Application of persistent scatterer and small-baseline SAR interferometry in monitoring the surface deformation in the Choushui River Alluvial Fan of central Taiwan

Groundwater overexploitation has caused serious land subsidence in the Choushui River Alluvial Fan (CRAF) area of central Taiwan. Traditionally, the extent and magnitude of the surface subsidence was determined by precise-leveling, however, the cost and spatial and temporal density of the traditional survey prevent the understanding of the full extend of the effect. In this study we implement the Persistent Scatterer and Small-baseline SAR Interferometry, which provides much better spatial resolution, to investigate the surface deformation in CRAF where the water withdraw was serious since long time. Twenty-three radar images, acquired by the European radar satellite ENVISAT from June of 2004 to September of 2008, were used to analyze the surface deformation in the study area. From our results, the most serious subsidence areas are in the middle and distal fan of CRAF, the pass way of the Taiwan High Speed Rail, where the maximum deformation rate is nearly 7 cm/yr along the radar Line-Of-Sight direction. Moreover, it also reveals an obvious subsidence zone in the coastal industrial area of Yunlin with different deformation trend from north to south. Finally we compare our results with the precise-leveling data, the continue GPS data and groundwater level data within the region. It illustrates that the surface deformation in CRAF is related to the seasonal fluctuation of groundwater, which are the high deformation rate in dry season and the low deformation rate in wet season.