| Abstract: |
Interferometric synthetic aperture radar (InSAR) is applied to data from the Envisat satellite, collected in the period 2003- 2010, to detect surface deformation at the Heber geothermal field in Imperial Valley of southern California. The particular technique applied, SqueeSARTM developed at TRE, makes use of permanent and distributed scatterers. This makes it possible to observe deformation in agricultural areas, where conventional InSAR does not work, so our results are the first of this kind for Heber. Observations are obtained first in the line-of-sight (LOS) to the satellite from two orbital geometries, descending and ascending, and are subsequently used to calculate horizontal movements in the west-east direction, as well as vertical displacements. Maps of annual deformation rates derived from the satellite data (2003-2010) show two adjacent areas of subsidence and uplift at Heber, confirming observations from annual ground-based leveling surveys. As to the horizontal movements in these areas, they are westward in the uplift area and eastward in the subsidence area. Maximum LOS rates away from the satellite (indicative of subsidence) reach ?46 mm/year, while maximum LOS rates toward the satellite (indicative of uplift) reach +22 mm/year. However, the uplift is only taking place after 2005, prior to which the leveling data show mostly subsidence traced back to the beginning of leveling data availability from 1994. These changing trends of surface deformation in the 2003-1010 uplift area can be readily traced to changes in injection volumes. Examples of rates along profiles and mean deformation time series within small polygons of interest are also shown. The results demonstrate the utility of InSAR for geothermal operations management, planning, and environmental impact mitigation. |