Influence of satellite imaging geometry on ASTER and SRTM global digital elevation models

Περίληψη

In this paper we assess the accuracy of ASTER and SRTM height estimates, investigating the spatial distribution of their deviations from a reference height dataset derived from topographic maps. The analysis is performed over the hydrological basin of the Xerias River located at the northeastern part of Peloponnesus. The selected area exhibits complex terrain allowing for the detailed evaluation of the influence of local topography on the satellite height estimates. The aim was to identify regions where deviations exist, recognize potential spatial patterns and verify whether they are controlled or not by specific morphological parameters. The investigation included geostatistical analysis of height differences with respect to parameters such as elevation, slope gradient, slope aspect and morphological units. Regression analysis results showed both systematic and non-systematic trends. For ASTER the deviations are limited to a global shift, while of importance is the positive correlation between the spatial distributions of deviations and aspect for the SRTM model. Further analysis included simulation of the SRTM imaging geometry to support understanding of the observed height deviation. It was verified that the sign and magnitude as well as the location of the deviations are related to the methods of height extraction from space-borne systems, being more pronounce in the SRTM model as a result of the side looking configuration of SAR sensors. These findings underline that the source of deviations in satellite derived height models should not be fully attributed to local morphological characteristics, since space-borne imaging is contributing significantly, paving the way for a more adequate utilization of these global elevation models.