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Remote Sens. 2017, 9(11), 1187; https://doi.org/10.3390/rs9111187

Photogrammetric UAV Mapping of Terrain under Dense Coastal Vegetation: An Object-Oriented Classification Ensemble Algorithm for Classification and Terrain Correction

1
Department of Geography & Anthropology, Louisiana State University, Baton Rouge, LA 70803, USA
2
Coastal Studies Institute, Louisiana State University, Baton Rouge, LA 70803, USA
3
Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803, USA
4
School of Environment and Natural Resources, Ohio Agriculture Research and Development Center, Ohio State University, Wooster, OH 44691, USA
5
Department of Geography, Geology and Planning, Missouri State University, Springfield, MO 65897, USA
*
Author to whom correspondence should be addressed.
Received: 31 August 2017 / Revised: 9 November 2017 / Accepted: 13 November 2017 / Published: 19 November 2017
(This article belongs to the Section Remote Sensing in Agriculture and Vegetation)
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Abstract

Photogrammetric UAV sees a surge in use for high-resolution mapping, but its use to map terrain under dense vegetation cover remains challenging due to a lack of exposed ground surfaces. This paper presents a novel object-oriented classification ensemble algorithm to leverage height, texture and contextual information of UAV data to improve landscape classification and terrain estimation. Its implementation incorporates multiple heuristics, such as multi-input machine learning-based classification, object-oriented ensemble, and integration of UAV and GPS surveys for terrain correction. Experiments based on a densely vegetated wetland restoration site showed classification improvement from 83.98% to 96.12% in overall accuracy and from 0.7806 to 0.947 in kappa value. Use of standard and existing UAV terrain mapping algorithms and software produced reliable digital terrain model only over exposed bare grounds (mean error = −0.019 m and RMSE = 0.035 m) but severely overestimated the terrain by ~80% of mean vegetation height in vegetated areas. The terrain correction method successfully reduced the mean error from 0.302 m to −0.002 m (RMSE from 0.342 m to 0.177 m) in low vegetation and from 1.305 m to 0.057 m (RMSE from 1.399 m to 0.550 m) in tall vegetation. Overall, this research validated a feasible solution to integrate UAV and RTK GPS for terrain mapping in densely vegetated environments. View Full-Text
Keywords: photogrammetric UAV; high resolution; coastal topographic mapping; wetland restoration; classification correction; terrain correction; object-oriented analysis; classification ensemble photogrammetric UAV; high resolution; coastal topographic mapping; wetland restoration; classification correction; terrain correction; object-oriented analysis; classification ensemble
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Meng, X.; Shang, N.; Zhang, X.; Li, C.; Zhao, K.; Qiu, X.; Weeks, E. Photogrammetric UAV Mapping of Terrain under Dense Coastal Vegetation: An Object-Oriented Classification Ensemble Algorithm for Classification and Terrain Correction. Remote Sens. 2017, 9, 1187.

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