Surface Deformation Monitoring in Permafrost Regions of Tibetan Plateau Based on Alos Palsar Data

The permafrost region of Qinghai-Tibet Plateau is widely distributed with the freeze/thaw processes that cause surface structural damage. The differential interferometry synthetic aperture radar (DInSAR) can detect large scale surface deformation with high precision, thus can be used to monitor the freeze/thaw processes of frozen soil area. In this paper, the surface deformation pattern of Qinghai-Tibet railway was analyzed by using the PALSAR 1.0 raw data of the ALOS satellite (L band) and 90m resolution SRTM DEM data, with the help of two-pass DInSAR method in GAMMA software, and the differential interferograms and deformation maps were obtained accordingly. Besides, the influence of temperature, topography and other factors on deformation of frozen soil were also studied. The following conclusions were obtained: there is a negative correlation between deformation and temperature, and there is a delay between the deformation change and that of temperature; deformation and elevation are positively correlated; the permafrost deformation is also affected by solar radiation that could form variable amplitude variation * Corresponding author: Gang Qiao 1. INTROUCTION The permafrost region of the Qinghai-Tibet Plateau is the highest and largest permafrost area in the middle and low latitudes of the world, and its distribution is shown in Figure 1. Permafrost is below 0°C and contains ice in rocks and soil. Permafrost is very sensitive to the temperature of the soil medium, rich in underground ice (Zhou and Guo, 1982). The annual variation process of permafrost activity layer can be divided into four stages: summer melting process, autumn freezing process, winter cooling process and spring warming process (Li and Cheng, 1996). Therefore, the surface of permafrost shows seasonal frost heave and melting phenomenon, frost heave and melting alternately will lead to the destruction of geological environment, causing collapse, landslides and debris flow and other geological disasters. Known as the "Heaven Road", the Qinghai-Tibet Railway is the longest line of plateau permafrost railway with highest elevation in the world. In order to ensure the normal operation of the Qinghai-Tibet Railway, the Qinghai-Tibet Plateau permafrost deformation monitoring work is particularly important. Figure 1 .Distribution pattern of permafrost in the QinghaiTibet Plateau (after Li and Cheng, 1996) The traditional method for deformation monitoring of permafrost in plateau region is carried out by embedding settler or long-term GPS survey and leveling. Although it can obtain high-precision data, only a few limited sites can be observed due to the limited conditions, and regional deformation could hardly be collected unless a lot of labor force were consumed. Interferometry Synthetic Aperture Radar (InSAR) is a new technique for space-to-earth observation. It has the advantages of all-weather, wide monitoring range, high sensitivity, strong temporal continuity and high spatial resolution. It can make up for the shortcomings of the traditional measurement methods in the frozen area for surface monitoring. InSAR obtains information that reflects ground undulation and surface deformation by interfering SAR images covering different phases of the same region. Qin and Perissin(2015) proposed Permanent Scatterer InSAR (PSInSAR) technology to monitor the surface deformation of the urban area of the Hong Kong Special Administrative Region by using TerraSAR-X and TanDEM-X data and obtained high-precision monitoring results. Simon (2017) used InSAR technology to perform a wide range of deformation monitoring in the permafrost region of the Qinghai-Tibet Plateau.The Differential Interferometry Synthetic Aperture Radar (DInSAR) technique based on InSAR is to remove the terrain phase in the interference phase by performing differential interference processing on the interference image of different phases covering the same region, to obtain phase change information. Wang and Li (1999) used DInSAR technology to monitor deformation of permafrost in northern Canada, which was the first application of DInSAR technology in permafrost monitoring. Xia ,et al.(2002) used the method of combining artificial angle reflector with DInSAR The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLII-2/W7, 2017 ISPRS Geospatial Week 2017, 18–22 September 2017, Wuhan, China This contribution has been peer-reviewed. https://doi.org/10.5194/isprs-archives-XLII-2-W7-1509-2017 | © Authors 2017. CC BY 4.0 License. 1509 technique to monitor the vertical deformation, and got the result of millimeter precision. Berardino, et al.(2002) proposed small Baseline Subset InSAR (SBAS InSAR) technology, using a SAR image with a smaller time and spatial baseline threshold, and improved the accuracy by the least squares method. Jia (2016) used the Small Baseline Subset InSAR (SBAS InSAR) to monitor the permafrost in the Qinghai-Tibet Plateau, and obtained the rate of permafrost change in the study area from 2007 to 2009. 2. STUDY REGION AND DATA