Test site 3. Makmal - Satellite based DEM extraction
Digital Elevation Models (DEMs) are required for several tasks like generation of orthoimages, generation of contour lines and for many geographic information system applications, including spatial risk assessment. Different data sources do exist ranging from airborne photogrammetry airborne LIDAR systems to airborne and spaceborne InSAR approaches. DEM based on spaceborne systems are a cost effective alternative in comparison to more expensive airborne surveys.
The accuracy mainly depends on the parameter image resolution, height-to-base-relation and image contrast. As automatic measurements are done by image matching techniques, the first data set created is a Digital Surface Model (DSM), which points are located on the visible surface, including the heights of the different natural or manmade land-use classes. Thus, filtering techniques deleting non-ground pixels and filling the existing gaps by interpolations afterwards have to be applied. This causes a comprehensive quality control before any further application can take place.
DSMs for Sokolov have been generated using CartoSAT stereo images for 2009, 2010 and 2011. For Kazarman (2010) and Witbank (2011) WorldView-II stereo images have been used.
Generating DEMs from stereo data normally requires the use of a geometric model (rigorous physical sensor model) and ground control points (GCPs). The collection of GCPs presents a significant problem in many practical applications, as an existing source of GCPs may not be available. Rational Polynomial satellite sensor models are simpler empirical mathematical models relating image space (line and column position) to latitude, longitude, and surface elevation. This approach is applicable for both sensor systems used. Matching homologous points has been done by using an operational DLR processor based on a semi-global matching (SGM) algorithm. After outlier removal and transformation into the Universal Transverse Mercator (UTM) projection, a DSM with 5-m grid spacing has been generated (Arefi et al. 2011).
Sokolov - Cartosat 2009 DEM (left pair) and 2010 DEM (right pair). Each pair displays with no-correlation holes (left) and the SRTM data filled DEM (right).
Perspective view on the shaded relief calculated from the WV-II DEM for Kazarman