TY - JOUR
T1 - The effects of topographic surveying technique and data resolution on the detection and interpretation of geomorphic change
AU - Kasprak, Alan
AU - Bransky, Nathaniel D.
AU - Sankey, Joel B.
AU - Caster, Joshua
AU - Sankey, Temuulen T.
N1 - Funding Information:
This study was supported by the U.S. Department of the Interior's Bureau of Reclamation through the Glen Canyon Dam Adaptive Management Program. We thank Amy East, Helen Fairley, Brian Collins, Skye Corbett, Grand Canyon river guides, students at Grand Canyon Youth, and the many other surveyors and geomorphologists who assisted in topographic data collection in Grand Canyon. Keith Kohl, Joe Hazel, Matt Kaplinski, and Paul Grams provided insight regarding survey control operations along the Colorado River. Grand Canyon National Park (GCNP) provided data collection permits, and in particular we thank Jennifer Dierker from GCNP for guidance in the field. We thank Tom Gushue and Terry Arundel (USGS) for data archiving support. The comments of two anonymous reviewers and input from Rebecca Rossi (Dartmouth College) greatly improved this manuscript. NDB was additionally supported by a NASA Space Grant Award. AK was additionally supported by a U.S. Geological Survey Mendenhall Postdoctoral Fellowship and a Synthesis Postdoctoral Fellowship via the National Science Foundation, through the University of Minnesota's National Center for Earth Surface Dynamics. This manuscript is submitted for publication with the understanding that the U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Data used in this manuscript can be obtained by contacting the authors directly.
Publisher Copyright:
© 2019
PY - 2019/5/15
Y1 - 2019/5/15
N2 - Change detection of high resolution topographic data is commonly used in river valleys to quantify reach- and site-scale sediment budgets by estimating the erosion/deposition volume, and to interpret the geomorphic processes driving erosion and deposition. Field survey data are typically collected as point clouds that are often converted to gridded raster datasets and the ultimate choice of grid resolution is left to the user. This choice may have important implications for both the quantification and interpretation of geomorphic change. Here we used concurrent topographic data collected by terrestrial laser scanning (TLS) and structure-from-motion (SfM) photogrammetry to quantify the influence of grid resolution and sampling technique on (a) the sediment budget and (b) the presence and role of geomorphic processes (i.e., alluvial, colluvial, aeolian, and fluvial transport) driving topographic change at four sites along the Colorado River in Grand Canyon, Arizona, USA. We found that while both techniques produced similar estimates for site-scale sediment budgets, the magnitude of detected topographic change was dampened at coarser pixel resolutions. An overall decrease in the areal extent of erosion and deposition were observed, respectively, when coarsening pixel size from 5 cm to 1 m among all sites. Coarser resolution data tended to affect interpretation of landscape change along the margins of river valleys. For example, when changing from 5 cm to 1 m pixel resolution, the inferred contribution of aeolian changes to total site-scale geomorphic change increased in area by 7.9%, whereas the inferred contribution of alluvial and colluvial processes decreased in area by 97.9% and 88.2%, respectively. More generally, we found that coarsening pixel sizes disproportionately attributed geomorphic change to one or more of the most common processes operating at a site. We also found that coarsening pixel resolution amplified the net sediment imbalance at the site scale, driving the imbalance at erosional sites further into erosion and vice versa for depositional sites. Our results have implications both for point cloud data collection and for raster dataset processing. We argue that selecting the finest obtainable resolution is not always warranted to accurately quantify and interpret geomorphic change, because remote sensing technique, topographic data resolution, and analysis procedure can be optimized to capture the spatial scale of those processes driving landscape change. However, in landscapes at or near sediment equilibrium (i.e., equal amounts of erosion and deposition), the finest obtainable topographic data resolution is warranted to avoid amplifying sediment imbalance and erroneously inferring that sites are trending toward erosion or deposition.
AB - Change detection of high resolution topographic data is commonly used in river valleys to quantify reach- and site-scale sediment budgets by estimating the erosion/deposition volume, and to interpret the geomorphic processes driving erosion and deposition. Field survey data are typically collected as point clouds that are often converted to gridded raster datasets and the ultimate choice of grid resolution is left to the user. This choice may have important implications for both the quantification and interpretation of geomorphic change. Here we used concurrent topographic data collected by terrestrial laser scanning (TLS) and structure-from-motion (SfM) photogrammetry to quantify the influence of grid resolution and sampling technique on (a) the sediment budget and (b) the presence and role of geomorphic processes (i.e., alluvial, colluvial, aeolian, and fluvial transport) driving topographic change at four sites along the Colorado River in Grand Canyon, Arizona, USA. We found that while both techniques produced similar estimates for site-scale sediment budgets, the magnitude of detected topographic change was dampened at coarser pixel resolutions. An overall decrease in the areal extent of erosion and deposition were observed, respectively, when coarsening pixel size from 5 cm to 1 m among all sites. Coarser resolution data tended to affect interpretation of landscape change along the margins of river valleys. For example, when changing from 5 cm to 1 m pixel resolution, the inferred contribution of aeolian changes to total site-scale geomorphic change increased in area by 7.9%, whereas the inferred contribution of alluvial and colluvial processes decreased in area by 97.9% and 88.2%, respectively. More generally, we found that coarsening pixel sizes disproportionately attributed geomorphic change to one or more of the most common processes operating at a site. We also found that coarsening pixel resolution amplified the net sediment imbalance at the site scale, driving the imbalance at erosional sites further into erosion and vice versa for depositional sites. Our results have implications both for point cloud data collection and for raster dataset processing. We argue that selecting the finest obtainable resolution is not always warranted to accurately quantify and interpret geomorphic change, because remote sensing technique, topographic data resolution, and analysis procedure can be optimized to capture the spatial scale of those processes driving landscape change. However, in landscapes at or near sediment equilibrium (i.e., equal amounts of erosion and deposition), the finest obtainable topographic data resolution is warranted to avoid amplifying sediment imbalance and erroneously inferring that sites are trending toward erosion or deposition.
KW - Aeolian geomorphology
KW - Digital elevation model
KW - Fluvial geomorphology
KW - Geomorphic change detection
KW - Lidar
KW - Structure from motion photogrammetry
KW - Terrestrial laser scanning
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U2 - 10.1016/j.geomorph.2019.02.020
DO - 10.1016/j.geomorph.2019.02.020
M3 - Article
AN - SCOPUS:85062236665
SN - 0169-555X
VL - 333
SP - 1
EP - 15
JO - Geomorphology
JF - Geomorphology
ER -