Modeling Aerially Applied Sprays: An Update to AGDISP Model Development

AGDISP (AGricultural DISPersal) models the release of aerially applied sprays with a Lagrangian-based droplet tracking algorithm initialized by user inputs (aircraft description, spray boom nozzle locations, drop size distribution, spray material properties, release height, and meteorology). The model offers an extensive set of output plots and toolbox options (deposition, spray block, stream, and multiple application assessments) to predict the downwind behavior of released sprays and assess their potential environmental impact. The model is used in risk analysis, operational planning, post-operation analysis, and training, particularly by the USDA Forest Service (FS) and its cooperators, including the U.S. Environmental Protection Agency (USEPA), the U.S. Fish and Wildlife Service, the U.S. Department of Defense, and various other state and private entities. This article updates the further development of the model since 2003, including the implementation of a quadratic droplet evaporation model and its behavior as Reynolds number approaches zero, a more accurate time step algorithm tied to droplet settling velocity, an optical canopy model, a Gaussian model for far-field extension (downwind to 20 km), an Eulerian model for tracking volatile active spray material, and the Tier 1 ground and orchard assessments previously developed by the Spray Drift Task Force (SDTF). Keywords: Aerial application, AGDISP, Model, Spray drift.