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Accounting for uncertainty in DEMs from repeat topographic surveys: improved sediment budgets

Wheaton, Joseph, Brasington, James, Darby, S.E. and Sear, David (2010) Accounting for uncertainty in DEMs from repeat topographic surveys: improved sediment budgets Earth Surface Processes and Landforms, 35, (2), pp. 135-156. (doi:10.1002/esp.1886).

Record type: Article

Abstract

Repeat topographic surveys are increasingly becoming more affordable, and possible at higher spatial resolutions and over greater spatial extents. Digital elevation models (DEMs) built from such surveys can be used to produce DEM of Difference (DoD) maps and estimate the net change in storage terms for morphological sediment budgets. While these products are extremely useful for monitoring and geomorphic interpretation, data and model uncertainties render them prone to misinterpretation. Two new methods are presented, which allow for more robust and spatially variable estimation of DEM uncertainties and propagate these forward to evaluate the consequences for estimates of geomorphic change. The first relies on a fuzzy inference system to estimate the spatial variability of elevation uncertainty in individual DEMs while the second approach modifies this estimate on the basis of the spatial coherence of erosion and deposition units. Both techniques allow for probabilistic representation of uncertainty on a cell-by-cell basis and thresholding of the sediment budget at a user-specified confidence interval. The application of these new techniques is illustrated with 5 years of high resolution survey data from a 1 km long braided reach of the River Feshie in the Highlands of Scotland. The reach was found to be consistently degradational, with between 570 and 1970 m3 of net erosion per annum, despite the fact that spatially, deposition covered more surface area than erosion. In the two wetter periods with extensive braid-plain inundation, the uncertainty analysis thresholded at a 95% confidence interval resulted in a larger percentage (57% for 2004-2005 and 59% for 2006-2007) of volumetric change being excluded from the budget than the drier years (24% for 2003-2004 and 31% for 2005-2006). For these data, the new uncertainty analysis is generally more conservative volumetrically than a standard spatially-uniform minimum level of detection analysis, but also produces more plausible and physically meaningful results. The tools are packaged in a wizard-driven Matlab software application available for download with this paper, and can be calibrated and extended for application to any topographic point cloud (x,y,z).

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More information

Submitted date: 22 September 2008
e-pub ahead of print date: 10 December 2009
Published date: 25 February 2010
Keywords: DEM of Difference (DoD) • fluvial geomorphology • morphological method • morphological sediment budgeting • River Feshie • fuzzy inference system
Organisations: Environmental Processes & Change

Identifiers

Local EPrints ID: 73190
URI: http://eprints.soton.ac.uk/id/eprint/73190
ISSN: 0197-9337
PURE UUID: 24ef782f-6bdb-4b7b-ae98-f19a3c4d61e7
ORCID for S.E. Darby: ORCID iD orcid.org/0000-0001-8778-4394
ORCID for David Sear: ORCID iD orcid.org/0000-0003-0191-6179

Catalogue record

Date deposited: 03 Mar 2010
Last modified: 18 Jul 2017 23:51

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Contributors

Author: Joseph Wheaton
Author: James Brasington
Author: S.E. Darby ORCID iD
Author: David Sear ORCID iD

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