Characteristics of a new automatic hail recorder

An automatic hail sensor was developed, based on signal production with microphones, a quick signal analysis and recording possibility. For this hail recorder (HARE) small piezo-electric microphones inside a Makrolon body are used to detect hailstones. The prototype has an octagonal shape, two microphones on the top and bottom plates situated in the middle of the device, and an electronic board. A hailstone striking the surface produces waves on the sensor body and a voltage in the piezo-electric microphones. Each hail event is stored in the internal memory including the time and date. The memory can be read out via a USB port at any time after one or more hail events.HARE was tested and calibrated with the help of a newly constructed pneumatic hail gun. The voltage signal at the top plate microphone of HARE increases linearly proportional to hailstone momentum, whereas at the bottom plate it increases linearly proportional to hailstone kinetic energy. For large hailstones the accuracy of HARE is in the order of 10%. Calibration of HARE is still in progress and it has not been tested in real hailfalls as yet.An online device as well as an autonomous one is available for a large number of possible applications. Lately there has been interest to use HARE at solar power plants in Southern Europe to prevent the expensive modules from becoming damaged. Perhaps HARE could also participate in new and existing hail observing networks.