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GIS‐evaluation of two slope‐calculation methods regarding their suitability in slope analysis using high‐precision LiDAR digital elevation models
Author(s) -
Ashraf M. Irfan,
Zhao Zhengyong,
Bourque Charles P.A.,
Meng FanRui
Publication year - 2011
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.8195
Subject(s) - digital elevation model , lidar , watershed , terrain , elevation (ballistics) , remote sensing , geology , topographic wetness index , photogrammetry , streams , erosion , hydrology (agriculture) , environmental science , geomorphology , geometry , geography , cartography , mathematics , computer science , geotechnical engineering , computer network , machine learning
Slope is a metric that is essential to describe surface hydrological processes, including overland flow, soil erosion, and sediment transport. Most commercial GIS have built‐in functions to calculate the slope from Digital Elevation Models (DEMs) by means of average neighbourhood methods that are appropriate for coarse‐resolution DEMs. Emergence of high‐resolution DEMs from LiDAR data creates a need to re‐assess the suitability of existing algorithms for calculating slope in hydrological applications. In this study, we investigate the properties of two different slope‐calculation methods: an average‐neighbourhood‐slope (ANS) and a downhill‐slope (DHS) method. Conceptually, the DHS method provides a more intuitive description of surface water‐flow characteristics in an uneven terrain. DEMs of five different types were used to evaluate the methods, namely a 1‐m and 10‐m resolution DEM interpolated from irregular elevation point‐data generated with conventional photogrammetric techniques, and a 1‐m, 5‐m, and 10‐m resolution DEM derived from LiDAR data. The slopes calculated were summarized for the entire watershed, along mapped streams, and within pre‐defined ‘stream buffers’. Slopes generated for the entire watershed with 1‐m resolution LiDAR DEM indicated that the ANS method on an average produced smaller slopes than the DHS method (0·64°). A similar trend was observed in stream buffers, with greatest slope differences (Δ S ) between methods within 20‐m buffers, when the 1‐m LiDAR‐based DEM was used (Δ S = 1·12°). In contrast, the ANS‐calculated slopes along mapped streams were generally larger than those calculated with the DHS method for LiDAR‐based DEMs (Δ S = 0·81°). The results from this study signal the need for caution when estimating slopes along streams from high‐accuracy, LiDAR‐generated DEMs. Copyright © 2011 John Wiley & Sons, Ltd.