Modelling the spray drift by a modified Gaussian tilting plume model.

The increased concern about environmental effect of pesticides use has resulted
in abundant research on spray drift. Spray drift modelling has been developed
to get a better understanding of the parameters involved and better estimation
of the off-target spray deposit. Two groups of models have received extensive
a.ttention: Random-walk and computational fluid dynamics (CFD) models have been used
to predict the effect of: nozzle height, spray pressure, wind speed,... and were
v.alidated with wind tunnels trials. Statistical models based on field trials results have been developed to
estimate off-target spray deposit for different sprayers in various environmental
conditions.
A third group, Gaussian dispersion models, have received early attention in
spray drift modelling but are not so popular, despite their international success
in environmental pollution modelling. The adaptation of such a model to ground
spraying is proposed. The nozzle droplet size distribution measured with a
Malvern laser particle analyser is used to divide the nozzle output into several
size classes. The spray deposit (or footprint) of each diameter class is computed.
The summation of these footprints results in the global drift of the nozzle. The
methodology is applied to derive the drift of a.flat fan nozzle located in a wind
tunnel and the potential of this approach is discussed.