The GDS model – a Rapid Computational Technique for the Calculation of Aircraft Spray Drift Buffer Distances

A model for predicting the required spray drift buffer distance for a specified off target deposition level is described. The GDS model is based upon Gaussian diffusion and sedimentation of particles originating from an elevated instantaneous line source. Aircraftinduced near wake effects are ignored. Agreement between aircraft wake models FSCBG, AgDRIFT and the GDS model is reasonable for downwind distances greater than 50m. The model has the advantage over Lagrangian models in that it is faster computationally and can readily provide real time prediction in the cockpit over large distances (3 km). A sensitivity analysis has been performed on the model to elucidate the effects of the primary parameters on spray drift. The model has proved useful in the determination of spray drift buffer distances for regulatory purposes and in the development of appropriate spray drift management systems for aerial spraying. Further research work is required to refine the model to better account for air stability effects, collector type, evaporation and crop canopy.