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Quantifying Uncertainty of Measuring Gully Morphological Evolution with Close-Range Digital Photogrammetry

Karl R. Gesch, Robert R. Wells, Richard M. Cruse, Henrique G. Momm, Seth M. Dabney
Soil Science Society of America journal 2015 v.79 no.2 pp. 650-659
accuracy, computer software, digital elevation models, engineering, hydrology, landforms, landscapes, photogrammetry, quantitative analysis, soil science, uncertainty
Measurement of geomorphic change may be of interest to researchers and practitioners in a variety of fields, including geology, geomorphology, hydrology, engineering, and soil science. Landscapes are often represented by digital elevation models. Surface models generated of the same landscape over a time interval can be compared with estimate geomorphic evolution. Any such morphologicalestimate of change in a landform should include a range of probable values based on the quality of the digital elevation models that represent the surface of interest. This study sought to determine the uncertainty associated with detecting changes in reaches of ephemeral gullies with close-range digital photogrammetry. An experimental surface was constructed, surveyed, and photographed. The images were used as input to photogrammetry software to generate point clouds, which were then analyzed to determine the quality of elevation data generated by the photogrammetric technique. For individual point clouds the 2σ relative vertical accuracy was determined to equal 0.916 mm, and the 2σ absolute (geo-referenced) vertical accuracy was computed as 8.26 cm, and the 95% confidence range (2σ uncertainty) of detecting elevation change between two point clouds was determined to be ±1.29 to ±2.55 mm, depending on relief. These values could be applied to volumetrically derived estimates of geomorphic change as an uncertainty range. The high vertical accuracy and small uncertainty in elevation change determined in this study suggest that close-range digital photogrammetry is an effective and acceptable method to accurately detect small changes in ephemeral gullies or other geomorphic features of interest.