Land subsidence

Space-borne synthetic aperture radar interferometry (InSAR) is a powerful new geodetic technique providing accurate measurements (cm level) of surface changes over wide areas (typically 100x100 km2). For more than a decade, the method has been widely used to monitor earthquake-induced and volcanic-induced deformation in tectonically active areas. In recent years, InSAR has also been used for mapping and monitoring land-surface in various environments, due to withdrawal of ground water or other fluids (oil, natural gas), soil consolidation, and sediment compaction in flood plains. Land subsidence occurring in urban areas can be monitored by highly accurate Permanent Scatterers InSAR (PSInSAR) technique, which deals better with atmospheric noise and calculates the displacement time series of selected reliable scatteres. We used both standard InSAR and PSInSAR analyses to study land subsidence in New Orleans (Figure 1), the Venice Lagoon, the Dead Sea and the city of Mokpo (South Korea). Our studies show significant subsidence patterns in all locations with variable rate reaching as high as 30 mm/yr.

Figure 1.  Velocity map for permanent scatterers in New Orleans and vicinity.  Values are range change in the direction of radar illumination.  Negative values indicate motion away from the satellite, consistent with subsidence.  Int. Airpt. is location of International Airport, MRGO is Mississippi River-Gulf Outlet Canal. Inset (location marked by white rectangle) shows close up of PS velocity map for parts of eastern St Bernard's parish and western part of Lake Borgne. Note high rates of surface motion (~subsidence) on levee bounding MRGO Canal. Large sections of the MRGO levee were breached during and shortly after Hurricane Katrina in August 29, 2005.

More details at Bear et al (2002) and Dixon et al. (2006)