Evaluation method of pesticide droplet drift based on laser imaging

Spray drift, which may result in a waste of pesticides and environmental risks, has been viewed as a concern in the use of pesticides. The indoor test of spray drift is mainly measured by the wind tunnel which possess a more stable and controllable wind speed. Recently, the laser is widely used in a range of fields owing to its perfect light stability and the Tyndall phenomenon is remarkable in dispersed particles. Therefore, this paper develops a new method for measuring the drift of pesticide spray in wind tunnels. According to the international standard ISO22856, 11 kinds of additives such as silicone and vegetable oil were measured in the wind tunnel using LU120-01 nozzle from Lechler, Germany. Each additive adjuvant liquid was sprayed for 5 s, repeated 3 times. The collectors were Polytetrafluoroethylene (PTFE) lines and Polyvinyl Chloride (PVC) cards. The PTFE lines were placed at a distance of 2 m from the nozzle in the downwind direction and were 5-85 cm in height (interval 10 cm). The collected droplet particles were analyzed by LS-55 fluorescence analyzer. At the same time, laser imaging technology was used to continuously image during the spraying process. The exposure time is 1/8 s, the ISO is 100 and the aperture is f/1.8. The shutter was controlled by Bluetooth Controller. Combined with computer image rapid batch processing, RGB three-color layer was filtered by MATLAB 2017a, and R-layer minus G-layer image was calculated. The maximum value of gray level and the image feature parameters such as position, barycentric coordinates, and the average value in the horizontal and vertical directions of the image were extracted. The drift rate, feature height and drift potential index (DIX) of the spray drift were calculated from the actual measurement results. The calculated result was fitting with the measured result. The fitting results showed that the maximum value and position of maximum in the x and y axis, the center of gravity coordinates, and the mean value were significantly correlated (Sig. F<0.05) with the drift rate, drift feature height, and DIX. The correlation coefficient was greater than 0.91, the maximum absolute value relative error was only 5.9%. The fitting results of vertical feature height and horizontal feature distance were the best, the average relative error was 0, the absolute relative error was 0.6% and 1.5% (vertical and horizontal direction), followed by DIX index (the absolute relative error of the vertical and horizontal direction were 4.8% and 3.2%) and drift rate (the absolute relative error of the vertical and horizontal direction were 5.9% and 5.3%). It showed that this method could be used to evaluate the drift of droplets accurately. The test speed was faster than the traditional measurement method, and one picture only cost less 1 s for calculation. The test repeatability was high, the DIX index had a comprehensive accuracy of 96%. The test was no needed consumables, which greatly reduced the costing of spray drift testing. The measurement of spray drift in wind tunnels based on laser imaging is an evaluation method that can give one more choice for spraying drift testing.