Comparison of FSCBG spray model predictions with field measurements

The FSCBG (Forest Service, Cramer, Barry, and Grim) aerial spray model was developed under joint sponsorship of the U.S. Army and the USDA Forest Service to predict concentration, dosage, and deposition patterns of spray material downwind from aerial releases. A new version of the model incorporates the AGDISP model, which provides a much more rigorous mathematical description of wake effects on drop trajectories than the simple wake effects algorithm of the original FSCBG model. This paper describes graphical and statistical comparisons of deposition measurements from two field programs with model predictions using (a) no wake effects, (b) the simple wake effects of the original model, and (c) the AGDISP (agricultural dispersal) wake effects of the new model. All model versions showed skill in reproducing observed deposition profiles for both data sets. The inclusion of complex wake effects qualitatively improved the correspondence between predictions and measurements in the vicinity of the peak deposition for inwind releases and at the longer downwind distances for crosswind releases. However, statistical performance measures were inconclusive in quantifying this improvement.