Low cost Earth observation method for monitoring green house gas emissions from forests in developing countries

Abstract

Structure from Motion (SfM) from Unmanned Aerial Vehicles (UAV) is increasingly being utilised for a wide range of applications including characterisation of forests. The aim of this study was to evaluate SfM from UAVs as a potential low cost method for forest monitoring for developing countries in the context of REDD. The project evaluated SfM horizontal and vertical accuracy for measuring individual tree height. Aerial imagery was collected for two test sites; Meshaw and Dryden using a Quest QPOD UAV and DJI Phantom 2 respectively. Comparisons were made between SfM and LiDAR point clouds and surface models at the Meshaw site while at Dryden, SfM tree heights were compared to ground measured heights only. Results obtained showed a strong correlation between SfM and LiDAR digital surface models (R2=0.89) and canopy height models (R2=0.75). However a poor correlation was observed between SfM tree heights and ground measured heights (R2=0.19). The poor results at Dryden were explained by the fact that the forest plot had a closed canopy structure such that SfM failed to generate enough below-canopy ground points. The same challenges for SfM in closed canopies was also reported in other studies. Finally an evaluation of UAVs was also made to determine their usefulness and cost-effectiveness for plot-level forest monitoring. The study concluded that although SfM from UAVs performs poorly in open canopies it can still provide a low cost solution to a lot of developing countries whose forests have sparse canopy cover.