Imperial College London
Portrait Picture

Dr Alex Whittaker

Faculty of Engineering, Department of Earth Science & Engineering

Reader in Landscape Dynamics
 
 
 
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Contact

 

+44 (0)20 7594 7491a.whittaker Website

 
 
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Location

 

3.51Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Citation

BibTex format

@article{Mair:2022:10.5194/esurf-10-953-2022,
author = {Mair, D and Do, Prado AH and Garefalakis, P and Lechmann, A and Whittaker, A and Schlunegger, F},
doi = {10.5194/esurf-10-953-2022},
journal = {Earth Surface Dynamics},
pages = {953--973},
title = {Grain size of fluvial gravel bars from close-range UAV imagery - uncertainty in segmentation-based data},
url = {http://dx.doi.org/10.5194/esurf-10-953-2022},
volume = {10},
year = {2022}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - Data on grain sizes of pebbles in gravel-bed rivers are of key importance for the understanding of river systems. To gather these data efficiently, low-cost UAV (uncrewed aerial vehicle) platforms have been used to collect images along rivers. Several methods to extract pebble size data from such UAV imagery have been proposed. Yet, despite the availability of information on the precision and accuracy of UAV surveys as well as knowledge of errors from image-based grain size measurements, open questions on how uncertainties influence the resulting grain size distributions still persist. Here we present the results of three close-range UAV surveys conducted along Swiss gravel-bed rivers with a consumer-grade UAV. We measure grain sizes on these images by segmenting grains, and we assess the dependency of the results and their uncertainties on the photogrammetric models. We employ a combined bootstrapping and Monte Carlo (MC) modeling approach to model percentile uncertainties while including uncertainty quantities from the photogrammetric model. Our results show that uncertainty in the grain size dataset is controlled by counting statistics, the selected processed image format, and the way the images are segmented. Therefore, our results highlight that grain size data are more precise and accurate, and largely independent of the quality of the photogrammetric model, if the data are extracted from single, undistorted nadir images in opposition to orthophoto mosaics. In addition, they reveal that environmental conditions (e.g., exposure to light), which control the quality of the photogrammetric model, also influence the detection of grains during image segmentation, which can lead to a higher uncertainty in the grain size dataset. Generally, these results indicate that even relatively imprecise and inaccurate UAV imagery can yield acceptable grain size data, under the conditions that the photogrammetric alignment was successful and that suitable image formats were sele
AU  - Mair,D
AU  - Do,Prado AH
AU  - Garefalakis,P
AU  - Lechmann,A
AU  - Whittaker,A
AU  - Schlunegger,F
DO  - 10.5194/esurf-10-953-2022
EP  - 973
PY  - 2022///
SN  - 2196-6311
SP  - 953
TI  - Grain size of fluvial gravel bars from close-range UAV imagery - uncertainty in segmentation-based data
T2  - Earth Surface Dynamics
UR  - http://dx.doi.org/10.5194/esurf-10-953-2022
VL  - 10
ER  -
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