PERMANENT SCATTERER INSAR: A HIGH-RESOLUTION TOOL FOR DETECTING AND ANALYZING AQUIFER-SYSTEM RESPONSE IN HEAVILY PUMPED GROUNDWATER BASINS IN THE ARID WESTERN US

The application of interferometric synthetic aperture radar (InSAR) studies to hydrogeological problems has advanced rapidly during the last decade, and it is now applied routinely to a wide range of groundwater resource issues including aquifer-system response and resource management. Permanent scatterer InSAR (PSInSAR) provides an additional new high-resolution methodology for detecting and precisely measuring long-term and seasonal aquifer-system response to pumping and recharge. In contrast to the conventional InSAR methodology, the permanent scatterer (PS) methodology utilizes coherent radar phase data from thousands of individual radar reflectors on the ground to develop displacement time series and to produce velocity field maps that depict time-dependent aquifer-system response with a high degree of spatial detail.

In this study, we present the first results of a prototype study in Las Vegas Valley, Nevada, that demonstrate how the PS methodology can be utilized in heavily pumped groundwater basins of the arid western US to analyze aquifer-system response to long-term and seasonal pumping. We used 50 ERS-satellite and 19 ENVISAT-satellite acquisitions to develop a series of velocity field maps of the valley for the 1992-1996, 1996-2000, and 2003-2005 time periods. The PS results show that despite rising water levels associated with an artificial recharge program, long-term, residual, inelastic aquifer-system compaction (subsidence) is continuing in several parts of the valley. In other areas, however, long-term subsidence has been arrested and locally reversed. The seasonal, elastic responses to alternating pumping and recharge cycles were segregated from the long-term trends and analyzed for spatial and temporal patterns. The results show oscillations in which the maximum seasonal responses are associated with the late stages of the annual artificial recharge cycles, and that similar seasonal subsidence signals are related to summer pumping cycles. The differentiation of the seasonal response through the use of PS time series data further allows the estimation of elastic and inelastic skeletal storage coefficients, providing a basis for future work that could characterize the storage properties of an aquifer system with a high degree of spatial resolution.