Investigation of Elevation Bias of the Srtm C- and X-band Digital Elevation Models

The paper presents results of a comparative study of the vegetation-caused elevation bias of the space shuttle topographic mission data product, both Cand X-band (SRTM.C/X). The SRTM.C/X bands data were compared against a high-resolution digital terrain model. Pixel-based differences in SRTM.X minus SRTM.C were correlated with land cover (‘agriculture’, ‘house’, ‘tree’, ‘water’). Findings of the investigations include that the SRTM.X does not represent a canopy top of vegetation and that the X-band penetrates deeper vegetation cover than the C-band. As a test site, an area of about 159 km on the Gold Coast, Queensland, Australia, was selected. The area of interest is about 57% covered by vegetation varying from grassland and shrubs to forest. The study method allowed the development of a statistical model relating the elevation bias to the percentage of the vegetation cover of a given land parcel. This model, once verified on varieties of vegetation types, could be utilised to estimate and eliminate the elevation bias from the InSAR elevation model. This model could also be utilised for estimating biomass quantities and their variations. It is hoped that the results will also stimulate investigations towards developing a multi-frequency InSAR system for collecting both terrain elevation data and attributes of biomass.