Synthetic Aperture Radar (SAR) is a side-looking, active (produces its own illumination), radar imaging system that transmits a pulsed microwave signal towards the earth and records both the amplitude and phase of the back-scattered signal that returns to the antenna. Interferometric SAR (InSAR) is a technique that compares the amplitude and phase signals received during one pass of the SAR platform over a specific geographic area with the amplitude and phase signals received during a second pass of the platform over the same area but at a different time. InSAR techniques, using satellite-based SAR platform data, can be used to produce land surface deformation products with cm-scale vertical resolution, 30-m pixel resolution, and covering areas 100 km x 100 km (in standard beam modes).

ADWR has been using InSAR since 2002 to determine the spatial extent, deformation rates, and time-series history of more than sixteen land subsidence features within the Phoenix, Pinal and Tucson Active Management Areas (AMAs), and several groundwater basins outside Active Management Areas in Maricopa, La Paz, and Cochise Counties. With funding from NASA, and technological help from the Microsoft Vexcel Corporation and the Center for Space Research at the University of Texas at Austin, ADWR has developed an application using SAR data and InSAR processing techniques to perform long-term monitoring of land subsidence within Arizona for the purpose of improved water resource management.