DEFORMATION MAPPING IN CHALLENGING TERRAINS

In this paper we present an overview of potential mapping and monitoring of faults and other deformation related features aided by various remote sensing technologies, concentrating on radar. Radar images have long been used to discern geologic structure in vegetated terrains. Commonly available radar images from short wavelengths such as X-band (3 cm) can show structure in some detail but actually image the top of the vegetation layer, which reflects the underlying features. Longer wavelength imaging radars such as P-band (~70cm) have been demonstrated to penetrate all the way to the ground in rather dense forest. Discrimination of surface materials in such radar images can thus aid in mapping geologic structures. In addition to images, high resolution digital elevation models (DEMs) are extremely useful in mapping surface expression of tectonic features. Thru use of airborne single pass radar interferometry high resolution DEMs covering large areas are possible. P-band derived DEMs will reveal surface topography in vegetated terrain. Structure reflected in subtle topography is thus revealed. Such data have been acquired by the NASA/JPL AIRSAR/TOPSAR (http://airsar.jpl.nasa.gov/ ) instrument and are also becoming commercially available from instruments such as GeoSAR (http://www.earthdata.com/geosar.htm ). Additionally, interferometric synthetic aperture radar (InSAR) enables direct, geographically comprehensive, measurement of active surface deformation due to tectonics, subsidence due to ground water and petroleum withdrawal, or other phenomena. The InSAR technique compares radar observations made over time as surface movement changes the phase of the received signal which is converted into a mm level precision measurement of surface deformation. Unfortunately existing InSAR capable satellites were not designed for this application and use short wavelengths (C-band, 5.8 cm) which not only does not penetrate vegetation, but suffers from decorrelation as scene details change over time. While there are techniques which can overcome some deficiencies, a longer wavelength InSAR specific system as recommended in the Solid Earth Science Working Group report would enable regional tectonic monitoring (SESWG- http://solidearth.jpl.nasa.gov/PAGES/report.html).