Across-shelf versus along-shelf coherence length estimates of low-frequency pulse transmissions on the New Jersey continental shelf.

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Sound at 100–400 Hz propagating in approximately 80-m depth water from fixed sources to a joint horizontal/vertical line array (HVLA) is analyzed. The data are from an area east of Delaware Bay in the Mid-Atlantic Bight populated with tidally-generated long- and short-wavelength internal waves that propagate generally shoreward. Two paths are used: a 29-km path in the cross-shore (across internal wave crest) direction and a 19-km path in the along-shore direction. Spatial fluctuations of HLA arrivals have been computed as a function of HLA beam steering angle and time: array gain, horizontally lagged field coherence function, and coherent beam power. These quantities and fitted characteristic coherence scale lengths vary in apparent response to internal-wave variability [Collis et al., J. Acoust. Soc. Am. 124, EL97 (2008)]. In this presentation, coherence length estimates are provided for the month of August 2006. In additional to internal volume effects, consideration is given to signal duration, angle of incidence, and along-shelf versus across-shelf propagation. [Work supported by the Office of Naval Research.]