Considering the safety issue in surveying an open pit-mine, some of the surveyors are not allowed to carry out land surveying on such sites. To counter this, companies have come up with a solution of conducting aerial surveys. The decision is quite constructive as it helps in getting all the vital information that was previously carried out during a land survey.
In addition to being one of the easy alternatives, Namibian Minim Survey Services (NMSS) has proved aerial surveying economical. Saving more than 95% of the mobilization cost in transporting the resources for land-based survey, the unmanned aerial system (UAS) stands out in all aspects.
After conducting extensive research in this area for a long time, NMSS has come up with the project to investigate UAS for its implementation. Choosing X100 gateway at platinum mine for the project demo, NMSS carried out observations so they could relate to the lidar survey previously carried out there.
The plan was to analyze a portion of Abenab Mine for its reuse as it had been closed since the 1960s. The mine, located west of Tsumeb, is a vanadium-lead mine owned by South West Africa Company.
The 100 hectares of survey area has a main pit of about 60 meters depth and 120 meters length. The surveyors ensure 5 cm ground separation and a height of 150 meters for perfect measurements. They constructed the ground control points (GCPs) with red colored stripes of masonite having the length of 10 meter each. Ten points were placed at specific positions and covered various spots like the top of dumps, inner pit, and leveled ground and are remotely controlled by the UTM34S coordinate system.
X100 Flight Launch
Research suggests 9 am to 3 pm to be the best time for flight. With a total flight area set to 140 hectares and favorable wind conditions assumed, the flight X100 was all set to launch.
Dave Bansemer, an NMSS team member, placed the GCPs on site, while one of his colleagues performed a static survey. Having all the GCPs set to positions by 11 am and the flight particulars being crosschecked, X100 was finally launched at 11 am. The flight suffered some turmoil at 150-meter altitude, but landed safely in around 35 minutes.
In order to process the data measured by X100, the team worked on the coordinates achieved in the process of photo-control identification and used Gateway Stretchout Pro Software. The next step was number crunching to create the orthomosaics and final point cloud. The team managed to remain in the error budget having 3 cm horizontal error and 9 cm vertical error.
After successful completion of survey, NMSS verified the point cloud with the previous survey and results seem completely accurate.
Some of the lessons that NMSS learnt are helpful for future UAV surveyors. Firstly, since the flight, the wind direction controls the flight, it is recommended to place more GCPs for accurate results. Secondly, the point size must be set according to the flight altitude. Thirdly, ensure job task completeness before leaving the area. Lastly, surveyors must consider obstacles into account while deciding landing area.