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A Physical Explanation For Less Than Quadratic Recorded Attenuation Values

A review of experimental evidence shows that the low frequency attenuation of compressional acoustic waves in sandy marine sediments obeys a simple power law consistent with a frequency dependent attenuation proportional to fn , n =1.0. This observation is in general agreement with Biot's model (1956) for frequencies less than 1 kHz. Recent theoretical work [A. D. Pierce etal., Proc. Oceans 2005, Brest, FR. (2005)] shows that in this lower frequency range, a quadratic dependence (n=2) is to be expected and is decreased by predictable modal propagation characteristics in shallow water. Physical properties and depth-dependent characteristics of the sediment are used to explain the apparent n=18 power law dependence of attenuation. Calculations performed using parabolic equation codes with simplified Biot geoacoustic profiles are compared to experimental results.