Regression Analysis for Averaged Decay Laws for Energy versus Range in Some Winter and Summer Mediterranean Shallow Water Sound Transmission Data

Abstract

Shallow water broad-band sound transmission data from a SACLANT Centre Mediterranean program have been analyzed, in 20 frequency bands, for evidence for various decay laws for the variation of sound energy with range. The data, averaged over depth, show surprisingly smooth, reproducible variations with range. For example, exponents in power-law regression analysis of winter data (with volume attenuation removed) are close to the often-predicted 32 power with standard deviations often less than 1 dB. There is evidence, at lower frequencies, depending on sea bottom, for a range interval with better propagation (perhaps cylindrical spreading) prior to the 32 power region [see D. E. Weston, J. Sound Vibration 18, 271–287 (1971)] with a more complicated frequency dependence than idealized arguments would suggest. The pertinent aspect of the appearance of various forms of range dependence is the range interval over which they occur; prediction schemes require these limits to arrive at absolute levels. Convincing evidence for various decay laws can be found; however, the range limits may show such complicated dependence on frequency, location, and season that no useful prediction scheme will follow from such a study.