| Abstract | Most geoscientific applications using georeferenced cartographic data need a good knowledge and visualization of the topography of the Earths surface: three-dimensional (3D) information, such as digital
elevation models (DEM), has to be generated or is to be added for a better interpretation of the two-dimensional (2D) data. Since the early emergence of earth observation satellites, researchers have investigated different methods of extracting 3D
information using satellite data. Apart from a few early stereo-images acquired with handheld cameras during the Gemini and Apollo missions, the first experiments to extract 3D data using stereo viewing from space began with the Earth Terrain Camera
(ETC) flown onboard SkyLab in 19731974. Since these early experiments, various analog or digital sensors in the visible or in the microwave spectrum have been flown to provide researchers and geoscientists with spatial data for extracting and
interpreting 3D information of the earths surface. Although the shape-from-shading technique can be applied to optical sensor images in ice sheets and caps with low slopes, stereo-viewing using airborne cameras or digital scanner images was, and
still is the most common method used by the mapping, photogrammetry, and remote sensing communities. However, airborne and spaceborne altimeters, such as lidar become more and more popular. On the part of the spectrum, radar data gives also the
opportunity to extract 3D information using image-processing techniques appropriate to the nature of the data. With SAR data, three main methods have been developed: radargrammetry, interferometry, and altimetry. Radargrammetry is roughly similar to
photogrammetry with stereo images acquisition from different viewpoints. Interferometry uses mainly the SAR signal data instead of the image, and altimetry becomes important sources of data in the 1990s with the scanning radar altimeter to generate
small-scale DEMs. The chapter reviews the different methods and sensors used to extract absolute or relative elevation and assess their performance applied to glaciated regions using the results from various research and university organizations. It
also discusses the respective advantages, difficulties, and constraints of the sensors, the methods, and the technologies to take into account the strength of each when integrating them (input, algorithms, and outputs). |