HR: 09:30h
AN: G41D-07    [Abstracts]
TI: Analysis of deformation on Hawaii using ScanSAR-strip mode interferometry to achieve a denser time series
AU: * Bertrán Ortiz, A
EM: nuska@stanford.edu
AF: Department of Electrical Engineering, Stanford University, 322 Packard Building 350 Serra Mall, Stanford, CA 94305-9515 United States
AU: Zebker, H
EM: zebker@stanford.edu
AF: Department of Electrical Engineering, Stanford University, 322 Packard Building 350 Serra Mall, Stanford, CA 94305-9515 United States
AB: Subtle crustal deformation phenomena such as interseismic strain accumulation or pre-eruptive deformation of volcanoes can produce such small surface deformation signatures that they are undetected in single radar interferograms. Interfering factors such as temporal decorrelation noise caused by vegetation and phase distortions due to propagation through a spatially variable troposphere can easily obscure useful signals. These phenomena may be minimized by reducing the time between acquisitions and increasing the number of acquisitions. Acquiring deformation at a denser time sampling is also critical in the observation of rapidly time-varying processes. The Envisat satellite permits multiple observations of an area within a single orbit cycle due to its electronic beam steering capability, whereby a region of interest is observed by the sensor on several orbit tracks. This rapid beam switching, or ScanSAR operation, also enables the imaging of wide swaths. For Envisat, each point on the ground can be imaged five times during a cycle. Here we present an analysis of Envisat data acquired over Hawaii in which data acquired roughly weekly in ScanSAR mode are combined with Envisat conventional strip mode data to form interferograms at a much denser temporal spacing than is possible with normal InSAR. Some technical challenges associated with creating a strip mode-ScanSAR interferogram stem from the differences in the data acquisition. While strip mode data are acquired continuously, ScanSar data are composed of a limited burst of pulses for each subswath. The two modes also differ in their azimuth sampling rate. We use traditional matched filtering for the range compression. For the azimuth processing, we compute the strip mode data on the ScanSAR sampling grid. This is done by i) using Lanari's modified SPECAN (Oppenheim's chirp z-transform) algorithm to specify the azimuth spacing, ii) by identifying the correct start pulse in the IM data and iii) by estimating and applying the necessary non-integer gap between bursts. The resulting interferograms faithfully reflect the phase of conventional interferograms, but exhibit fewer looks and coarser resolution than those produced by fully strip mode data. For many problems temporal density of the deformation observations is paramount and the time series analysis and temporal averaging made possible using ScanSAR interferograms far outweighs the loss in looks and resolution.
DE: 1241 Satellite geodesy: technical issues (6994, 7969)
DE: 1294 Instruments and techniques
DE: 6924 Interferometry (1207, 1209, 1242)
DE: 6969 Remote sensing
SC: Geodesy [G]
MN: Fall Meeting 2005