A study on the applicability of repeat‐pass SAR interferometry for generating DEMs over several Indian test sites

Abstract

Repeat‐pass synthetic aperture radar interferometry (InSAR) appears to be an excellent tool for generating digital elevation models (DEMs) of high spatial and vertical resolution. However, in recent years, it has been noticed that the atmosphere causes errors in the elevation accuracy. The objective of this paper is to try to identify climatic regions in India where InSAR can be used for generating DEMs. A detailed study was carried out to quantify atmospheric effects on the DEMs derived from repeat‐pass InSAR. Three test sites were selected for the analysis: one over Mumbai, which is a part of the western ghats region with hilly terrain, lakes and forests; another is the Kolar area with gently undulating terrain with agricultural and forested lands; and the last was Bhuj, an arid plains region which is close to the Rajasthan Thar desert, India. Six interferograms of the Bhuj area derived from two tandem pairs were analysed and it was found that there were varying atmospheric effects of the order of 0.2λ to 1λ and at specific locations more than λ. In the case of the Mumbai and Kolar study areas with two interferograms each, the atmospheric effects were almost negligible. In these cases, it is shown that it was also possible to estimate the height of buildings to an accuracy of 1–2 m. Therefore, it is concluded that one should be cautious when using InSAR techniques for generating DEMs of desert/arid regions where the climate may be very dynamic and only small amounts of water vapour can cause strong atmospheric artefacts.

Acknowledgments

The research team is grateful to ISRO‐IIT(B) Space Technology Cell (Mumbai), Department of Science and Technology (DST) (New Delhi) and the Ministry of Human Resources Development (MHRD) (New Delhi) for sponsoring this project; ESA for providing the required datasets free of charge under AO‐04 (Announcement of Opportunity‐04) project; DLR Germany for providing the X‐SRTM DEM of Bhuj; and NASA/JPL/NGA/USGS for providing the C‐SRTM DEMs shown in this study. The authors would like to thank Mr Parag Narvekar, IIT Bombay, for his help at various stages of the work and Cristiano Giovando, UCL, for producing the colourized hill‐shaded SRTM DEM of India.