5.2.3. UAV operation

Having determined one’s area of interest, established ground control points (GCPs) and defined flight parameters, one is set to fly the UAV. If the mission has been properly planned, this should be an easy affair! Below, we present some important lessons concerning UAV flights in smallholder agricultural areas in sub-Saharan Africa and Asia.

  • Permission to fly: depending on jurisdiction and the height at which you intend to fly, flight permission/clearance from the national aviation authority may be required. In Mexico, for instance, flights above 120 m (with UAVs heavier than 2 kg) require authorization from air traffic regulators. The presence of sprayer aircrafts or other low altitude flying machines needs to be taken into account.
  • Flight time: the best time to operate UAVs in high temperature areas (e.g., the sites in Mali, northern Nigeria and Tanzania) is between 9.00 am and 11.00 am. Exposure to high temperatures may cause overheating of the camera or even the whole unit. The eBee platform was found to be particularly vulnerable to high temperatures, possibly due to its black body. One way to reduce the effect of heating is to limit exposure to direct sunlight only to actual flight time. Use of an umbrella or other means of sun shield can be effective. One may also consider covering the black UAV body parts with a material that reduces its susceptibility to heating. This practice, however, may impact device warranty.
  • Batteries: It is adviced practice not to completely exhaust batteries during flight campaigns. For the eBee, there is an 80% battery usage limit which when adhered to can prolong battery life. It is advisable to factor this into one’s planning.  Generally, the battery charging strategy as suggested by the manufacturer should be adhered to.
  • UAV operations may draw a spectator crowd, often including children of all ages.  Operation  safety procedures should factor in the safety of the crowd, and the pilot should weigh fully the risks of this type before starting flight.
  • Certain bird species, such as raptors or those with a nest nearby, may attack the UAV; likewise, dogs may grow an interest in a UAV taking off or landing.
  • It is important to clear SD cards before each flight campaign, and extract images after each flight mission.
  • Mounted cameras sometimes switch to video mode as a result of the UAV shaking during take-off or landing, or in strong windy conditions. It is, therefore, important to ensure that the camera is firmly fixed to record only still pictures.
  • Skies with scattered clouds bring scattered cloud shadows on the land, and this often brings problems of subsequent image use and analysis.  Especially when winds are high, the movement of clouds will cause additional problems of mosaicking.
  • Flying is preferred during the morning because wind speeds are often higher in the afternoon and cloud cover is also increased.
  • Flying around the time of solar noon should be avoided because of specular reflection from the land surface, especially from wet areas, such as flooded rice fields but also from other land cover types.