| Abstract: |
In a current California Energy Commission (CEC) project, satellite radar interferometry (InSAR) is applied to detect surface deformation in several areas of the Imperial Valley in southern California. These areas include established, new and possible future geothermal fields, as well as nearby fault zones. The InSAR technique used, SqueeSARTM, is the latest innovation in the field of radar interferometry. It makes it possible to obtain deformation time series at locations of permanent and distributed scatterers (PS and DS), playing the role of numerous benchmarks. The deformation time series are then used to estimate annual deformation rates. The PS represent points aligned along roads and canals, buildings, wellheads, etc., which remain coherent from one satellite image to another. The DS cover several pixels in the satellite scenes and emit weaker signals than the PS, but still above the backscatter noise. The SqueeSARTM technique works well for vegetated and rural areas and thus provides unique results from the agricultural lands of Imperial Valley. The radar scenes used for the analysis are from the Envisat satellite, over the period 2003-2010. Two data sets were used, consisting of 45 descending and 33 ascending images, for which the satellite moved from north to south and south to north, respectively. In this paper the focus is on three geothermal fields – Salton Sea (SSGF), Heber (HGF), and East Mesa (EMGF). Preliminary results show that distinct areas of subsidence are seen in all of these fields. Earlier results from a two-year study using data from another satellite for the SSGF, are confirmed in the present work. At the HGF, there is also evidence of uplift. Radar interferometry provides unprecedented information on surface deformation, with great spatial and temporal detail, which cannot be achieved by any ground-based means. In this capacity, it has applications for pre-production reservoir assessment, ongoing exploration, and mitigation of any environmental impact that might occur. |