Using photography and image processing for simulated rain drops diameter and velocity measurements

All available methods to measure the properties of natural and simulated rain droplets are costly, cumbersome and time consuming. In this study, high speed photography method and image processing technic used to measure the droplet diameter distribution and velocity of simulated rainfall. ImageJ software and edge detection method used for image processing and droplet size were measured with the accuracy of 1:1000 mm. The results of droplet measurements showed that the simulator can simulate droplets with a diameter range of 2.0 to more than 6 mm at pressure of 20, 40, 60 and 80 Kp. According to the proper operation of rainfall simulator at pressure of 60 Kp, droplets velocity was calculated from 2.1 to 5.7 m/s for different diameter classes at the height of 0.5 m above surface which is close to terminal velocity of natural rainfall. Also Duncan test showed that there are significant differences between the droplet size in four operational pressure and droplet size decreases with increasing operational pressure. The results of this study showed that photography and image processing is a rapid, cost-effective and high accuracy method to characterization of simulated rainfall properties.