Drone flight at Baynesfield Estate
Prof Paul Davidson from the University of Illinois (USA) accompanied his students on their bi-annual visit to UKZN in Pietermaritzburg. The US students help local agricultural engineering students with their 4th year design projects. This year, Paul brought along a GoPro drone purchased from Amazon for US$1300, together with other useful accessories (e.g. 2nd battery pack). Locally, the drone (model Karma) costs about R15 000-00 (excluding accessories). The Biofuels Project Team persuaded Paul to fly the drone at Baynesfield to obtain aerial photographs of previous and current monitoring sites. Dr Gareth Lagerwall from Agricultural Engineering accompanied Paul and Richard to Baynesfield on the 3rd August.

Flying conditions on the day were perfect, with clear skies and little to no wind. The drone is housed in a convenient carrycase and takes little time to extend the arms, attach the four propellers and insert the battery (Fig. A). The drone acquired its GPS position, then launched automatically into a hover (Fig. B) and waited for further instructions. We positioned the drone to take photographs of the trial site, where soybean water use had been measured using the surface renewal technique. A small patch of crop was manually harvested in April 2017 to determine final yield (Fig. C; bare patch next to vehicle). The soybean was mechanically harvested in early May (for pig fodder) and then the site was rotated with white oats (for cattle fodder).

The photograph highlights weed growth that could not be sprayed since the micrometeorological equipment interfered with operation of the farm’s spray rig. It is also evident how the Farm Manager repositions the tractor rows each season to avoid soil compaction issues. We then flew the drone to its maximum altitude of 400 feet (~120 m) and obtained photographs showing the adequate fetch provided by the Baynesfield Farm, i.e. minimum of 100 m in all directions of uniform crop growth (image not shown). The drone was flown for approximately 20 minutes above the farm, taking photographs of the irrigation guns and other interesting farm management practices.

The drone battery was then changed and aerial photographs were taken above the current location of the surface renewal system, where actual evapotranspiration is being measured above a fallow maize field (Fig. D). The surface renewal system consists of a strongbox housing two batteries (connected in parallel), a tri-legged mast used for 2 m measurements of solar and net radiation, windspeed, air temperature as well as relative humidity. A single pole is used for the tipping bucket raingauge (1.2 m height) and two fine wire thermocouples on horizontal arms positioned at 10 cm and 100 cm above the weed-free soil surface. Wind speed is also measured at near ground level using a 2D sonic anemometer. Soil water content is monitored near the soil surface and soil temperature is measured just above two soil heat flux plates. All sensors are connected to a datalogger capable of storing high frequency measurements (10 measurements per second or 10 Hz) of air temperature via the two thermocouples. Fig. E again shows the vast fetch offered by the Baynesfield site, which is ideal of the surface renewal technique.

The drone was flown up to 1600 feet (~490 m) away from its take-off position, about half its maximum horizontal range, then landed itself at the take-off location. Interestingly, the 40 minutes of flying time generated a total of 310 Mb of hi-resolution photos and videos.


(A) GoPro Drone
(A)
(B) GoPro_Drone_Hovering
(B)
(C) Baynesfield
(C)
(D) Baynesfield thermocouples
(D)
(E) Baynesfield
(E)