Groundwater monitoring with InSAR

Farr, Thomas G.
Jet Propulsion Laboratory, Pasadena, CA, tom.farr@jpl.nasa.gov

Groundwater is a significant source of fresh water in arid and semi-arid regions, but one that is difficult to monitor. In developed areas, wells can be drilled which are used both for extraction and for monitoring groundwater levels. However, the expansion and contraction of aquifers due to recharge and withdrawal of water can cause deformation of the Earth's surface which can be observed and measured by InSAR. Repeat-pass InSAR has been shown to be highly sensitive to surface deformation related to earthquakes, volcanoes, and fluid movements including oil and water. In particular, several studies have shown inflation and deflation directly correlated to recharge and withdrawal of water in Las Vegas, Phoenix, and Los Angeles. Time series of these data show a clear seasonal signal which correlates with groundwater levels in wells. Initial results from a study of California's Central Valley show that with C-band systems such as Envisat, decorrelation due to crops and plowing may be a major problem, but that there are enough towns and other areas that remain correlated so that the concept is still feasible. An important requirement is for continuing monitoring for at least a decade. A proof of concept study is now under way for a large part of the Central Valley.