MAPPING SUBSIDENCE WITH SATELLITE RADAR INTERFEROMETRY

This presentation summarizes the use of interferometric synthetic aperture radar (InSAR) for measuring land subsidence. Current space-based SAR systems provide monthly imagery over a given location spanning ~100 km by 100 km at a horizontal ground resolution of tens of meters. Two SAR images over the same location can be combined to form a radar interferogram. The resultant InSAR phase measurement is sensitive to the topographic height of the surface being imaged and any ground motion that occurred between the two radar acquisition dates. Under ideal conditions, InSAR can be used to measure sub-centimeter deformation along the radar line-of-sight. However, changes in the ground surface over time results in image areas that are uncorrelated and no reliable deformation measurement. The variability of the atmosphere over time and space poses additional problems. In the presence of these effects, an interferometry expert can identify centimeter-scale subsidence in a single interferogram. The frequency at which the radar operating can greatly influence the successful measurement of subsidence over time. C-band InSAR yields good subsidence measurements in arid environments such as Phoenix but produces poorer quality subsidence information in vegetated locations such as the Texas Gulf Coast. However, recently-developed InSAR processing strategies as well as lower frequency L-band SAR systems show great promise in mapping coastal subsidence.