OCEANIC RAINFALL DETECTION AND CLASSIFICATION IN TROPICAL AND SUBTROPICAL MESOSCALE CONVECTIVE SYSTEMS USING UNDERWATER ACOUSTIC METHODS

Measurements of the underwater sound produced by rain were made at thr ee U.S. coastal sites in a study to determine the feasibility and limi tations of the acoustic detection and classification of rainfall over water. In the analysis of the rain sound spectra, concurrent radar ref lectivity observations were used to identify convective and stratiform regions of the precipitating clouds overhead. It was found that acous tic classifications of rainfall as to type, based on information in th e 4-30-kHz frequency band, were in general agreement with radar-derive d classifications. The classification technique is based on use of an acoustic discriminant, D-R, defined as the difference in average spect ral levels between the 10-30- and 4-10-kHz bands. A high correlation w as found between sound spectrum levels (in decibels) in the 4-10-kHz f requency band and radar reflectivity, dBZ, suggesting the possible use of the 4-10-kHz band sound spectral level as a classification tool us ing spatially distributed hydrophones in the same way that radar refle ctivity is used in classifying precipitation. The results demonstrate the feasibility of the acoustic method for detecting and classifying r ainfall at sea.