Unmanned Systems Technology 022 | XOcean XO-450 l Radar systems l Space vehicles insight l Small Robot l BMPower FCPS l Prismatic HALE UAV l InterDrone 2018 show report l UpVision l Navigation systems

85 Unmanned Systems Technology | October/November 2018 The camera installed in the Sirius’ downward-looking payload bay was a calibrated 16 MP Panasonic GX1, set to the local time zone for accurate time-referencing, and exposure settings fixed according to the coordinates to be covered in the flight plan, as well as for the resolution and degree of overlap. “The settings were key to eliminating common photogrammetry mistakes, such as time triggers getting set to occur after an incorrect time interval, or inaccurately accounting for the wind affecting the speed of the UAV flight,” Karas explains. “That could lead to aerial images being too small or too large, thus missing key mapping data points.” To help with the position and orientation of the camera’s aerial imagery, and account for the considerable variations in angles and elevations throughout the mine, 21 GCPs were established across the mission area using RTK GPS in a local UTM coordinate system. Once calibrated, the GPCs were marked with fluorescent orange paint to make them more visible. As Karas notes, “Keeping the GCPs clearly marked was harder than creating them. During one mission day, there was a scheduled blast in the mines, while on another we were caught off-guard by a sudden snowfall, so we had to continually check and re-check that the GCPs were still visible for the aerial imagery.” Future missions, the company notes, will require more permanent and visible GCP markings. Flight Just as 10 days were allotted to perform three days’ worth of flights to minimise the consequences of weather-related delays, the UpVision team made sure to conduct their flights with the Sirius during two key periods of each day, when the winds in the mine’s airspace were at their lightest. The Sirius was therefore flown only in the morning between 6 and 8 am, and in the evening between 6 and 8 pm (with the long daytime of May allowing for sufficient sunlight for aerial photography at these hours). Mainly there were two flights per period, with just one – the ninth flight – taking place on the morning of the third day. In the daytime gap between these time slots, winds were observed to reach up to 72 kph (dangerously in excess of the Sirius’ aforementioned wind tolerances). Considerable quantities of dust were also carried by the winds, posing potential risks to the UAV’s image quality and motor health. The mapping took place mainly at two flight heights, about 120 and 300 m above the mine, largely because of the high elevation for the combination of these flights with overlaps of 70-80% between rows and images. The mapping therefore achieved resolutions of between 3.5 and 10 cm per pixel. While the landing sites had been painstakingly selected, hand-launching the Sirius could theoretically be conducted from anywhere, after which it would begin flying and gathering mapping imagery along its predefined routes and parameters. For seven of the nine flights, the launch took place from the same location – the flat and grassy recovery area in the western part of the mine, as it gave a visual line of sight of the entire mine, as well as of the UAV in flight. Only two take- offs were from the other launch site, in the eastern part of the mine, and each flight took on average around 35 minutes. The rate of image capture was tied directly to the Sirius’ airspeed, and this varied significantly owing to The company established 21 ground control points for the mine photogrammetry, and maintained their markings through snowfall and a controlled blast at the mine during the operations period Creating flight plans was quite difficult owing to the sheer size of the mine area, as well as the elevations and variations therein