Biomass Estimation Using 3D Data from Unmanned Aerial Vehicle Imagery in a Tropical Woodland

Abstract

Application of 3D data derived from images captured using unmanned aerial vehicles (UAVs) in forest biomass estimation has shown great potential in reducing costs and improving the estimates. However, such data have never been tested in miombo woodlands. UAV-based biomass estimation relies on the availability of reliable digital terrain models (DTMs). The main objective of this study was to evaluate application of 3D data derived from UAV imagery in biomass estimation and to compare impacts of DTMs generated based on different methods and parameter settings. Biomass was modeled using data acquired from 107 sample plots in a forest reserve in miombo woodlands of Malawi. The results indicated that there are no significant differences (p = 0.985) between tested DTMs except for that based on shuttle radar topography mission (SRTM). A model developed using unsupervised ground filtering based on a grid search approach, had the smallest root mean square error (RMSE) of 46.7% of a mean biomass value of 38.99 Mg·ha −1 . Amongst the independent variables, maximum canopy height (Hmax) was the most frequently selected. In addition, all models included spectral variables incorporating the three color bands red, green and blue. The study has demonstrated that UAV acquired image data can be used in biomass estimation in miombo woodlands using automatically generated DTMs.

Influence of Plot Size on Efficiency of Biomass Estimates in Inventories of Dry Tropical Forests Assisted by Photogrammetric Data from an Unmanned Aircraft System

“…2017, 9, 610 3 of 15 [32,33,[35][36][37]. It is therefore prudent for aspiring REDD+ implementation in developing countries, such as Malawi, to assess the application of UASs in forest inventories.…”

“…The forest is covered by miombo woodlands dominated by Julbernadia globiflora, Diplorhychus condylocarpon and Combretum zeyheri. For more details on the study area, see Kachamba et al [32]. …”

“…A summary of flight characteristics for each flight day is presented in Table 2. The procedure described here was also applied in Kachamba et al [32]. [54] was used to generate a 3D point cloud from the acquired images.…”

“…Recent research on application of UASs over small-to-medium sized forests for biomass and volume estimation in dry tropical forests [32], boreal forests [33] and temperate forests [34] have demonstrated their potential. Unlike manned aerial platforms, application of UASs have proved to produce reliable forest biomass estimates at the small-to-medium forest scale with relatively small logistical costs and thus opens an opportunity for local adaption under the REDD+ mechanism [32,33,[35][36][37]. It is therefore prudent for aspiring REDD+ implementation in developing countries, such as Malawi, to assess the application of UASs in forest inventories.…”

Decline of N and P Uptake in the Inner Protection Zone of a Terminal Reservoir during Inter-Basin Water Transfers

“…In each quadrant, we selected 36 sample areas of 1 m × 1 m for grass or nine sample areas of 5 m × 5 m for shrubs, and the average biomass density was calculated. Forest biomass was estimated using diameter-height models [46] based on the sample trees. In this study, 39 quadrants were selected for the analysis.…”