Spray drop measurements using depth from defocus

Sprays are typically characterised by providing local drop size and velocity distributions and number density. The present work examines the possibility of obtaining such information using backlight photography, whereby two cameras are employed and the size and position of each imaged drop is obtained using a depth from defocus approach. A simple algorithm for estimating size and position from the two camera images is introduced and the sensitivity of this algorithm to various system parameters is investigated with simulations using synthetic images, measurements from a calibration facility, and measurements conducted in a sparse spray. Comparison measurements using the analysis of focused images are provided.