ScanSAR-to-stripmap interferometric observations of Hawaii

InSAR images of geophysical events such as pre-eruptive volcano deformation or interseismic strain accumulation are often limited by phase distortions from the superimposed atmospheric signature. Additionally, the approximate monthly repeat cycle of many radar satellites cannot accurately capture rapidly time-varying processes. The ScanSAR mode of the Envisat ASAR instrument permits more frequent revisits of a given area, potentially overcoming both of these limitations. In particular, stripmap-to-ScanSAR images provide a denser time series of interferograms than is possible with conventional stripmap-to-stripmap InSAR.; In this work we develop a method to generate efficiently, scanSAR-to-stripmap interferograms. We present a time series of Envisat data acquired over Hawaii in which ScanSAR mode data are combined with Envisat conventional stripmap mode data to form a series of interferograms at a denser temporal spacing than is possible with normal InSAR.; The burst nature of ScanSAR data and the differences in the pulse repetition frequency between the two modes requires a new processing method to form the interferograms. We use traditional matched filtering for the range compression. For the azimuth processing, we compute the stripmap mode data on the ScanSAR sampling grid using a variation, consisting of different reference functions to readjust the azimuth pulse spacing, of Lanari's modified SPECAN algorithm, itself an adaptation of the chirp z-transform. Additionally, we present a method for the co-registration of stripmap data to ScanSAR data. For the fine co-registration we use the linear relation between the phase ramp present across a burst in misregistered stripmap-to-ScanSAR interferograms and the misregistration amount.; The resulting interferograms faithfully reflect the phase of conventional interferograms, but exhibit fewer looks and coarser resolution than those produced by fully stripmap 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.