Abstract
A simple model has been derived for down‐slope enhancement (DSE) of underwater sound (the so‐called Megaphone effect). The model predicts DSE for shallow source/deep receiver travel paths across a sloping bottom as the difference between semispherical spreading (15 logR) + αR and cylindrical spreading (10 logR) + αR plus a constant K. In this formulation the frequency dependent attenuation term (αR) is canceled out by the subtraction operation leaving the simple formula: DSE = (5 logR) − K. By comparing measured values of DSE with those computed using this formula, the value of the constant K was found to be about 5 dB when the range R is expressed in nautical miles. DSE for sound crossing the sloping sides of seamounts was found to be about 5 dB higher than that for continental slopes. These models have been used to compute the effective low‐frequency source levels for shipping lanes crossing the continental slopes in areas where the horizontal directionality of ambient noise has been measured. [Work supported by LRAPP.]
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