Global Positioning System Sampling Intensity and Pattern Effects on Computed Topographic Attributes
- John P. Wilson ,
- Damian J. Spangrud,
- Gerald A. Nielsen,
- Jeffrey S. Jacobsen and
- David A. Tyler
Dep. of Geography, Univ. of Southern California, Los Angeles, CA 90089
Environmental Systems Research Inst., 380 New York St., Redlands, CA 92373
Dep. of Plant, Soil, and Environmental Sciences, Montana State Univ., Bozeman, MT 59717
Ashtech Agriculture Division, 90 West Central Ave., Belgrade, MT 59714
Global positioning system (GPS) and digital elevation model (DEM) technologies can provide measurements of terrain attributes that influence soil processes, soil properties, and site-specific management. We hypothesized that the intensity and pattern of sampling points affects the computed contour maps and topographic attributes. The intensity and pattern of sampling points, selected from 6284 GPS-derived x, y, z values, were varied to test this hypothesis on estimated elevations and topographic attributes in a 20-ha Montana farm field. Variations of 0.05% in mean elevation between the sample and reference grids generated ≤25% differences in slope gradients, ≤38% in specific catchment area, and ≤22% in steady-state topographic wetness index. Errors diminished as sample size (resolution) and distribution (spread) increased. Overall, the results demonstrate how relatively small differences in elevations at individual points (locations) in a landscape may mask large variations in the resultant shapes and hydrologically important topographic attributes calculated from DEMs. The intensive sampling may be practical where vehiclemounted GPS can traverse cultivated fields, but impractical in trees and rough terrain.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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