| Abstract: |
Interferometric synthetic aperture radar (InSAR) is applied to data from the TerraSAR-X (TSX) satellite, collected in the period August 2012 ? October 2013 in the area of the Salton Sea geothermal field in southern California, for the purpose of detecting surface deformation. These data are from a new generation of satellites, with much improved spatial resolution and frequency of temporal coverage than earlier satellites like Envisat (2003-2010). The particular technique applied, SqueeSARTM, uses permanent and distributed scatterers, which makes it possible to observe deformation in agricultural areas, where conventional InSAR does not work. Surface deformation is first obtained in the line-of-sight (LOS) to the satellite from two orbital geometries, descending and ascending. The two LOS measurements are then used to calculate horizontal and vertical displacements. The TSX deformation time series and annual rates are compared with those previously derived from Envisat. The periods covered by the two satellites present an unprecedented opportunity to observe ongoing post-production surface deformation at the CalEnergy units of the geothermal field, operated since early 1980?s, and both pre- and post-production deformation at the new Hudson Ranch-1 (HR-1) development of EnergySource, which started in early 2012. Two subsidence bowls at the CalEnergy units have been confirmed by the TSX results, similar to earlier Envisat observations, with annual subsidence rates of up to ?30 mm/year relative to a benchmark on Obsidian Butte (S-1246). However, there is a clear difference between the pre- and post-production periods at the new HR-1 development, with a relative uplift (compared to S-1246) turning into a subsidence of up to ?18 mm/year. Nonetheless, the possibility for anthropogenic origin of the surface deformation at this field is challenged by non-anthropogenic factors associated with the regional and local tectonics, as well as the receding Salton Sea. |