Abstract
Microtopographic variability in peatlands has a strong influence on greenhouse gas fluxes, but we lack the ability to characterize terrain in these environments efficiently over large areas. To address this, we assessed the capacity of photogrammetric data acquired from an unmanned aerial vehicle (UAV or drone) to reproduce ground elevations measured in the field. In particular, we set out to evaluate the role of (i) vegetation/surface complexity and (ii) supplementary LiDAR data on results. We compared remote-sensing observations to reference measurements acquired with survey grade GPS equipment at 678 sample points, distributed across a 61-hectare treed bog in northwestern Alberta, Canada. UAV photogrammetric data were found to capture elevation with accuracies, by root mean squares error, ranging from 14–42 cm, depending on the state of vegetation/surface complexity. We judge the technology to perform well under all but the most-complex conditions, where ground visibility is hindered by thick vegetation. Supplementary LiDAR data did not improve results significantly, nor did it perform well as a stand-alone technology at the low densities typically available to researchers.
Highlights
Fine-scale variability in elevation, commonly referred to as microtopography, is an important factor in the distribution of greenhouse gas (GHG) flux across peatland ecosystems [1,2,3,4,5,6,7]
Sparsely vegetated hills interspersed with olive orchards, the authors reported vertical root mean squares error (RMSE) values of 21 cm compared to ground control points (GCPs)
There was no statistically significant difference (F(1, 625) = 0.130, p = 0.718) between the overall results obtained by unmanned aerial vehicles (UAVs) photogrammetry, and the ‘enhanced’ UAV photogrammetry
Summary
Fine-scale variability in elevation, commonly referred to as microtopography, is an important factor in the distribution of greenhouse gas (GHG) flux across peatland ecosystems [1,2,3,4,5,6,7]. Microtopographic data are acquired via terrestrial surveys using real-time kinematic global navigation satellite system (RTK GNSS) equipment, which are capable of centimeter accuracies [12,13]. Researchers have used photogrammetric data from unmanned aerial vehicles (UAVs) to acquire detailed microtopographic data in a variety of terrestrial settings, suggesting that the technology might provide an attractive alternative to traditional ground surveys in peatlands. Roosevelt et al [13] found UAV photogrammetry to be one order of magnitude more labor-efficient and at least two orders of magnitude more detailed (in terms of data density) than RTK GNSS surveys for microtopographic archaeology surveys in western Turkey. Lucieer et al [15] reported even better RMSE accuracies of 4 cm in microtopographic surveys of East Antarctic moss beds with UAV photogrammetry
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