Assessment of Forest Structure Using Two UAV Techniques: A Comparison of Airborne Laser Scanning and Structure from Motion (SfM) Point Clouds
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School of Land and Food, University of Tasmania, Hobart, TAS 7001, Australia
2
School of Mathematics and Geospatial Science, RMIT University, Melbourne, VIC 3000, Australia
3
Biospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
4
Department of Forest Management, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences in Prague, Praha 6, Czech Republic
*
Author to whom correspondence should be addressed.
Academic Editors: Juha Hyyppä, Xinlian Liang and Eetu Puttonen
Forests 2016, 7(3), 62; https://doi.org/10.3390/f7030062
Received: 12 January 2016 / Revised: 29 February 2016 / Accepted: 3 March 2016 / Published: 7 March 2016
(This article belongs to the Special Issue Forest Ground Observations through Terrestrial Point Clouds)
This study investigates the potential of unmanned aerial vehicles (UAVs) to measure and monitor structural properties of forests. Two remote sensing techniques, airborne laser scanning (ALS) and structure from motion (SfM) were tested to capture three-dimensional structural information from a small multi-rotor UAV platform. A case study is presented through the analysis of data collected from a 30 × 50 m plot in a dry sclerophyll eucalypt forest with a spatially varying canopy cover. The study provides an insight into the capabilities of both technologies for assessing absolute terrain height, the horizontal and vertical distribution of forest canopy elements, and information related to individual trees. Results indicate that both techniques are capable of providing information that can be used to describe the terrain surface and canopy properties in areas of relatively low canopy closure. However, the SfM photogrammetric technique underperformed ALS in capturing the terrain surface under increasingly denser canopy cover, resulting in point density of less than 1 ground point per m2 and mean difference from ALS terrain surface of 0.12 m. This shortcoming caused errors that were propagated into the estimation of canopy properties, including the individual tree height (root mean square error of 0.92 m for ALS and 1.30 m for SfM). Differences were also seen in the estimates of canopy cover derived from the SfM (50%) and ALS (63%) pointclouds. Although ALS is capable of providing more accurate estimates of the vertical structure of forests across the larger range of canopy densities found in this study, SfM was still found to be an adequate low-cost alternative for surveying of forest stands.
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Keywords:
unmanned aerial vehicle (UAV); LIDAR airborne laser scanning; structure from motion; digital terrain model; forest structure; canopy cover; tree height
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MDPI and ACS Style
Wallace, L.; Lucieer, A.; Malenovský, Z.; Turner, D.; Vopěnka, P. Assessment of Forest Structure Using Two UAV Techniques: A Comparison of Airborne Laser Scanning and Structure from Motion (SfM) Point Clouds. Forests 2016, 7, 62.
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