CHARACTERISTICS AND ACCURACY OF LARGE AREA COVERING HEIGHT MODELS
Large area covering height models are dominantly based on optical and synthetic aperture radar (SAR) space imagery. The vertical accuracy of individual object points determined by automatic matching of optical imagery is in the range of 1.0 ground sampling distance (GSD), but this is not identical to the accuracy of the height model. With the exception of long wavelength SAR data, the Pand L-band, all height models are originally digital surface models (DSM) and not the most often requested digital terrain models (DTM) with the height of the bare ground which have to be generated by filtering. In addition height models are influenced by interpolation, reducing the geometric quality. Large area covering height models are analyzed for their accuracy and characteristics, including the effect of details influenced by the method of determination. The absolute accuracy in addition is affected by the quality of geo-reference, which partly is based on the direct sensor orientation, partly based on ground control points (GCP) or indirectly on other existing height models. The most important influence for the resolution of a height model is the point spacing of the DHM, but details also can be lost by not proper data handling. All height models have lower accuracy in steep terrain, the matching of optical images is influenced by the object contrast, while SAR is affected by layover. By this reason gaps in the height models often are filled with other data causing more heterogeneous character.