In 2020, Rocketmine (now RocketDNA) was approached by our client, whose portfolio includes an open-pit gold mine in Ghana. The client required speculative analysis of their tailings dam for safety reasons.

They tasked Rocketmine with conducting drone surveys of an Area Of Interest (AOI), the largely untouched tropical rainforest falling to the south of the mine and abutting the tailings dam. High quality aerial data was required to create a digital terrain map of the area and predictive modelling as part of the company’s ongoing commitment to impact assessment and to anticipate outcomes in the unlikely event of catastrophe, such as a dam collapse.

In this scenario, poor accessibility to the hot (40+°C), humid, densely forested area, some 65 square kilometres in size, meant that traditional data gathering methods were not viable. On-site problems were compounded by the extremely low cloud cover which often hangs above the tree canopy at around 300 metres and limits visibility.

These conditions limited surveying options. Manned aviation was ruled out due to the absence of suitable take-off and landing sites and exorbitant cost. In addition, the daily low cloud level around 200-300m made it impossible to use manned aviation LiDAR, as they operate at higher altitudes where the LiDAR can’t penetrate the clouds.

The poor weight-bearing capacity of traditional drones (which limits their ability to carry LiDAR technology) and short battery life meant surveying the area of interest would have involved hundreds of short flights and taken many months to complete the task.

And so, Rocketmine sought a solution on behalf of the client through its own extensive network of suppliers and with in-house expertise assessing the technological requirements. With the ability to fly autonomously, day or night, the latest Unmanned Aerial System (UAS) from Quantum Systems was not only the swiftest solution, but also the most economical.

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Combining skills and technology, Rocketmine deployed a drone pilot and a Trinity F90+ UAS equipped with Quantum-Systems’ Qube 240, a geomatics grade LiDAR scanner, to the mine site and completed the required mapping of the 65km2 area in just four days; flying at an average speed of 18m/per second at an altitude of 100-120 metres above ground.

After clearly identifying the mission’s objective – gathering data for a digital terrain map to plan protection measures to safeguard nearby villages and the tropical rainforest in the very unlikely event of a dam collapse – mapping of the project area commenced.

The drone’s capacity to carry the LiDAR for sixty-minute flights meant that working systematically across the target area, five flights per day over a four-day period, was sufficient to scan the entire area and immediately transmit all the necessary data to the software for processing.

The LiDAR, using three pulses which strike the tree canopy, mid-level under canopy and importantly, the ground, captured 40 points per square metre enabling the software to map topography and identify the watershed with fine-grained detail. It also captured digital orthophotos of the area of interest and contour lines with 0.5m isohypses.

The highly developed point cloud produced by LiDAR allowed for classification and development of cross-sections of ground points to reveal the shape and undulation of the terrain not previously visible. The contour maps have created the ability to predict water paths through the vast inaccessible area and, though not requested by the client, the mass of data enabled the Rocketmine team to provide flood simulations.

The level of detail made possible through this method of surveying was not only astounding in its coverage and accuracy (after 20 flights and 19.3 hours flight time, 11.1 billion points – 2.6 billion of which were ground points – were accumulated in this project), but the speed in which it was made available delivered information to the client in record time. Rocketmine can fly, land, and deliver data in 20 minutes.

The visual results provided to the client gave clear aerial views of the area of interest identifying the topography of the terrain with 2-metre and 50-centimetre contour lines and identifying the villages, communities and settlements within the area which potentially could be impacted by the waterflow path calculations emerging from Rocketmine’s findings.