Application Of D-InSAR For Land Subsidence Monitoring In Tangshan

Land subsidence is a phenomenon of environmental geology that the land elevation descend slowness caused by many factors, with the development of the city, the damage of the land subsidence became more and more severe. It has a major characteristic of widely distributed, not easy to detect, most cities in the north and many cities and area along the shore in our country suffer from land subsidence, it influences the economical development and harms to people's life. So it has important significance to monitor land subsidence and its development process in time and truly. Interferometric Synthetic Aperture Radar (InSAR) was developed in recently years; it had become one of the most potential techniques because it could sample densely, have higher accuracy than GPS, measure the land subsidence in the short cycle, and not to build received on the ground.Since have mining in Tangshan, it caused large area subsidence in downtown, at the same time, exploitation of underground water also caused land subsidence. By bouncing radar signals off the ground surface from the same point in space but at different times, the radar satellite can measure the change in distance between the satellite and ground (range change) as the land surface uplifts or subsides.This paper showed the principle and method of D-InSAR in land surface monitoring, illuminated the process of D-InSAR with DORIS, and the key arithmetic in DORIS were analyzed, such as coregistration, reference phase subtracting, topography subtracting using DEM, geocoding. The author collected several ERS and ENVISAT images from 1996 to 2006, and the subsidence of different times and annual average subsidence rate in Tangshan was derived from two pass differential interferometry using DORIS. The author also systemically analyzed the error in interferograms. The major work and results are presented below:(1) Compare with conventional survey technique, InSAR technique has remarkable advantage.InSAR technique can watch every time, cover large area, and get image more quickly. It can not also supply image of hardly measure area which most method cannot, but also can put up high quality surface subsidence which can compare with conventional method. It can supply long time span SAR image and it is low cost.(2) D-InSAR especially suit land subsidence in city. Because of low cover of vegetation and few change of land use in city, it's very good to InSAR. Reversely, because of high cover vegetation in area around city is not good to have InSAR.(3) The author summarized a new method to monitoring the land subsidence in mining area, it supplies a effective approach to study land subsidence and the trend of subsidence.(4) The trend of land subsidence in Tangshan is from acute to slowness. Since 1999, it's forbidden to mining in Tangshan downtown, and Tangshan has been in the list of state's subsidence area which should be restored, the condition of subsidence in Tangshan has been controlled effectively.