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ARS Home » Pacific West Area » Reno, Nevada » Great Basin Rangelands Research » Research » Publications at this Location » Publication #273954
Title: Multiscale assessment of green leaf area in a semi-arid rangeland with a small unmanned aerial vehicle

Author
item MCGWIRE, KENNETH - Desert Research Institute
item Weltz, Mark
item Finzel, Julie
item Morris, Christopher
item FENSTERMARKER, LYNN - Desert Research Institute
item MCGRAW, DAVID - Desert Research Institute

Submitted to: International Journal of Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2012
Publication Date: 11/8/2012
Citation: Mcgwire, K.C., Weltz, M.A., Finzel, J.A., Morris, C.E., Fenstermarker, L., Mcgraw, D. 2012. Multiscale assessment of green leaf area in a semi-arid rangeland with a small unmanned aerial vehicle. International Journal of Remote Sensing. 34(5):1615-1632.

Interpretive Summary: Spatial variability in green leaf cover of a sagebrush dominated site was studied by comparing field measurements on 50 m crossed transects to aerial and satellite imagery. Direct measurement of green leaf cover is the most accurate method but is labor-intensive and expensive. The normalized difference vegetation index was calculated for multiple 2 cm resolution images collected over field transects with a multispectral digital camera mounted on a radio controlled helicopter, as well as a 30 m resolution Landsat Thematic Mapper image. Variograms of green cover from these two sources show that the range of influence for spatial autocorrelation extended to a distance of approximately 200 m. As a result, field transects that are much smaller than this extent are generally within a locally correlated zone and therefore may not represent the actually represent green cover for the overall landscape. Field sampling strategies that are not of sufficient spatial extent to exceed this autocorrelation length are shown to increase variance and thereby require a greater number of sampling locations to reach a specific degree of accuracy. The time and cost of adding more spatially extensive sampling at each location may not be feasible. However by using an unmanned aerial vehicle in conjunction with field sampling it may provide the cost-efficiency necessary for developing sampling strategies for western rangelands that have high spatial variance in canopy cover.

Technical Abstract: Spatial variability in green leaf cover of a western rangeland was studied by comparing field measurements on 50 m crossed transects to aerial and satellite imagery. The normalized difference vegetation index was calculated for multiple 2 cm resolution images collected over the field transects with a multispectral digital camera mounted on a radio controlled helicopter, as well as a 30 m resolution Landsat Thematic Mapper image. Variograms of green cover from these two sources show that the range of influence for spatial autocorrelation extended to a distance of approximately 200 m. As a result, field transects that are much smaller than this extent are generally within a locally correlated zone and therefore may represent anomalies in the overall landscape. Sampling strategies that are not of sufficient spatial extent to exceed this autocorrelation length are shown to increase variance and thereby require a greater number of sampling locations to reach a given level of measurement uncertainty. The time and cost of more spatially extensive sampling at each location may be less than deploying to a larger number of locations with smaller transects, and unmanned aerial vehicles may provide a valuable role in extending current field sampling strategies for quantifying health of western shrub dominated rangelands.