The effects of DEM resolution and neighborhood size on digital soil survey

Terrain characteristics, such as slope gradient, slope aspect, profile curvature, contour curvature computed from digital elevation model (DEM), are among the key inputs to digital soil surveys based on geographic information systems (GIS). These terrain attributes are computed over a neighborhood (spatial extent). The objective of this research was to investigate the combined effect of DEM resolution and neighborhood size on digital soil surveys using the Soil-Landscape Inference Model (SOLIM) approach. The effect of neighborhood size and DEM resolution on digital soil survey was examined through computing the required terrain attributes using different neighborhood sizes (from 3 to 54 m) for 3, 6, 9, 12, 18, and 27 m resolution DEM. These attributes were then compiled and used to digitally map soils using the SoLIM approach. Field work completed on a hillslope in Dane County, WI in the summer of 2003 was used to validate each of the SoLIM derived soil surveys for accuracy. The results of the soil survey validations suggest that there is a range of neighborhood sizes that produces the most accurate results for a given resolution DEM. This range of neighborhood sizes, however, varies from landscape to landscape. When the soils on a gently rolling landscape were mapped, the neighborhood sizes that produced the most accurate results ranged from about 33-48 m. When soils on short, steep backslope positions were mapped, the neighborhood size values that produced the most accurate results range from about 24-36 m. This paper also shows that it is not always the highest resolution DEM that produces the highest accuracy. Knowing which DEM resolution and neighborhood size combinations produce the most accurate digital soil surveys for a particular landscape will be extremely useful to users of GIS-based soil-mapping applications. (c) 2006 Elsevier B.V. All rights reserved.