Crop Population and Post-Emergence Weed Maps
Crop population and post emergence weed maps require careful consideration of flight parameters, given the requirements of high resolution, low blur, and low GSD. They require specific data collection conditions to generate high quality results. Pay attention to the size of the plants being counted, the flight altitude, the flight speed and the lighting conditions in order to produce a quality population map. Refer to the section Flight Instruction Checklist for more details on planning your data collection missions.
In addition to proper flight planning, data collection for crop population and weed maps must be performed at the right time in the growing season. The Figure below illustrates the size of the plants and spacing between plants required to produce a quality data product. The plants must be large enough to be seen from the air, but not so large that the plants overlap when looking down on them from above. Once gaps between plants close, the accuracy of the population count decreases.
With the proper flight planning, atmospheric, and crop conditions, plant counts with 1-2% error can be achieved. The following conditions must be considered to gather high quality data:
Fly at the recommended altitude based on the plant size, via the flight calculator in the SLANTRANGE DroneDeploy app (typically 40 – 60 m for corn).
The plants must not be overlapping when viewed from above.
There must be sufficient sunlight. If you cannot see your shadow, it is likely too dark for best results with population. The requirement of flying lower and slower combined with dim lighting leads to longer camera exposure times and the potential for image blur.
Controlled ground speed (typically less than 10 m/s, as computed by the SLANTRANGE DroneDeploy app), and minimal pitch/roll excursions. To ensure the minimum 20% overlap is achieved throughout the field: when flying in crosswind, gusting, or otherwise turbulent conditions, set up the mission plan for slightly more overlap (say 25-30%). With a buffer in sidelap, the 20% minimum can be maintained despite aircraft pitch and roll angles that orient the sensor off-nadir.