A comparison of spray drift predictions to lidar data

A field trial was conducted to monitor aerially applied pesticide movement above an oak forest in a near-neutral planetary boundary layer using a lidar system. A 36.6-m tower, instrumented at six levels with fast response micrometeorological sensors, recorded wind, turbulence, and temperature profiles during the spray runs. The micrometeorology data was used to drive two spray drift models for a comparison of drift estimates. The models used in this study were USDA Forest Service Cramer-Barry-Grim (FSCBG), an industry standard engineering model, and University of Connecticut Spray Transport (UCST), a heavy particle Lagrangian transport model. Over five spray runs, the FSCBG model predicted < 0.0001% mass fraction deposition occurring beyond 200 m. The UCST model predicted between 0.0034% and 0.3076% deposited beyond 200 m for the same. The lidar returns detected material drift extending out 2000 m from the spray line indicating that both models fall short of predicting the extent of long-range drift drift near-neutral conditions.