Monitoring the land subsidence with persistent scatterer interferometry in Nansha District, Guangdong, China

Nansha District in Guangzhou, south China, as a well-known rapid urbanization area, is characterized by the widely distributed soft soil prone to land subsidence. Accurate monitoring of surface deformation plays a significant role for the hazard prevention and mitigation. In this study, 21 high-resolution TerraSAR-X satellite images acquired from February 2012 to August 2013 are processed with the persistent scatterer interferometry (PSI) technology to detect and reveal the land subsiding characteristics of Nansha District. Based on the comparisons among the PSI, the GPS measurements, and the civil construction process, the land subsiding characteristics are discussed. The difference between PSI and GPS velocity rates on the line of sight direction is less than 3.61 mm/year, showing fairly consistent agreement. Meanwhile, the PSI results show that the Nansha Automobile Industrial Area, Tongxin Industrial Area, Xinan Industrial Area, Nanheng, and Dugang of Sanjiao town in Zhongshan City were stable, where the subsidence velocities were less than -5 mm/year. The moderate subsidence, whose velocities ranged from -20 to -5 mm/year, mainly occured in the Dayuancun village and Gaoping village of Sanjiao town in Zhongshan City. The severely subsiding areas, where the velocities are more than -20 mm/year, were detected in Nansha Export Processing Zone and Minzhong town in Zhongshan City. For the primary roads and bridges, the newly built bridges, such as Hengli Flyover and southern side of Fuzhou Bridges, were suffering a subsidence velocity from -10 to -15 mm/year. On the contrary, the old roads and bridges turned out to be stable, for instance, the Nanshagang Expressway, Hongqili and Lixinsha Bridges. The civil engineering documents and other related materials show that most of the subsidence took place within the rational post-construction period. However, the subsidence in and around self-constructed substandard houses in the countryside are rather severe due to the lack of sufficient soft soil foundation treatment.