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Validation of Digital Elevation Model derived from Shuttle Radar Topography Mission using GPS field measurements

K. S. Rao


K. S. Rao
E-mail: [email protected]

Santosh Phalke
Centre of Studies in Resources Engineering
Indian Institute of Technology Bombay
Powai Mumbai 400 076, India

Abstract
Shuttle Radar Topography Mission (SRTM) was a cooperative effort by USA, Germany and Italy launched in February 2000. The duration of the mission was 11 days. The objective of this mission is to generate very accurate (about 5-10 meters) elevation with high spatial resolution (25 x 25 meters) Digital Elevation Data (DEM) of the entire land mass between 58 degrees N to 60 degrees S. The DEM will be generated using SAR interferometry technique at two frequencies (X- and L-bands). The merging of Ascending/Descending and different bands lead to precise DEM in WGS84 datum

A national coordinated program was conceived by Department of Science and Technology Govt. of India to conduct a series of experiments synchronous with SRTM Flights by installing corner reflectors (CRs) for the validation of positional and elevation accuracy of the DEM derived by SRTM. The program was Coordianted by Prof.K. S. Rao, CSRE, IIT Bombay in collaboration with several national institutions in the country. About 14 test sites spread all over India were identified for the installation of CRs. The study themes of these test sites are landuse/landcover, land slides, glaciers, earthquake prone areas and forest sites. About 4 CRs were installed in each site synchronous with SRTM passes.

We received the DEM of STRM of Bhuj earthquake area in India which experienced severe earthquake in January 2001. The DEM is 50 x 50 km area around Bhuj. The main objective of processing this DEM is to validate its positional and elevation accuracy. Subsequently the same methodology will be adopted for the other test sites when the DEMs of those sites are made available from DLR Germany.

A series of Field experiments were conducted with D-GPS systems to measure the elevations (in WGS84 datum) of about 30 locations spread all over 50 x 50 km area of DEM. The DEM was processed using ERDAS and ENVI image processing software packages for three dimentional visualization and extraction of the elevations at the locations of D-GPS measurements.

Several graphs were plotted for the analysis of the data. From the graphs and the Tables, it can be seen that the elevation accuracy of the DEM derived from SRTM was with in 5 meters and the location accuracy was with in two to three pixels. The results of the analysis will be discussed in the full paper. The DEM will be used for generating drainage patterns which in-turn will be of use for hydrological and agricultural studies.