A New Optical Disdrometer for Monitoring Precipitation Microphysics

Abstract:

A new optical-type disdrometer called High-speed Optical Disdrometer (HOD) was developed to observe rainfall microphysical quantities such as raindrop size distribution, shape, fall velocity, and canting. The main components of the HOD are a high-speed video camera, an LED light, and a sensor unit. The camera points to the LED light and captures the silhouettes of the backlit drops that fall in between the camera and the light. When a raindrop is detected, the sensor unit triggers the camera to record sequential raindrop images of up to 1000 frames per second. The captured raindrop images are then digitally processed using a computer software developed to determine the raindrop characteristics. The capabilities of the HOD were evaluated both in the laboratory using high-precision spherical lenses and water drops of known sizes and in the field during rainfall events. These tests showed that the overall performance and measurement accuracy of the HOD were satisfactory. The quality and sequential nature of raindrop images collected during field tests demonstrated the advanced observational capabilities of the HOD, indicating its high potential to become an indispensible instrument for monitoring precipitation microphysics.