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United States Department of Agriculture

Agricultural Research Service

Research Project: INTEGRATED ASSESSMENT AND ANALYSIS OF PHYSICAL LANDSCAPE PROCESSES THAT IMPACT THE QUALITY AND MANAGEMENT OF AGRICULTURAL WATERSHEDS Title: Effect of terrestrial LiDAR point sampling density in ephemeral gully characterization

Authors
item Momm, Henrique
item Bingner, Ronald
item Wells, Robert
item Dabney, Seth
item Frees, Lyle -

Submitted to: Open Journal of Modern Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 9, 2012
Publication Date: January 31, 2013
Citation: Momm, H.G., Bingner, R.L., Wells, R.R., Dabney, S.M., Frees, L.D. 2013. Effect of terrestrial LiDAR point sampling density in ephemeral gully characterization. Open Journal of Modern Hydrology. 3:38-49.

Interpretive Summary: Sediment is a major pollutant from agricultural landscapes that originates from many sources. A significant source of sediment is produced from eroding gullies, which is also difficult to assess and differentiate from other sources. Accurate and detailed topographic information from gully surveys can provide critical information when understanding and assessing the impact of gully erosion control practices. Existing technologies to measure topography can range from land-based surveys to airborne LIght Detection and Ranging (LIDAR) systems. These systems are capable of collecting topographic information with a wide range of ground point sampling densities, but may not be detailed enough to capture gully information. New technologies, such as ground-based LIDAR systems are capable of increasing the point sampling density of field surveys, thus, increasing topographic information needed for gully studies, but also increasing the complexity of data analysis. In this study, the effect of point sampling density was investigated at individual gully scales. Overall guiding principles were developed for multi-temporal gully surveys based on various levels of ground-based LIDAR sampling points and relief variation (low, moderate, and high). For each level considered, an analysis of the full dataset was compared to reduced datasets. Results indicated a point sampling density threshold that produces little or no additional topographic information when exceeded. A reduced dataset was created using the density thresholds and compared to the original dataset with no major discrepancy. Although variations in relief can lead to different sampling requirements, the outcome of this study serves as guidance for future field surveys of gully evolution and erosion. Improved characterization of gullies provides action agencies with information critical to developing effective conservation management practices.

Technical Abstract: Gully erosion produces significant amounts of sediment from agricultural landscapes, but is difficult to monitor and quantify with existing technology. Scientific investigations of gullies depend on accurate and detailed topographic information to understand and evaluate the complex interactions between field topography and gully evolution. Detailed terrain representations can be produced by new technologies such as ground-based LIDAR systems. These systems are capable of collecting information with a wide range of ground point densities as a result of operator controlled factors such as the area of data collection (scan angle), average point density of scans, and degree of overlap between scans. Increasing the point density results in more time needed to complete field surveys with more information resulting in increased complexity of data post-processing. In this study, the effect of point sampling density on the capability to collect topographic information was investigated at individual gully scale. This was performed through the utilization of semivariograms to produce overall guiding principles for multi-temporal gully surveys based on various levels of laser sampling points and relief variation (low, moderate, and high). For each level considered, theoretical variograms were derived from experimental variograms to compare with varying percentages of randomly selected subsets of points. Results indicated a point sampling density threshold that produces little or no additional topographic information when exceeded. A reduced dataset was created using the density thresholds and compared to the original dataset with no major discrepancy. Although variations in relief and soil roughness can lead to different point sampling density requirements, the outcome of this study serves as guidance for future field surveys of gully evolution and erosion.

Last Modified: 10/25/2014
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