差分干涉SAR冻土形变检测方法研究

季节性冻融导致的地表形变是冻土地区工程建设的主要病害,冻土的冻胀和融沉是影响青藏公路以及目前建设的青藏铁路路基稳定的重要因素.近年来,差分干涉测量技术已成为地表形变测量和监测的重要工具.基于重复轨道的ERS 1/2雷达图像,研究了利用干涉SAR技术探测冻土形变的方法,经过对引入DEM差分干涉SAR技术的处理和分析,得到研究区冻土形变结果.通过与实测数据比较,表明重轨差分干涉测量可以精确地探测冻土表面形变,可用于青藏铁路冻土形变监测.

Detecting the Displacement Field of Thaw Settlement by Means of SAR Interferometry

In the Tibetan Plateau there are 1 272 709 km² and 1 146 399 km² of permafrost and seasonal frozen ground, respectively. The Qinghai-Tibet Railway began to construct in 2002. Permafrost is a disadvantage for engineering construction. There are about 550 km of the railway passing through permafrost regions, including continuous permafrost and some island permafrost. The maximum depth of the active layer at the test site reaches approximately 0.4～1.5 m, the extensive regions of frozen ground hold large amount of moisture in wintertime. The seasonally thawing layer is sensitive to temperature change. It is clear that thawing and temperature rising has a great influence on railway stability. The surface displacement due to seasonally frost heaving and thaw settlement is the main trouble for engineering construction in permafrost regions. One of the maintasks in the operation of the Qinghai-Tibet Highway or the Qinghai-Tibet Railway is to monitor the displacement field of permafrost. The interferometric SAR technique has demonstrated its capability to measure ground deformation in wide range of application. For some applications, especially those involving engineering projects, quantitative application of the InSAR results is required. The seasonal transition of the land surface between frozen and non-frozen conditions affects a number of ecological and hydrological processes. At the same time, the freeze/thaw transition will cause a deformation of ground surface, which is the main factor that should be considered in engineering construction in permafrost regions. In this study, three topics are of special interest. 1) A method developed to map the displacement field by means of InSAR measure with the high accurate DEM; 2) Validation and analysis of the results; and 3) Future work for improving the accuracy of deformation mapping by means of SAR interferometry. Four scenes of SAR SLC images, including Tandem data, are used to produce multiple imterferograms, and 1:100 000 DEM is used to reduce the terrain effect. Using repeated pass differential SAR interferometry, the displacement field is mapped with 0～2.02 cm vertical settlement. The settlement values are validated and compared quantitatively base on precise and accurate geodetic data derived from field measurement, and the environmental characteristics of displacement field are analyzed. The presented results demonstrate that the interferometrical SAR are fairly good for permafrost deformation monitoring, and there is a great potential of SAR data for monitoring the displacement of permafrost caused by frost heaving and thaw settlement for the management of the Qinghai-Tibet Railway. It is believed that short baseline SAR pairs, accurate Delft orbit calculation, further atmosphere correction, and long-time serial SAR data on the study area would help to improve the accuracy significantly.