determination of optimal spot roundness variation interval for droplet size analysis on water sensitive paper

to determine the droplet characteristics of agricultural spray nozzles through water sensitive paper (wsp), the non-circular and overlapped spots appearing on the water sensitive paper surfaces are eliminated. in the conventional approach, the procedure is done according to the subjective self determined estimation of the operator. the objective of this study was to develop a practical alternative to the conventional approach to spot elimination (se) from wsp surfaces. droplet samples were taken through application of seven different spray nozzles. papers were placed within and outside the domain of spraying area and scanned at 600 pixels per inch resolution following their collection. the diameter and roundness values of each spot on multiple wsp samples were determined through image processing software. the overlapped spots and the non-circular ones were manually eliminated by the operator. spot roundness (sr) ranged from 0.051 to 6.283 and from 0.130 to 6.283 prior to, and following se, respectively. results indicated a linear relationship between minimum sr value and volume median diameter of the droplets. regression analysis revealed the optimal sr variation interval to be between 0.765 and 2.356 for se. characteristics of the spots remaining out of this range were compatible with the characteristics of the droplets conventional se (when the spots subjectively eliminated). when the volumetric diameters (dv) in the conventional se approach were compared with the optimum sr variation interval (for 10, 50 and 90 percent ratios) their absolute relative error ratios and confidence intervals at 95% level of significance level found as 2.8%±1.4, 1.8%±0.9, and 3.8%±1.5, respectively.