Assessing the accuracy of SRTM altitude data for the hilly area in northeastern Romania

SRTM data is still one of the most used data in geosciences for various purposes: geomorphometric analysis, environmental covariate modelling or geomorphic change detection. Although high resolution national/regional DEMs exist, very often accessing them is expensive, or their coverage is not complete over specific areas (only floodplains or cities are covered). Because of this SRTM still remains the best choice when elevation data is needed for regional/national or global areas. In order to assess the correctness of SRTM data to depict the real shape of Earth surface we used a regional high resolution DEM which cover a part of the hilly area of north-eastern Romanian. Both DEMs were converted to the same horizontal and vertical datum (Stereo 70 Romanian projection and the EGG97 geoid), interpolated to the same grid size and position and compared using raster algebra. The horizontal x and y components and the vertical component errors were assessed. The results show that the errors of the SRTM model are well consistent with its acquisition method (the presence of the trees and the topographic shadow) and does represent reasonably well the Earth’s surface in the study area. Anyhow, the resolution of the Earth features depicted on the SRTM model is limited by the acquisition method and does not incorporate landforms which have a vertical and horizontal wavelength under 100 m.