Charcoal heaps volume estimation based on unmanned aerial vehicles

The charcoal stock in a forestry business is controlled based on the theoretical capacity of the masonry ovens (input) and shipped trucks (output). During the year, the company must monitor the stock for accountability reports and internal governance. This paper proposes a more efficient and precise survey method that overcomes the challenges of the common monitoring system in Brazil. In this study, a monitoring method based on digital stereoscopy from UAV images was implemented and evaluated. The results were compared with those of the traditional topographic survey based on RTK equipment. A multi-engine UAV, with an integrated global navigation satellite system (GNSS) and real-time kinematic positioning (RTK) equipment was used to fly over and survey a masonry oven complex containing eight charcoal heaps. Two stereoscopic processing methods were applied: (1) very low quality and (2) high quality to image alignment, reconstruction of a dense cloud, facet count and a three-dimensional mesh creation. Low-quality products showed geometric deformities when compared to high quality, but resulted in estimations similar to the topographic survey. Results indicated that the volume estimation of the charcoal heaps using UAV derived orthomosaics can replace the conventional method of GNSS RTK surveys with considerable gains in stockpile volume accuracy, inventory frequency and labour safety. The high quality processing method registered improvements in geometric precision and accuracy.