Possibilities of using a high-speed camera to characterize falling drops

The accurate characteristics of raindrops play a crucial role in various fields, including meteorology, hydrology, agriculture, horticulture, weather forecasting and atmospheric physics. This can be important, especially in the context of soil splash erosion caused by the impact of raindrops and the consequent transport of soil microorganisms, such as pathogens. At present, the most common technique for measuring precipitation drops is the use of disdrometers, while high-speed imaging technique are becoming more popular. Therefore, the aim of the study was to present the possibilities of using high-speed cameras in order to characterize large falling drops and to compare this methodology with the use of selected disdrometers.

The study was based on the formation of single water drops with specified diameters (3.2, 4.3 and 5.3 mm) and different heights of drop release (1, 3 and 5 m). The analyses included a comparison of data obtained from a single high-speed camera, a set of synchronized high-speed cameras with 3D PTV module (i.e. particle tracking velocimetry) and two types of laser disdrometers (Thies Clima LPM and Parsivel²). Based on the evaluation of the suitability of selected methods for measuring the properties of large drops, it has been shown that high-speed cameras allowed a very accurate analysis of the parameters of individual drops (i.e. size, velocity and shape descriptors) in contrast to the tested disdrometers which showed substantial variability in the results. The calculated coefficient of variation for the measured parameters was up to 5.5% for the cameras, and up to 13.6% for the disdrometers. In this context, high-speed cameras offer an alternative method of measuring processes subject to significant errors, such as those related to the irregularity and variability of the drop shape, in disdrometer-based measurements like throughfall phenomenon. They also serve as a valuable tool for validating widely used instruments.

 

Acknowledgement: this work was financed from the National Science Centre, Poland project no. 2022/45/B/NZ9/00605 and the CTU in Prague project no. SGS23/155/OHK1/3T/11.

Reference: Beczek M., Neumann M., Mazur R., Zumr D., Dostal T., Bieganowski A.: Challenges in measuring the size and velocity of large raindrops: a comparison of selected methods Journal of Hydrology 662, Part B, 133932, 2025