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110 In operation | Distant Imagery right parts and gas for pneumatics in the quantities needed is much harder and costlier than bulk-buying electromechanical parts such as COTS servos and motors,” Glavan adds. These, along with a proprietary motorised launcher inside the device for propelling the seeds, are key to lodging seeds at the right locations and spacing in the semi-soft ground, at a rate of about 2000 germinated seeds per load. The remaining two items of equipment were the UAV platforms that carried either the launcher or performed surveys before and after planting took place. The first UAV was a DJI M600, which was chosen for its cost-effectiveness and ease of use. The second was a custom X8 heavy-lift octocopter, built using landing gear and arms from companies including Tarot, and capable of lifting 25 kg. Initially, both systems relied heavily on DJI componentry. With the discontinuation of the M600 and many of its components, however, Distant Imagery is migrating largely to Pixhawk- based systems, including Herelink GNSSs and GCSs. “We hope CubePilot opens an office in the UAE sometime soon,” Rhodes comments. “Having an ecosystem of devices that are proven to work together removes so much stress, but local, hands-on support for the Pixhawk autopilot here is non-existent.” As mentioned, 3D printing enabled the various customisations, as well as the correct construction of the agitator, the curve of the tank housing, and the propellers. The two printers used in- house are a SeeMeCNC Rostock Max V2, and a CR10S Pro V2 from Creality. Rhodes says, “Without additive printing we would not have been able to do this. All the changes and improvements we made to the various pieces of the rigging’s housing, agitator and mounts in CAD would have taken so long and cost so much more to do using CNC machining or injection moulding.” Before reforesting Before the seed distribution begins, two additional UAVs – a DJI Phantom 4 Pro and a Mavic 2 – evaluate the environmental conditions on the ground and under the water, investigate spatial arrangements of mangroves, and geo- map the site. Before that though, Rhodes and Glavan note that considerable manual work was needed to select a site, with close-up measurement of metrics such as soil quality and elevations, as well as water depths, quality and currents, and wherever parts of the UAV survey data had to be verified. After that, the two small consumer UAVs from DJI were used to produce an orthographic model of the lagoon, with measurements of parameters that are key to the success of the planting. One of these was the geographical contours of soil inside the lagoon, as tiny variations (often within just 10 cm) of slopes and elevations play a major role in giving each seed the highest probability for long-term growth. The flight path for planting would therefore follow these contours, rather than the traditional back-and-forth paths that UAV surveys often take. Another was the prevalence of healthy mangroves, whose roots and branches provide critical protection for seedlings, so EO and normalised difference vegetation index (NDVI) camera data were vital here. The latter in particular provided evidence of any stress among the mangroves, informing the team during planning as to which areas might not see seedlings flourish. Lastly, measurement of tidal levels across shores and mangrove roots was important as these would influence where the seeds would have the highest success rates. To produce an accurate orthomosaic map, custom ground control points (GCPs) were made from corrugated plastic and distributed manually across the lagoon to aid in stitching the UAVs’ aerial photographs together. However, the team’s recent adoption of Herelink’s RTK-GNSS and Emlid’s Reach RS+ means future operations will probably use solely RTK processing and a base station rover for centimetre-accurate georeferencing and map creation for planning flights, without having to disturb areas with the GCPs. As Rhodes recounts, “We flew quite low, and that gave us about 2.5 cm April/May 2022 | Unmanned Systems Technology The operation was carried out using a DJI M600 and a custom heavy-lift X8 octocopter, both equipped with the company’s custom seed-dropping payloads