Abstract
Fluctuations in the intensity of sound forward scattered from the sea surface are discussed. The data originate from an experiment off the southern California coastline using the research platform FLIP. Measurements were made using omnidirectional sources suspended from a spar buoy (tethered to FLIP) and receivers mounted on FLIP’s hull, with range varying between 500 and 1000 m. The frequency was 20–50 kHz and the roughness parameter χ=2kh sin θ was ≫1 (where k is acoustic wave number, h rms wave height, and θ grazing angle); thus the measurements represent high-frequency, incoherent scattering in a single surface bounce channel. An often used statistical model for intensity fluctuations in such conditions is the exponential PDF, or its equivalent Rayleigh PDF for amplitude. Examples are presented wherein the exponential model fails a Lilliefors statistical goodness-of-fit test. The Lilliefors test is used for this purpose because parameters of the distribution are not known apriori. An alternative to the single-parameter exponential PDF is the two-parameter gamma PDF. Candidate variables, based on sea state and acquisition geometry that are covariates to the nature of intensity fluctuations, are discussed. [Work supported by ONR Code 321.]
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