Abstract
Digital height models (DHM) are a basic requirement for several applications. The generation of DHM is time consuming and expensive, but some nearly worldwide covering height models are available free of charge or commercially and the number and quality are growing. For practical use it is important to have some information about the quality, the accuracy, accuracy characteristics, areas with problems, height definition as digital surface model with the height of the visible surface or as digital terrain model with heights of the bare ground, resolution (point spacing and correlation of neighboured height values), homogeneity and availability. Also morphologic details are important, depending upon the point spacing and relative height accuracy. An overview about the freely available and commercially nearly worldwide covering height models with a satisfying point spacing and accuracy is given. Changes in this area are fast, so only the current status can be described. A really worldwide covering DHM came with the commercial WorldDEM, based on TanDEM-X interferometric synthetic aperture radar (InSAR) from which now also a reduced, free version with 3 arcsec point spacing is available as TDM90. In addition to the highest accuracy in this field with 10 m point spacing, WorldDEM has also very good morphologic details with the exception of city areas. Quality files belonging to WorldDEM include information about areas with problems. Some height models have been analysed by comparison with satisfying reference height models. The characteristics are described as well as the problems of accuracy specifications with different accuracy figures and dependency upon terrain inclination and other parameters, to allow a selection corresponding to the individual requirements. This also includes horizontal shifts or even rotations and higher degree systematic differences between the reference and the analysed DHM.