Measuring ground subsidence in shanghai using permanent scatterer insar technique

The city of Shanghai has been experiencing subsidence since 1921 mainly due to intensive withdrawal of water from underground [1][2], and to some extent due to rapid infrastructural developments taking place in the city (e.g., concentration of skyscrapers in Xuhui District and the Lujiazui Financial Zone of the Pudong District) [3]. Subsidence phenomenon in Shanghai has been previously measured or monitored using the surveyor's method of precise leveling, and more recently the global positioning system (GPS). Although these methods provide precise measurements they are labour and time intensive, costly and are restricted to specific points in the terrain. Inteferometric synthetic aperture radar (InSAR) has demonstrated the capability of mapping extensive areas, on pixel-by-pixel basis, and in a more convenient manner than the aforementioned geodetic methods. In this paper, the strength of using the permanent scatterer (PS) InSAR technique, an advanced form of the conventional differential InSAR technique, is used for measuring ground subsidence in Shanghai. Nineteen (19) ERS-1 and ERS-2 SAR single look complex (SLC) scenes acquired over Shanghai during the period 6 June 1992-20 November 2001 were used for the study. The images have a maximum relative temporal baseline of 3454 days (approximately 9.5 years) and a minimum relative temporal baseline of 1 day. Over 21000 PS were extracted, and preliminary result is in sympathy with some reported studies, as well as the reported annual average subsidence rates based on precise leveling and global positioning systems (GPS) surveys over well established benchmarks in the city.