### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 1pUW6. A study on intensity fluctuations in forward scattering from the
sea surface.

**Peter H. Dahl
**

**
Donald B. Percival
**

**
**
*Appl. Phys. Lab., College of Ocean and Fishery Sci., Univ. of Washington,
Seattle, WA 98105
*

*
*
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 (chi)=2kh sin (theta)
was >>1 (where k is acoustic wave number, h rms wave height, and (theta)
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 a priori. 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.]