DIGITAL TERRAIN MODEL (DTM) FROM INDIAN REMOTE-SENSING (IRS) SATELLITE DATA FROM THE OVERLAP AREA OF 2 ADJACENT PATHS USING DIGITAL PHOTOGRAMMETRIC TECHNIQUES

Present day needs for medium- and small-scale topographic mapping at r educed cost and time can be met by using stereoscopic digital data acq uired by present and planned satellites. In anticipation of the planne d IRS-1C stereo data, attempts are made to use the overlap area betwee n two adjacent paths of IRS-1A linear imaging self scanning (LISS)-II data as a stereo pair for generating a digital terrain model (DTM) usi ng digital photogrammetric techniques. Software has been developed to recover the epipolar geometry of the stereo pair and to accomplish aut omated digital stereo matching to find the corresponding points in the left and right images by correlation techniques to calculate parallax to the sub-pixel level. The parallax is then used in conjunction with the IRS-1A data acquisition system to compute relative elevations. Th e absolute DTM is generated by referring the relative elevation to a f ew control points with known Z-coordinates. To evaluate the developed methodology and the software, three test sites at different locations in India near Palghat, Pune, and Dehradun were selected. It is observe d that the overlap area between two adjacent paths increases from the equator to the poles whereas the base-to-height ratio (B/H) decreases. A methodology to calculate the percentage of overlap and BIH value at a given latitude is presented. The resultant DTMs for the three test sites were evaluated for error, and it is observed that 90 percent of RMSz errors fall within 33.95 m, 34.45 m, and 38.12 m at Palghat, Pune , and Dehradun, respectively. The DTM and the corresponding IRS-ZA dat a are used to generate 3D perspective images. The software package dev eloped will have potential usage in 3D analysis of IRS-1C stereo data.