Ocean Acoustic Hurricane Detection and Classification

Objectives:The objectives are to use underwater acoustic sensors to classify the intensity or destructive power of hurricanes.Methodology:The approach will be to use a combination of field experiments, laboratory experiments and theoretical analysis to test the objective. The field experiments will involve the construction and deployment of single sensor hydrophones in the path of a hurricane. Measurements of underwater noise level will then be compared wind speed measurements made directly in the hurricane by NOAA Aircraft. They will also involve the use of a new ONR horizontally towed acoustic array to determine the directional spectrum of noise in the vicinity of a hurricane. These measurements will be used to determine if hurricanes can be classified by the same kind of remote sensing techniques previously used to passively monitor submarines over hundreds of kilometers in the deep ocean. The laboratory experiments will involve the use of a wind wave tank previously built by the PIS to measure the dependence of the spectral level and shape of underwater ambient noise on wind speed in a controlled environment. Such measurements do not exist in the field of laboratory for wind speeds above thirty knots but wind speeds typically exceed one hundred knots in hurricanes. It is therefore imperative to determine the empirical relationship between ambient noise level and wind speed in the hurricane regime for underwater acoustic technology to be used in hurricane classification.Rationale:The rationale for this proposal is twofold. The first rationale is based on a possible technological innovation. Underwater acoustic sensors may provide a robust and inexpensive means of classifying the destructive power of hurricanes that may be more robust than other existing methods. The second is based on progress in the pure science of understanding the source mechanisms of underwater noise in the ocean. Very little is known about the source mechanisms for underwater noise at high wind speed. Data relating ambient noise levels and wind speeds in the hurricane regime is essentially non existent. This program would provide the first set of data relating ambient noise to wind speed in the hurricane regime and will lead to a far greater understanding of the source mechanisms of underwater noise due to air-sea interaction in high wind speed.