Comparison of DEMs Derived from InSAR and IRS-1C Optical Stereo Techniques
S. Yalamanchili Rao(1) and S. Kota Rao(1)
Indian Institute of Technology,
ERS-1 & 2 Interferometric SAR (InSAR) and optical stereo techniques were used to generate digital elevation models (DEMs) for two test sites, each covering 25 km x 25 km area. The ERS-1/2 tandem data acquired during April, 1996 and optical stereo data of IRS-1C PAN acquired in Feb. 2002 were processed using Gamma and PCI Geomatica OrthoEngine software respectively. Heights from topomaps and GPS measurements were used as ground control points in the process of DEM generation.
A comparison is made between the DEMs derived from InSAR and optical stereo techniques. It is found that the SAR DEM is better than that of DEM derived from IRS-1C PAN in terms of elevation contour. The contours from InSAR DEM are very fine as compared to that of optical stereo. The number of regions where DEM is not possible to obtain (i.e. holes) are also more in the optical DEM. However, RMS deviation (30 m) is more for InSAR DEM than that of optical DEM (16 m). It may be due to the difficulty of identifying the corresponding points in both the images with respect to topomaps as the SAR intensity data is prone to speckle noise. When we compared the DEMs with GPS values for another site, we observed the RMS deviation for both DEMs is about 15 meters. Optical stereo failed to produce DEM at some locations where the steep slopes face away from the sensor, whereas SAR gave good DEM over the same area. However, optical stereo gave better results for slopes facing towards the sensor, while SAR suffers from layover and foreshortening effects at those places. In view of the complimentary characteristics of the two techniques, an attempt is made to merge the DEMs to get a better DEM.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,