Measuring Periodic Ground Motion Using InSAR

While differential interferometry can be used to detect very subtle changes in the ground's surface elevation, as shown in other examples on this site, a new type of analysis that exploits a time series of coherent SAR acquisitions of a given site is being developed at Neva Ridge.

By analyzing the time history of ground motion, one can detect more subtle signals than is possible through the analysis of two coherent images alone. Subsidence "trends" can be extracted from noisy data. There are many examples in the literature of extracting millimeter per year subsidence rates using 10's of observations over time.

In the example presented here, we extend this concept to the detection of periodic ground motion. The seasonal ground motion observed here is most likely due to the aquifer expansion and compression cycle corresponding to seasonal water demand and natural recharge. Twenty ERS acquisitions over an area in Southern California were analyzed for evidence of ground motion that showed a statistically signficant 12-month periodicity. Analysis was carried out on a pixel-by-pixel basis and resulted in the discovery of several localized regions which showed such motion (image to left). The amplitude of this yearly oscillation ranges from 2 millimeters to over 2 centimeters. Neva Ridge is continuing development of this technology, and its application to geophysics, hydrologic science and other areas.

For more information, contact David Cohen