Extra tight deadlines, harsh weather conditions and the biggest Uranium mine in Africa in sight – these were the project conditions that met Strydom & Associates in the Namib Desert. Luckily, with the help of a UAV, surveyors were able to successfully perform a mine surveying task and conduct the needed volumetric measurement over a 15 sq. km. open pit mine in a single day.

For a country that barely occupies 0.16% of Earth’s surface, Namibia produces a significant share of world’s Uranium – 10%. Not only does this make Namibia the 4th largest Uranium producer in the world (World Uranium Mining, 2016), Uranium mining itself contributes to more than 10% of Namibia’s GDP. In the coming years, these percentages are only to go higher with the Husab mine reaching its full production capacity. The mine, located 50 km south-east of Swakopmund, has the potential to produce 15 million pounds (6800 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 the year 2017 drew to a close, the task of the stockpile and main mine surveying  fell on Strydom & Associates’ shoulders. The company had to determine and submit volumetric measurements for the year end audit at a high pressure deadline – 3rd of January.

Strydom & Associates is no stranger to challenging tasks – with a multidisciplinary approach, they have completed diverse projects ranging from a topographical survey of 0.5 Ha to an aerial survey of 10 000 Ha, with their clients spread all over the Southern Africa. However, 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.

Satisfying the constraints

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 that second least densely populated country in the world. The temperature and precipitation fluctuates widely and harsh desert wind – also called East Wind – can reach a speed of up to 30 m/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 aircrafts because of accuracy limitations, much higher costs and the very same timing constraint. Aerial mine surveying was their best option — with a UAV, they could collect all the required data in a matter of few hours at a fraction of the cost.

However, not every professional mapping UAV can deliver high accuracy results while covering large areas. In the choice between fixed-wings and the multirotors, the latter one gets automatically ruled out as multirotors cannot cover vast areas. On the other hand, fixed wings cannot deliver ultra-high accuracy results and have significant struggles landing on the complicated terrain – they perform belly landings, which means that they basically slide on the ground causing real threat to the onboard cameras.

The surveyors thus turned to use the VTOL (vertical take-off and landing) WingtraOne UAV. The UAV takes-off and lands vertically like a multirotor and transitions into flying like a fixed-wing aircraft. VTOL combines best of both worlds: as a fixed wing, WingtraOne can deliver large coverage, and as a multirotor, it can take off and land anywhere without damaging its powerful cameras.

To obtain high accuracy results with aerial mine 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 ultra high resolution of 42MP.

Measuring 15 sq. km. in 2.5 hour flight time

On 31st December, equipped with a WingtraOne UAV, the Strydom & Associates team set out to map the area of 1500 Ha or 15 km2. 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. 4 flights were planned in total, each one set to a GSD of 5 cm/px resulting in a flight altitude of 390 m.

It was a windy day on the field with the wind on ground being 7 m/s. WingtraPilot ran a host of automated safety checks before the flight, to make sure that operations will be undertaken safely. This and additional mission planning features on the app also let the surveyors from Strydom & Associates to make minor adjustments to the flight plans and allow 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 4 m2 landing spot. In 2.5 hours of flight time, the surveyors collected aerial imagery consisting of 1500 RGB images of the entire 15 km2 area. The images were georeferenced by the onboard GPS data from the WingtraOne.

The georeferenced images were later post-processed by the Agisoft Photoscan and Pix4D softwares. The evenly distributed ground control points in the area helped to optimize camera positions and orientation data. Then, combining this information with a comparison of many different overlapping images, highly accurate 3D models were built.

Herman Strydom described the aerial images: “In the Digital Elevation Model (DEM), clearly visible are one of the main pits, and some stockpiles. If you look just above the deepest area of the (shaded blue) you will notice the little dimples caused by the blast holes drilled – indication of the high degree of detail.”

Meeting the demands of a challenging task

“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. Sony RX1RII camera with 35 mm lens makes it possible to cover the area efficiently at a high altitude of 390 m,” adds Hermann Strydom.

According to him, being armed with a powerful camera mounted on a UAV that’s efficient in flight meant that Strydom & Associates land surveyors could keep to their high pressure deadline. Low set up time, hands-off operation and flexible planning allowed the team to complete their task of data collection on 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.

Mission (im)possible

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 over one of the harshest environments there is. The WingtraOne VTOL UAV appeared to be the reliable choice that helped the surveyors’ team to conduct an end of the year audit survey of the Husab mine over the leap from 2017 to 2018.

(Author: Adyasha Dash, Source: Wingtra.com)