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For a country that barely occupies 0.16% of Earth’s surface, Namibia produces a significant share of the world’s uranium – 10%. Not only does this make Namibia the fourth largest uranium producer in the world, uranium mining itself contributes to more than 10% of Namibia’s GDP. In the coming years, these percentages are only to go higher when the Husab mine reaches its full production capacity. The mine, located 50km southeast of Swakopmund, has the potential to produce 6,800 tonnes of uranium oxide per annum and contains approximately 280 million tonnes of uranium ore. This makes it Africa’s largest and the world’s second largest open pit uranium mine.
As 2017 drew to a close, the task of surveying the main pit and stockpiles of this very mine fell on Strydom & Associates’ shoulders. The company had to determine and submit volumetric measurements for the year-end audit at a high-pressure deadline – January 3.
To keep the tight deadline for the Husab mine project, Strydom & Associates needed to map a large area in a very short time, while maintaining high accuracy. Beyond the project constraints, there were environmental challenges to account for as well. The Namib desert isn’t a very friendly place to be. Indeed, its hostile climate makes Namibia the second least densely populated country in the world. The temperature and precipitation fluctuate widely and harsh desert wind – also called East Wind – can reach a speed of up to 30m/s.
Given the magnitude of the project, the tight deadline and the adverse environmental conditions, the surveyors ruled out ground-based surveying methods as these can be very time-consuming. They also rejected the idea of using manned aircraft because of accuracy limitations, the much higher costs and the same timing constraint. Aerial surveying was their best option – with a UAV, they could collect all the required data in a few hours at a fraction of the cost.
The best of both worlds
However, not every professional mapping UAV can deliver high-accuracy results while covering large areas. In the choice between fixed-wings and the multi-rotors, the latter is automatically ruled out as multi-rotors cannot cover vast areas. On the other hand, fixed-wings cannot deliver ultra-high accuracy results and have real struggles landing on the complicated terrain – they perform belly landings, which means that they basically slide on the ground causing real threat to the on-board cameras.
The surveyors thus turned to use the vertical take-off and landing (VTOL) WingtraOne UAV. The UAV takes-off and lands vertically like a multi-rotor and transitions into flying like a fixed-wing aircraft. VTOL combines the best of both worlds: as a fixed wing, the UAV can deliver large coverage, and as a multi-rotor, it can take off and land anywhere without damaging its powerful cameras.
To obtain high accuracy results with aerial surveying, the presence of ground control points and the use of a high camera resolution camera is also extremely important. The ground control points already existed in the area and so didn’t need any additional time. Thus, the surveyors used the WingtraOne UAV equipped with a powerful camera – the full-frame Sony RX1RII, which offers an ultra-high resolution of 42MP.
Measuring 15km2 in 2.5 hours
On December 31, the Strydom & Associates team set out to map the 15km2 area. Flight planning was done with WingtraOne’s custom flight planning software, the WingtraPilot. The surveyors had already outlined the area they wanted to map on WingtaPilot’s base layer map, and it had generated the required flight plans. Four flights were planned in total, each set to a ground sample distance of 5cm/px, resulting in a flight altitude of 390m.
The wind speed on the ground being 7m/s, WingtraPilot ran a host of automated safety checks before the flight, to make sure that operations could be undertaken safely. This and additional mission planning features on the app also let the surveyors from Strydom & Associates make minor adjustments to the flight plans and fly a completely hands-off safe operation.
For each flight, the drone took-off from the ground automatically, flew along the generated flight path capturing images and then landed safely on its 4m2 landing spot. In 2.5 hours of flight time, the surveyors collected aerial imagery consisting of 1,500 RGB images of the entire area. The images were georeferenced by the onboard GPS data from the WingtraOne.
The georeferenced images were later post-processed by the Agisoft Photoscan software. The evenly distributed ground control points in the area helped to optimise camera positions and orientation data. Then, combining this information with a comparison of many different overlapping images, highly accurate 3D models were built. At the end, the team was able to achieve down to 1cm relative accuracy, both horizontally as well as vertically, in their models – extremely important for volumetric measurements.
Meeting the demands of a challenging task
Company co-founder Hermann Strydom says: “Ease of flight planning means that small last-minute changes to the flight plans designed in the office could be easily made to meet the conditions experienced on the site. The main advantage with the WingtraOne was the high-quality images from the camera. The Sony RX1RII camera with 35mm lens makes it possible to cover the area efficiently at a high altitude of 390m.”
He adds that being armed with a powerful camera mounted on a UAV that’s efficient in flight meant that his surveyors could keep to their high-pressure deadline. Short set-up time, hands-off operation and flexible planning enabled the team to collect data in the field efficiently. The level of detail afforded by the full-frame camera meant that further analysis in the office could also be completed quickly and with high accuracy.
The mission that might have seemed impossible from the beginning went without a hitch. Strydom & Associates could keep their deadline and compile a set of very valuable data in one of the harshest environments there is.
Adyasha Dash is a software developer at Wingtra (www.wingtra.com)
