Jeffrey A. Nystuen
Dept. of Phys., Naval Postgraduate School, Monterey, CA 93943
Previously, this group has demonstrated that the underwater sound due to 1-mm-diam (``small'') water drops is a function of surface slope [Medwin et al., J. Acoust. Soc. Am. 88, 413 (1990)]. It has also been shown that ``large'' raindrops of diameter >2.2 mm cause a splash that creates strong microbubble radiation of frequency 2--10 kHz [H. Medwin et al., J. Acoust. Soc. Am. 92, 1613--1623 (1992)]. The most recent experiments with terminal speed large drops reveal that the microbubble phenomena are affected by the local angle of incidence of the large water drop and that, in addition to the splash microjet creation of bubbles, the small aerosols from the splash also generate microbubbles. The new observations add distinctive characteristics to the spectrum of rain noise that will be useful in solving the inverse problem of determining rainfall from underwater sound. [Work supported by the Office of Naval Research.] [sup a)]Lt., US Navy. [sup b)]Oceanogr. Dept.