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Application of SAR – interferometry and global positioning system to digitan elevation model generation and evaluation

N. Phani Kumar1, M. N. Kulkarni1 and K. S. Rao2
1Department of Civil Engineering, IIT, Mumbai – 400 076
2Centre of Studies in Resources Engineering, IIT, Mumbai – 400 076

Digital Elevation Models (DEM’s), which comprise the process of representing the elevation characteristics of the terrain in discreet form in a three-dimensional space or in the form of an equation of a surface, have acquired wide range of applications in many scientific and engineering fields. Some of the important applications are: estimation of Earth-work in cut and fill for roads / canals, selection of sites for dams and tunnels, etc. DEM’s can be generated by using various techniques, ranging from classical terrestrial surveying to modern satellite techniques. Synthetic Aperture Radar (SAR) Interferometry is one of the recent techniques (a spin-off of Microwave Remote Sensing), being used to generate DEM’s.

In SAR-Interferometry two images are acquired from two slightly different positions with both the images covering the same area. SAR images consist of information about back-scattered energy and phase of the signals. In this technique, the two SAR images are registered to the sub-pixel accuracy to generate the interferogram, which consists of the combined phases of the two images. This phase information at each pixel in the interferogram will be in accordance with the topography of the terrain at the respective pixel positions. These phases are then unwrapped to get the heights of the points.

The aim of this study is to generate the Digital Elevation Model (DEM) by using the SAR Interferometric technique and to evaluate it by using the Global Positioning System (GPS). It is planned to generate a DEM of Mumbai test site, using the ERS1/2 tandem data with the help of GAMMA software. To evaluate the SAR DEM, GPS measurements will be taken at some specific points identified on the image. Both SAR DEM and the GPS give the heights above the WGS-84 ellipsoid.