across a broad range of frequencies (from roughly 1000 Hz to greater than 50,000 Hz). ) Extreme rain events produce very loud signals, sometimes as much as 50 d B above the background noise level.Very large raindrops splashing on the ocean surface during an experiment at Kwajalein Atoll in the central Pacific Ocean in 1998. Nystuen, Applied Physics Laboratory, University of Washington.
Specialized rain gauges have been developed for use at sea, but they are easily damaged or stolen when mounted on buoys on the ocean surface.Acoustic Rain Gauges (ARGs) have been developed that can be placed safely beneath the ocean surface to record the sounds produced by rain.The dashed lines show the sound levels due to wind at three different wind speeds.Labeled 3, 5, and 7 meters per second (m/s), approximately 6, 10, and 14 knots, this is the amount of sound that is due to wind alone.The solid lines show the sounds generated by different types of rainfall.
The blue and the green lines are for drizzle, showing a peak in sound from 13 to 25 k Hz.Following the initial impact, sound can radiate from bubbles trapped under water during the splash.For most raindrops, the sound produced by the bubbles is louder.Individual raindrops make sound under water in two ways.The impact of the raindrop hitting the ocean surface makes the first sound.These data are from an ocean surface mooring in the eastern tropical Pacific (Ma et al. The Acoustic Rain Gauge was deployed at 20 m depth. Nystuen, Applied Physics Laboratory, University of Washington.) Rainfall is difficult to measure over the ocean.