ABSTRACT: Topographic recovery from spaceborn radar and laser ranging: ERS, SRTM, and VCL
Sandwell, David T1 and Gidi Baer2
(1) Scripps Inst. of Oceanography, La Jolla, CA
(2) Geological Survey of Israel, Jerusalem, Israel
The global topography of the Earth will soon be available at a 30-m resolution from three active remote sensing satellites. ERS-1/2 (1992-present) provides high-resolution topography in arid regions where many repeat scenes are available for stacking. The Shuttle Radar Topography Mission (SRTM early 2000) will provide global topography at 30-m resolution. The Vegetation Canopy Lidar (VCL, mid 2000) will provide profiles with 25-m along-track resolution and 1-m vertical accuracy (essp.gsfc.nasa.gov/vcl.html).
Since the ERS satellites were not designed for topographic mapping or interferometric SAR (InSAR), we have developed a recipe for maintaining high accuracy even in mountainous areas. A low resolution DEM provides the long-wavelength accuracy while a stack of more than 16 ERS interferograms provides short-wavelength resolution. The method is applied to the Salton Sea area of Southern California as well as the Dead Sea Rift Zone of Israel and Jordan.
The low-resolution DEM is referenced to WGS84 using the EGM96 geoid. It is converted to topographic phase and then removed from each interferogram. Residual phase gradients are computed, stacked, and unwrapped using an iterative fourier transform method. This residual phase is added back to the crude topographic phase to serve as the reference phase for the next iteration. A comparison with 81 GPS monuments in the Salton Sea area shows vertical accuracy of 10 m at 20 m horizontal postings. Similar accuracy can be achieved in any arid area where more than about 25 ERS repeat scenes are available.
AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia