Imaging of pesticide sprays using high speed camera techniques

Macro (spray angle, liquid sheet length, spray distribution) and micro spray characteristics (droplet size and velocity) influence the efficiency of the spray application. Consequently more information on these spray characteristics can lead to a more efficient pesticide usage. This study focuses on measuring spray droplet characteristics using a high speed imaging technique developed by Vulgarakis et al. (2015a).
In the first part, the macro spray characteristics from different types of hydraulic spray nozzles were measured using a developed backlighted image acquisition system and image processing technique. Tests included five different nozzles (Albuz ATR orange and red, TeeJet XR 110 01, XR 110 04 and Al 110 04) (Vulgarakis et al., 2014).
In the second part, micro spray characteristics were determined for the same nozzle pressure combinations. An in-focus droplet criterion was established to decide whether a droplet is in focus and can be measured in an accurate way (Vulgarakis et al., 2016). A calibration system was devised using different sized droplets generated with a piezoelectric droplet generator (Vulgarakis et al., 2015b) at different distances from the focal plane. This enabled measurement of the grey level gradient and the in-focus parameter for every droplet size at various positions. From here, a critical in-focus parameter was established for every droplet size and an in-focus droplet criterion was deduced to decide whether a droplet is in focus or not depending on its diameter and in-focus parameter. The in-focus droplet criterion was applied to spray images and droplet characteristics were calculated. The effects of the nozzle type, nozzle size and measuring position on spray droplet size characteristics were studied.
All imaging results were compared and related well with existing measuring techniques.