Calculation of swath width and swath displacement for uncrewed aerial spray systems

Authors: BONDS, JANE - Bonds Consulting Group; Fritz, Bradley - Brad; THISTLE, HAROLD - Forest Service (FS)

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2023
Publication Date: 3/12/2023
Citation: Bonds, J., Fritz, B.K., Thistle, H. 2023. Calculation of swath width and swath displacement for uncrewed aerial spray systems. Applied Engineering in Agriculture. 66(3):523-532. https://doi.org/10.13031/ja.15400.
DOI: https://doi.org/10.13031/ja.15400

Interpretive Summary: The use of UAVs for spray applications of crop protection products is increasing, though limited data and guidance is available on their proper setup and use in order to ensure efficacy while minimizing off-target movement. A UAV sprayer was evaluated for spray deposition and drift characteristics under a range of operational conditions and a method was developed to determine the offset of the spray deposits from the line of application and the flight-line spacing required to achieve a targeted dosage rate. Results showed highly variable deposits that were significantly offset from the site of application, particularly when smaller droplet sizes are applied at higher wind speeds. Flight-line spacing required to deliver targeted dose rates varied by applied droplet size and wind conditions, with finer spray application resulting in significantly greater downwind deposits than larger sprays. However, the determined spray deposit offset distances correlated well with wind speeds for given spray droplet size applications. The developed methods provide UAV spray applicators guidance on the determination of proper flight-line spacing to achieve required dose rates and use of appropriate flight-line offsets for precision application with minimal off-target movement.

Technical Abstract: Recent research has focused on the use of Uncrewed Aerial Spray Systems (UASS) for their potential to fill the gap between crewed aircraft and ground application, with UASS being able to be used over less accessible areas than ground equipment, being more appropriate to treat smaller, dispersed targets and typically available at reduced cost and complexity when compared to crewed aircraft. However, there is limited literature focused on the proper setup and use of these systems. The objective of this study was to design and conduct a series of large scale, conceptually linked studies to provide data that is used to guide system optimization and development of predictive models. An uncrewed system coupled with three nozzle types covering three droplet size classifications were used to conduct a swath characterization and drift trials designed to establish effective swath widths, deposition variability, swath displacement, and drift. System and nozzle type, along with nozzle position and wind direction significantly impacted the spray deposition patterns within and downwind of the effective swath. The spray distribution in swath is highly variable to the point that using the typical metric of uniformity alone to define swath can no longer apply. In addition, the swath was rarely found to be directly beneath the flightline, and swath offsetting can be significant and larger than the assumed swath width. An iterative solution has been developed that uses a combination of effective dose and uniformity to define swath width. The offsetting of the swath due to interactions with ambient air has also been defined using Center of Deposition. The aim is to be able to distinguish between in-swath deposition and drift. The approach to defining swath width and the displacement of the swath is presented. The goal is to develop a real time onboard navigation system that can reset the flight line in response to wind driven swath displacement. This allows increased deposition within the target zone and reduces off target losses.