Validation of the spray drift modeling software AGDISPpro applied to remotely piloted aerial application systems

Regulatory bodies worldwide are currently developing modeling frameworks to simulate pesticide drift following applications from remotely piloted aerial application systems (RPAAS). Unfortunately, there are no currently validated mechanistic models that simulate off-target droplet movement from these systems. To respond to this modeling gap, we evaluated AGDISPpro, an established Lagrangian-based drift and deposition model following applications by fixed and rotary wing aircraft. Specifically, we evaluated two of the nine RPAAS models available in AGDISPpro, i.e., PV22 quadcopter and PV35X hexacopter models. Our detailed evaluation relied on two sets of field studies: a series of single-swath applications using medium and extremely coarse spray nozzles, and a series of four-swath applications using fine and ultra coarse spray nozzles. AGDISPpro model predictions were compared to in-swath and downwind deposition measurements. The r index of agreement ranged from 0.47 to 0.92 for medium nozzles, 0.61-0.94 for extremely coarse nozzles, and from 0.86 to 0.93 to 0.48-0.55 for fine and ultra-coarse nozzles respectively. There is uncertainty regarding how swath width and swath displacement behavior from the RPAAS affect the location, width, and magnitude of the peak deposition and deposition plume. Thus, further research is required to reduce this uncertainty. Overall, this study demonstrates that AGDISPpro is a promising tool for modeling off-target spray deposition effects from RPAAS.