A hydrophone sits beneath the water surface and records the sounds of a summer thunderstorm passing overhead. The hissing of small raindrops hitting the water mingles with the gurgles and plops of larger drops. Occasionally, we hear the bass tones of thunder. These underwater sounds of a rain storm are being carefully recorded by hydrophones (underwater microphones) in remote stretches of ocean and analyzed by scientists to supplement global rainfall measurements.
Different sizes of raindrops produce dramatically different sounds as they hit water, primarily because some sizes of drops generate bubbles and others do not. Because the sound of rain underwater is loud and distinctive, we can use it to detect and measure raindrop sizes and amounts of rainfall over the ocean. Data from remote ocean areas is currently sparse, and this new recording technique will add new data and contribute to a global picture of rainfall. Scientists need these measurements to support climate studies of the distribution and intensity of global rainfall patterns.