A Visualization Study on a Relation between the Characteristics of Rain Drop and Rain Sounds
Hisashi Hayashi, Yasushi TSURUTA, Tadaharu ISHIKAWA · Journal of the Visualization Society of Japan · 1996
A preliminary study was made for the development of a new type rain gauge which can estimate the rainfall intensity with a fine time resolution by measuring the intensity of rain sound. A visualization experiment was carried out in order to relate the size of a rain drop to the intensity of rain sound emitted from a tinplate can when the drop hits its roof : Motion of a falling water drop irradiated by stroboscopes from different two angles was recorded by a CCD camera. From the CCD image, in which, the drop appears as a series of a couple of bright points, the drop size and the falling velocity just before it hits the can were estimated. The results showed that the sound intensity was proportional to the kinetic energy of a water drop. Because a natural rain drop falls with the terminal velocity which is determined by its size, the above relation enables us to estimate a volume of a rain drop from the rain sound intensity. The rainfall intensity can be calculated by summing up the volume of rain drops during a unit time.