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30 Years of Progress?

30 Years of Progress?. M. G. Brown, F. J. Beron-Vera, I. Rypina, I. Udovydchenkov. Our simple expressions account for the following features of the AET measurements:. the remarkably small (O(ms)) time spreads of the early arrivals;

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30 Years of Progress?

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  1. 30 Years of Progress? M. G. Brown, F. J. Beron-Vera, I. Rypina, I. Udovydchenkov

  2. Our simple expressions account for the following features of the AET measurements: • the remarkably small (O(ms)) time spreads of the early arrivals; • the associated (early arrival) near-lognormal peak intensity pdf; • the large time spreads of the late arrivals; • the associated (late arrival) near-exponential intensity pdf; • the vertical scattering of energy.

  3. Comments on theoretical results • ray and modal phase stability are controlled by the same parameter (a = b) • dependence on the stability parameter a (or b) is multiplicative • derivation of these results does not require that the apex approximation be used • these results suggest that wavefield statistics show very little sensitivity to the structure of dc(z,r) (because of the central limit theorem)

  4. Conclusions • Over the past 30 years progress on understanding underwater acoustic wavefield statistics has been severely hampered by inappropriately assuming that the background c(z) plays a passive role in the process. (Intuition based on the homogeneous background problem fails.) • In the inhomogeneous background problem wavefield statistics at long range are controlled by the background c(z) via a (or b); wavefield statistics show remarkably little sensitivity to the details of dc(z,r). • These statements are supported by ray- and mode-based theoretical results and PE simulations. Agreement between theoretical results and the AET observations is good.

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