Uncertainty assessment of ephemeral gully identification, characteristics and topographic threshold when using aerial photographs in agricultural settings
[en] Manual digitizing on aerial photographs is still commonly used for characterizing gully erosion over large areas. Even when automated detection procedures are implemented, manual digitizing is frequently being resorted to in order to constitute reference datasets used for training and validation. In both cases, manual digitizing entails some subjective decisions on behalf of the operator, which introduces uncertainty into the resulting datasets. To assess the magnitude of this uncertainty, 11 experienced operators were asked to digitize and classify ephemeral gullies (EGs) on cropland following a standardized methodology. The resulting 11 datasets were compared in terms of number, type and location of EGs. Furthermore, for EGs located on a welldefined runoff flow concentration axis, the slope versus contributing area topographic thresholds required for initiating gully channels were assessed using four thresholding methods, and compared across the 11 datasets. The operators identified 259 different EGs. However, the number (52–139) and sum total length (8.9–23.7 km) of EGs varied widely across operators. Only 34% of the EGs were digitized by more than half of the operators, and 7% were identified by all. Identification of EGs located on a well-defined flow concentration axis proved least subjective. The longer the EG and the more fields the EG crossed, the larger the number of operators that were able to identify it. EGs were also most easily identified when located in sugar beet fields as compared to other crops. EG classification and topographic threshold lines were also found to be strongly operator-dependent. Quantile regression appeared to be one of the most robust thresholding methods. Operator subjectivity when digitizing EGs on orthophotographs introduces uncertainty that should be taken into account in future remote sensing-based studies of EG erosion whenever they rely, in part or in full, on manual photograph interpretation.
Maugnard, Alexandre; Université Catholique de Louvain - UCL > Environmental Sciences > Earth and Life Institute
Cordonnier, Hélène; Service Public de Wallonie > Ressources Naturelles et Environnement (DGO3) > Direction générale opérationnelle Agriculture
Degré, Aurore ; Université de Liège - ULiège > Sciences et technologie de l'environnement > Systèmes Sol-Eau
Demarcin, Pierre ; Université de Liège - ULiège > Sciences et technologie de l'environnement > Systèmes Sol-Eau
Pineux, Nathalie ; Université de Liège - ULiège > Sciences et technologie de l'environnement > Systèmes Sol-Eau
Bielders, Charles; Université Catholique de Louvain - UCL > Environmental Sciences > Earth and Life Institute
Language :
English
Title :
Uncertainty assessment of ephemeral gully identification, characteristics and topographic threshold when using aerial photographs in agricultural settings
Publication date :
2014
Journal title :
Earth Surface Processes and Landforms
ISSN :
0197-9337
eISSN :
1096-9837
Publisher :
Wiley, Hoboken, United States - New Jersey
Peer reviewed :
Peer Reviewed verified by ORBi
Funders :
SPW DG03-DGARNE - Service Public de Wallonie. Direction Générale Opérationnelle Agriculture, Ressources naturelles et Environnement
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