![]() ![]() These drop size ranges are “minuscule” ( D 2.2 mm), as illustrated in Fig. (1992), in laboratory studies using the full range of drop sizes found in rain, showed that the sound of rain is produced by four acoustically distinct ranges of drop diameters D. 1989 Pumphrey and Crum 1990 Medwin et al. Other studies elaborated on this finding ( Nystuen 1986 Prosperetti et al. In the laboratory, Franz (1959) showed that the main sources of underwater sound in the 0–50-kHz region were the drop impact and the resonance of entrained air bubbles sometimes formed during impact. Nonmilitary interest developed nearly 30 years later when it was realized that sound generated by rain might serve as an estimator of rainfall rates at sea for environmental studies ( Lemon et al. Underwater sound produced by rain has been the subject of much study since World War II, when its impact on the operation of military sonars was first recognized ( Knudsen et al. Literature review-The sound production mechanisms of individual drops Based on rainfall classification analysis of concurrent radar observations, our findings indicate that it appears possible to classify rainfall as to type from measurements of the underwater sound spectrum alone.Ī. In addition, theyshow that the underwater sound of rain is identifiable, with spectral characteristics different from the normally prevailing underwater background noise in the ocean. Many of our results are consistent with the findings of others. Our goal is to determine the feasibility and limitations of using an acoustic method for detecting and classifying rainfall as convective or stratiform. In this paper, typical rainfall events at each site from mesoscale convective systems (MCS) are presented and discussed in detail. The work reported here is the beginning of a detailed analysis of field data collected at three coastal sites along the Atlantic during the period 1988–95. However, to date a thorough investigation in the field has not been attempted. During the past decade, underwater sound measurements of rainfall have shown that rain produces a dominant underwater signal that has the potential of yielding useful estimates of rainfall over water. Although vital to climate modeling and prediction, reliable rainfall estimates for the world’s oceans are largely nonexistent due to the great difficulty of making accurate measurements at sea. The motivation for this work was the critical need for improved observations of rainfall over the ocean. This paper presents new findings on the use of underwater sound for the study and analysis of rainfall at sea. The results demonstrate the feasibility of the acoustic method for detecting and classifying rainfall at sea. A high correlation was found between sound spectrum levels (in decibels) in the 4–10-kHz frequency band and radar reflectivity, dB Z, suggesting the possible use of the 4–10-kHz band sound spectral level as a classification tool using spatially distributed hydrophones in the same way that radar reflectivity is used in classifying precipitation. The classification technique is based on use of an acoustic discriminant, D R, defined as the difference in average spectral levels between the 10–30- and 4–10-kHz bands. It was found that acoustic classifications of rainfall as to type, based on information in the 4–30-kHz frequency band, were in general agreement with radar-derived classifications. In the analysis of the rain sound spectra, concurrent radar reflectivity observations were used to identify convective and stratiform regions of the precipitating clouds overhead. coastal sites in a study to determine the feasibility and limitations of the acoustic detection and classification of rainfall over water. Measurements of the underwater sound produced by rain were made at three U.S. Marine Acoustic Rainfall Measurement System (MARS) and Data Sampling Strategies.2) Effects of wind on the rain sound spectrum and the discriminant.6) Classification of rainfall using an acoustic discriminant.5) Dropsize distribution and rain sound spectrum analysis.3) Radar reflectivity analysis for rainfall classification.Tropical and subtropical mesoscale convective systems and rain-type classification ![]()
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