HR: 11:35h
AN: G42A-05    [Abstracts]
TI: A New Method for Measuring Volcanic Deformation Using InSAR Persistent Scatterers
AU: * Hooper, A
EM: ahooper@stanford.edu
AF: Stanford University Department of Geophysics, Mitchell Building, Stanford, CA 94305 United States
AU: Segall, P
EM: segall@stanford.edu
AF: Stanford University Department of Geophysics, Mitchell Building, Stanford, CA 94305 United States
AU: Zebker, H
EM: zebker@stanford.edu
AF: Stanford University Department of Geophysics, Mitchell Building, Stanford, CA 94305 United States
AB: Persistent scatterer (PS) analysis of InSAR data has proven to be a very sensitive technique for measuring steady deformation in urban areas. Standard methods can also treat non-steady deformation if displacements follow a simple parametric function of time. Applying these methods to estimate deformation on volcanoes is, however, more challenging because a) the majority of volcanoes are not urbanized and therefore lack the man-made structures that are recognized by the PS algorithm, and b) deformation tends to proceed at an irregular rate. We present a new method for identifying PS pixels in a series of interferograms, based on a combination of their amplitude and phase characteristics, that is applicable to the study of natural targets. The phase-based method avoids one major problem with the existing algorithm: low amplitude pixels with actual phase stability are not identified. Our method also uses the spatial correlation of the phases rather than a specified phase history so that we can observe temporally-variable processes. The algorithm involves removing a residual topographic component of the phase for each PS, assumed proportional to the interferometric baseline, and then unwrapping the phase of the PS interferogram stack both temporally and spatially. Our technique finds scatterers with stable phase characteristics, even for pixels that do not contain man-made structures. It is applicable to areas where conventional InSAR fails due to complete decorrelation of the majority of scatterers, yet a few stable scatterers may be distributed amongst them. We created and analyzed a stack of 21 interferograms for Long Valley Caldera in California, and identified 23,000 PS pixels in the study region, as opposed to 300 found with Ferretti's (2001) algorithm. The resulting unwrapped phases, when transformed into estimates of line-of-sight displacements, agree with GPS, leveling and EDM measurements made over similar time intervals, validating the technique. Furthermore, the dense spatial coverage of the PS allows us to refine models of the sources of deformation within the caldera.
DE: 8494 Instruments and techniques
DE: 6924 Interferometry
DE: 1243 Space geodetic surveys
DE: 1294 Instruments and techniques
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting