Evaluation of the elevation model influence on the orthorectification of Sentinel-2 satellite images over Austria

Abstract

The European Space Agency (ESA) is using PlanetDEM for the generation of their Sentinel-2 Level-1C orthophotos. There are concerns that this DEM is not accurate enough for this purpose, especially over mountainous regions like in Austria. In this study, we investigate the height accuracy of PlanetDEM in Austria by comparing it with a reference DEM that is derived from airborne laser scanning. Afterwards, we predict the errors in the Sentinel orthophotos that are caused by these DEM errors: 99.8% of all pixels have a PlanetDEM-induced displacement between ±10 m (i.e. one Sentinel-2 pixel) for all investigated four satellite tracks over Austria. Still, at a few spots, the location errors can reach 60 m. ESA’s goal is to achieve a multi-temporal geo-registration quality (for Level-1C products) of 3 m (95.5% confidence) once the Global Reference Image is established. If we assume that this error budget consists partly of a georeferencing and partly of a DEM-induced error and both are equal, then the DEM-induced error may only amount to 2 m. In this case, PlanetDEM would not allow for this accuracy in the mountainous regions, because there, according to the predictions of this study, 95.5% of the errors are between ±3.8 m.