ASA 125th Meeting Ottawa 1993 May

2aUW2. Measurements of low-frequency, low-grazing-angle sea-surface scattering and target strengths.

Roger C. Gauss

Naval Res. Lab., Washington, DC 20375-5350

Joseph M. Fialkowski

Planning Systems Inc., McLean, VA 22102

Direct-path measurements of low-frequency (200--1000 Hz) and low-grazing-angle (<10 deg) acoustic surface scattering were made in the Gulf of Alaska in April of 1990 and in March of 1992. Both narrow-band (cw) and broadband (FM,PRN) transmissions were used to examine the strength of sea-surface backscatter as a function of frequency and environmental conditions. Results have revealed that in addition to a continuously distributed reverberation component, there are often spatially and temporally discrete, high target-strength scattering events. Scattering and target strengths will be presented to quantify the relative contributions of these components to mean backscatter levels (such as were used in deriving the Ogden--Erskine scattering-strength curves), and to extend the scattering-strength results of Ogden and Erskine to lower grazing angles. Furthermore, the presented results have strong implications as to the types of bubble clouds that are responsible for each component (as will be discussed).