Impulse response and acoustic fluctuation of high‐frequency signals in a shallow water estuary.

Abstract

Measurements of channel impulse response and its fluctuations in shallow water areas can be used for the prediction of sonar performance, the estimation of active and passive acoustic diver detections, and the prediction of channel characteristics relevant to underwater communication. A shallow water high‐frequency propagation experiment was conducted in the Hudson River near Hoboken, NJ by the Maritime Security Laboratory at Stevens Institute of Technology. Acoustic propagation from an omnidirectional emitter to a receiver was investigated in the frequency band from 20 to 100 kHz for distances up to 100 m in a water depth of 8 m. Frequency sweep signal application was allowed for optimal analysis of the channel impulse response in a wide frequency band. Eigenrays corresponding to direct, surface‐reflected, and bottom‐reflected arrival paths were traced using the BELLHOP program. The fluctuation statistics of narrowband impulse responses for direct, surface‐reflected, and bottom‐reflected arrivals in different frequency bands was estimated. It was found that signals corresponding to the surface‐reflected arrival show considerably higher temporal variation than direct and bottom‐reflected arrivals. Comparison of impulse response for near‐surface and near‐bottom source depths indicates that the bottom‐reflected arrival undergoes significantly high attenuation. [Work supported by ONR Project N00014‐05‐1‐0632: Navy Force Protection Technology Assessment Project.]