Drone-mounted cameras can provide high spatial resolution and fast turnaround capabilities whilst remaining relatively low-cost and easy to use when compared to satellite imagery.
Manufacturers claim that data collected from drone-mounted cameras can be used to understand nutrient levels and determine fertilizer application; plan drainage and irrigation; compile plant counts and analyse stand establishments; reduce crop damage; and detect fungi and pests.
Drone-mounted cameras are especially useful when it comes to plant inventory. Plant inventory management still mostly involves labour and time-intensive manual counting, especially for orchards and nursery fields with large areas, with those growers often counting only a portion of their crop, and inaccurately.
This is an issue shared by many tree growers, including J. Frank Schmidt and Son, a wholesale production nursery based in Oregon, USA. This business grows 500 shade and flowering tree varieties over 2500 acres, employing more than 350 full-time staff and 150 seasonal/casual workers.
Sam Doane, Production Horticulturalist at J. Frank Schmidt and Son, says that with a few million trees sold every year, even a small error percentage is more than what you would like.
Drone, camera, action!
J. Frank Schmidt and Son now fly two drones: the DJI Phantom Pro 4 and the DJI Matrice 100. The nursery uses the DJI Phantom Pro 4 mostly for marketing purposes. Sam flies the DJI Matrice 100 mounted with one of either two cameras: one in Red-Green-Blue (RGB) and the other Near Infrared-Green-Blue (NIRGB).
“One acre of a variety is a large planting for us”, Sam says, adding that he can still manually count more cheaply. Sam suggests to other growers interested in putting up drones that they “add value in the sky, start with something affordable”. For J. Frank Schmidt and Son, that means getting a return on investment with marketing images.
And now for some maths!
Once the maps are uploaded, some mathematics is required to make them meaningful. Cameras capturing Near Infrared (NIR) light can apply the Normalized Difference Vegetation Index (NDVI) and other algorithms. These algorithms compare the proportions of light captured across the different bands they register and then compute numerical values for each pixel or area of a given drone map. These maps are then assigned colors based on those numerical values, making it easier to identify between healthy and unhealthy areas.
Normalized Difference Vegetation Index (NDVI)
NDVI nominally indicates the health of green vegetation. Plants appear green to humans because chlorophyll strongly reflects NIR while red and blue are absorbed. A healthy leaf’s spongy mesophyll usually reflects most NIR. In dehydrated or stressed plants, this spongy layer collapses, meaning the leaves reflect less NIR light than usual, but the same amount in the visible range. Thus, mathematically combining these two signals can help differentiate plant from non-plant and a healthy plant from a sickly one.
Potential application in retail garden centres
Amazon and convenience store chain 7-Eleven have been trialling drone technology since about 2015. However, Dr Louise Grimmer from the University of Tasmania’s Tasmanian School of Business and Economics believes we are unlikely to see drones in retailing in any meaningful way over the next decade or so, particularly in Australia and New Zealand. Issues around privacy, security, logistics and safety, as well as the limits on weights that drones can accommodate, need to be worked out first.
Drones are unlikely to be used in delivery services any time soon, given the cost and need for operators to remain in the visual line of sight (VLOS) of the drone in operation.