Estimation of the real elevation values on flood basins and lowlands based on SRTM and CORINE data
ISBN 978-85-88783-11-9
Authors
1Ungvári, Z.; 2Gede, M.
1DEPT. OF CARTOGRAPHY AND GEOINF., EÖTVÖS LORÁND UNIVERSITY Email: ungvarizs@map.elte.hu
2DEPT. OF CARTOGRAPHY AND GEOINF., EÖTVÖS LORÁND UNIVERSITY Email: saman@map.elte.hu
Abstract
Since the publication of the SRTM digital elevation model (DEM), a lot of maps were made using it to their relief representation. Map makers can easily use it as a hypsometric map, hill shading layer or contour lines can be generated in GIS software. In fact, this model is a digital surface model (DSM), and contains every object on the Earth surface, including human built objects, forests. To decrease the elevation-differences between the real ground and the SRTM model, the ACE2 model was generated from SRTM in 2007. This derived DEM concentrated mostly on the rainforests, rivers and lakes, which were eliminated from ACE2. Forests in the temperate climate lowlands and flood basins, however, remained. The average height of these forests is 4-12 meters, and the main problem is, that they look like small hills. When making a hypsometric map or generating contours from ACE2, these small “hills” can be seen on the map. Therefore it would be worth to eliminate the effects of these forests. The authors used the land cover data of the CORINE 2000 database. Forest polygons in this dataset are correlated almost perfectly with the unwanted “hills” in ACE2. A buffer zone was made around each polygon. A program, written in Python using GDAL/OGR module, computes the average height in the buffer zone and in the polygon. If the difference between the two numbers is bigger than the tolerance (the minimum height of the forest), the elevation in every grid point of the polygon was replaced with the average height in the buffer zone. To evaluate the results the contour lines generated from ACE2 were compared to the civil Hungarian National Map System (EOTR).
Keywords
Correcting DEM; estimation of elevations; CORINE