Abstract
Topography is a crucial surface characteristic in soil erosion modeling. Soil erosion studies use a digital elevation model (DEM) to derive the topographical characteristics of a study area. Majority of the times, a DEM is incorporated into erosion models as a given parameter and it is not tested as extensively as are the parameters related to soil, land-use and climate. This study compares erosion relevant topographical parameters—elevation, slope, aspect, LS factor—derived from 3 DEMs at original and 20 m interpolated resolution with field measurements for a 13 km2 watershed located in the Indian Lesser Himalaya. The DEMs are: a TOPO DEM generated from digitized contour lines on a 1:50,000 topographical map; a Shuttle Radar Topography Mission (SRTM) DEM at 90-m resolution; and an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) DEM at 15-m resolution. Significant differences across the DEMs were observed for all the parameters. The highest resolution ASTER DEM was found to be the poorest of all the tested DEMs as the topographical parameters derived from it differed significantly from those derived from other DEMs and field measurements. TOPO DEM, which is, theoretically more detailed, produced similar results to the coarser SRTM DEM, but failed to produce an improved representation of the watershed topography. Comparison with field measurements and mixed regression modeling proved SRTM DEM to be the most reliable among the tested DEMs for the studied watershed.
Highlights
One of the most important factors affecting soil erosion by water is topography [1]
The results showed no significant differences between TOPO and Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) whereas the as the DEM resolution increased from 15-m (ASTER) elevations were found to be significantly lower than both TOPO and SRTM DEMs (Figure 4)
The RMSE between 152 field and DEM tiles was found to be higher than 50 m for all the DEMs with the SRTM 20m and SRTM 90m showing the lowest values of 50.60 m and 52.72 m respectively (Table 1)
Summary
Digital elevation models (DEMs) have been commonly used in a geographic information system (GIS) for representing topography and for extracting topographical and hydrological features for various applications, including soil erosion studies [2]. DEMs can be generated by several techniques which include ground surveys, topographical maps, stereo photogrammetry, laser scanning and InSAR [3]. Shuttle Radar Topography Mission (SRTM) collected data in 2000 using InSAR technique which has been processed to generate DEMs with 1 arcsecond (approximately 30 m) and 3 arcsecond (approximately 90 m) spatial resolutions [4]. Radiometer (ASTER), an advanced multispectral imager launched in December 1999, has been used to generate DEMs with 15-m spatial resolution [5]. The most widely used method of obtaining a DEM, is to interpolate it from vectorized contour lines digitized from regional topographical maps
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