Sediment attenuation effects in sound transmission results from the New Jersey Shelf

Abstract

Experiments were conducted near the site of AMCOR Borehole 6010 on the New Jersey Shelf to characterize propagation predictability. The importance of a non‐linear power‐law frequency dependence of the sediment volume attenuation in the uppermost sediment layer is demonstrated. One metric of transmission loss variation with range is an effective attenuation coefficient that can be extracted from measurements and calculated with the parabolic equation. Previously it was found [W. M. Carey and R. Evans, J. Oceanic Eng., 23] that a power exponent of 1.5 modeled the measurements. The present approach uses 1 kHz as an attenuation reference frequency and employs different parameter ranges and optimization criteria. For 400–1000 Hz, this procedure leads to a power exponent in the range 1.7–2.0, which is consistent with other sand‐silt regions. The estimates are robust with respect to variations in the water and sediment sound‐speed profiles and the sediment layer thickness. The influence of measured range dependence in the sound speed and bathymetry is examined. Estimates of signal time spread are calculated, which can also be obtained for recent experiments in the same ocean region. [Work partially supported by ONR]