Deformation monitoring in Shanghai maglev area

As a very fast traffic tool, the stability of the roadbed of Shanghai maglev is very important. However, the geological condition in Shanhai is very poor and the ground subsidence is severe. So, it is necessary to monitor ground subsidence in the area along the maglev precisely. For half a century, precise levelling method has been used to survey the ground subsidence in Shanghai. But the levelling points are so sparse that we can not get the regional ground subsidence information in details. The emergence of differential synthetic aperture radar interferometry (DInSAR) technology make up for this deficiency, which can detect ground subsidence in a wide area. Over the past decade, DInSAR comes into playing a valuable part in monitoring ground subsidence. Especially, small baseline differential SAR(SBAS) technique based on DInSAR technology can get the useful deformation using only a few radar images. In this paper, ENVISAT ASAR data are used to extract ground subsidence information using SBAS method in Shanghai maglev area. The results show that there is no significant ground subsidence on the maglev line. There are a few places with significant local subsidence rates at about -20mm/y near the railway line.