Subway Subsidence Monitoring and Analysis in Beijing through Envisat-Asar and Terrasar-X DATA

Abstract:

Subway plays a significant role in public transport in Beijing, China. The safe operation of such underground rail transports are serious threatened by ground subsidence that mainly caused by groundwater over-exploitation. It is necessary to carry out a continuous observation and analysis of the surface deformation along the newly built rails.

The paper mainly studied four subways which were built in different periods(see attachment). Envisat-ASAR and Terrasar-X images of the study area were selected to measure the ground deformation. Interferometric Point Target Analysis method was gathered to process the SAR data. The method is developed based on the idea of the Permanent Scatterers SAR Interferometry method which can overcome the decorrelation and atmospheric effect to gain more precise estimation of the ground deformation. The master image can be selected according to the perpendicular, Doppler and temporal baselines to minimize the potential decorrelation. After the registration of all slave images to the master image, the PS candidates would be detected on the basis of the scattering properties of the images. A complex operation of the PSs was conducted to obtain the interferometric phase which was composed of terrain phase, atmospheric phase, deformation phase and noise. A model used for the evaluation of the contribution of each component was built by means of the least squares method. The deformation phase would be the remaining of the interferometric phase minus disturbance terms.

Deformation information that came from two different kinds of data was jointly analyzed to reveal the temporal character of the rails before, during and after they were built. The regional LOS(line-of-sight) velocity around a special subway station shows that the rail has suffered from a serious uneven settlement along the rail during the observation period. In addition, time series data revealed the characteristic stages of each PS point. There is a clear accelerating trend of settlement in the construction period of the subway, and the sedimentation velocity would remain very high after a period of the opening of the line. Overall, ground subsidence had a certain delay when compared to the construction and operation of the subway.