Measurements and predictions of ground subsidence due to soil consolidation using permanent scatterer InSAR

Many urban areas have been subsided due to various causes, including a withdrawal of groundwater, oil and natural gas, underground excavation, mining and tectonic motion. The impacts of land subsidence are most critical in coastal cities, where land elevation is close or below sea level. These cities are highly susceptible to flooding, as shown last year when New Orleans was flooded by Hurricane Katrina. Subsidence caused by aquifer system compaction associated with ground water withdrawal, or organic soil drainage, often shows continuous but waning slow ground movement with time. Due to residual compaction, subsidence continues even after stabilization of ground water level. In reclaimed land, rapid and waning subsidence rates of the surface also results from soil consolidation by the overburden of increased soil loading over the surface during reclamation works. Here we demonstrate interferometric mapping of surface deformation related to soil consolidation. Twenty three JERS-1 SAR images acquired from 1992 to 1998 were used to estimate land subsidence rate in the city of Mokpo, located in the south western coast of Korea. Large regions within Mokpo are subjected to significant subsidence because about 70% of the city area is a reclaimed land from the sea. Two subsidence field maps were retrieved by means of permanent scatterer InSAR (PSInSAR) adopting constant velocity model as well as hyperbolic model to describe the waning ground subsidence. The results indicate continuous subsidence in some areas with different decaying velocity. The subsidence velocity reaches over 6 cm/yr in the fastest sinking area. The validity of subsidence rates estimated was verified by the comparison with ENVISAT SAR measurements acquired during 2004-2005. Hyperbolic model constrained by our JERS PSInSAR results allows us to better fit the observed subsidence derived from ENVISAT data. The result clearly confirms that PSInSAR techniques coupled with hyperbolic model is valuable tool for monitoring long-term land subsidence characterized by time-varying subsidence rate.