Topographic Phase Recovery from
Stacked ERS Interferometry and a Low Resolution Digital Elevation Model
David
T. Sandwell and Lydie Sichoix
Institute of Geophysics and Planetary Physics,
Scripps Institution of Oceanography, La Jolla, CA
Submitted to Journal of Geophysical Research, March 1, 2000
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Abstract
A hybrid approach to topographic recovery from ERS interferometry
is developed and assessed. Atmospheric/ionospheric artifacts, imprecise
orbital information, and layover are key issues in recovering topography
and surface deformation from repeat-pass interferometry. In a previous
paper, we developed a phase gradient approach to stacking interferograms
to reduce these errors and also to reduce the short-wavelength phase noise
[Sandwell and Price, 1998 and Appendix]. Here the method is extended to
use a low-resolution digital elevation model (DEM) to constrain long wavelength
phase errors and an iteration scheme to minimize errors in the computation
of phase gradient. We demonstrate the topographic phase recovery on 16-m
postings using 25 ERS SAR images from an area of Southern California containing
2700 m of relief; this will be compared with the topography measured by
the Shuttle Radar Topography Mission. Based on a comparison with 81 GPS
monuments, the ERS-derived topography has a typical absolute accuracy of
better than 10 m except in areas of layover. The resulting topographic
phase enables accurate two-pass, real-time, interferometry even in mountainous
areas where traditional phase unwrapping schemes fail. As an example, we
form a topography-free (127-m perpendicular baseline) interferogram spanning
7.5 years; fringes from two major earthquakes and aseismic slip on the
San Andreas Fault are clearly isolated.
