settlement have been detected, probably corresponding with permafrost degradation.

作为气候变化"指示器"的青藏高原多年冻土,近几十年来受到越来越多学者关注。但是已有冻土区地表形变的研究,多单纯针对地表抬升和沉降量进行分析,鲜有针对不同高寒草地类型进行深入挖掘的。在位于青藏高原多年冻土区腹地的五道梁地区,利用ASAR数据和SBAS-InSAR方法反演了区域内2005年4月到2010年7月的地表形变状况。结果显示研究区地表形变速率基本位于±8 mm/a之间。其中,变形率为正、地表呈现抬升的区域占57.70%,地表形变为负、地表沉降的区域占42.30%。此外,高寒草地整体表现地表下沉的现象,而且高寒草原的地表沉降现象明显强于高寒草甸地区。计算获得3种生态遥感指数后,分析地表形变与生态遥感指数的相关性,发现针对不同草地类型,其地表形变的主导因子存在差异。高寒草甸的地表形变有可能更多的受限于温度变化,而高寒草原的地表形变则可能更多的由水分条件所影响。以上研究说明青藏高原多年冻土区植被类型条件越好,地表沉降量越小。因此今后的相关研究需要对植被类型条件差的区域增加更多的关注,因为这些地区易发生地表沉降,导致其生态系统稳定性较差。

The Qinghai-Tibet Plateau (QTP) is heavily affected by climate change and has been undergoing serious permafrost degradation due to global warming. Synthetic aperture radar interferometry (InSAR) has been a significant tool for mapping surface features or measuring physical parameters, such as soil moisture, active layer thickness, that can be used for permafrost modelling. This study analyzed variations of coherence in the QTP area for the first time with high-resolution SAR images acquired from June 2014 to August 2016. The coherence variation of typical ground targets was obtained and analyzed. Because of the effects of active-layer (AL) freezing and thawing, coherence maps generated in the Beiluhe permafrost area exhibits seasonal variation. Furthermore, a temporal decorrelation model determined by a linear temporal-decorrelation component plus a seasonal periodic-decorrelation component and a constant component have been proposed. Most of the typical ground targets fit this temporal model. The results clearly indicate that railways and highways can hold high coherence properties over the long term in X-band images. By contrast, mountain slopes and barren areas cannot hold high coherence after one cycle of freezing and thawing. The possible factors (vegetation, soil moisture, soil freezing and thawing, and human activity) affecting InSAR coherence are discussed. This study shows that high-resolution time series of TerraSAR-X coherence can be useful for understanding QTP environments and for other applications.

青藏铁路多年冻土区域路基稳定性关系到青藏铁路能否长期安全运营,因此对铁路沿线冻土区进行形变监测有着非常重要的意义。近年来,雷达差分干涉测量(D-InSAR)技术已发展成为监测地表形变的一项重要技术手段。本文利用此技术结合重复轨道ENVISAT ASAR雷达影像数据,获取青藏铁路羊八井-当雄区冻土形变结果,所得形变结果与冻土冻胀融沉的物理变化规律非常符合,说明采用D-InSAR技术提取铁路沿线冻土区域大范围地表形变信息的效果良好。

由季节性的冻胀和融沉导致的地表变形是在多年冻土区域进行工程施工的最主要危害,青藏铁路建设和维护中的一个主要问题就是如何监测冻土的形变.利用北麓河地区的ASAR数据,联系冻土的相关变化规律,对于冻土区域的相干特性进行了分析.通过对不同自然地物的相干性进行对比分析,发现冻土区域地物的相干性不仅与地物特性相关,同时也与冻土的冻结和融化密切相关.不同时间段干涉对的相干性的差别反映了冻土在不同季节的变化规律.青藏铁路和公路在不同空间基线和时间基线上的相干性表现,为该区域的稳定散射体的选择提供了一种可能,对于进行北麓河区域的冻土形变的时间序列分析具有重要的指导意义.