LONG-TERM GOALS

One research goal developed from conducted shallow water (SW) acoustic transmission experiments in sandy-silty areas [1] revealed a nonlinear power law frequency-dependent attenuation at lower frequencies ( ≤ 1 kHz) consistent with results reviewed in [2-4] and the observations by the ONR-HEP program. The Biot Theory [5] predicts that the sandy- sediment frequency-dependent attenuation should be quadratic, withnoo)f/f)(f()f ( αα = 2=n; however the observed dependence was. Thus the long-range goal was to develop a simplified theory of sediment attenuation [6] verified by measurements that could explain this dependence and be applied to ocean sediments. 0.21.8 n ±= The second research goal is the development of a quantitative understanding and a theoretical treatment of the scattering of sound by non spherical compressible objects such as bubbles. OBJECTIVE The objective of the work, discussed in this annual report, was to determine the frequency dependent attenuation and phase speed characteristics of selected sandy and muddy sediments (both water saturated and partially saturated) at the lower frequencies to verify a simplified Biot theory] and to provide a theoretical / experimental basis for the water-sediment boundary condition necessary for the accurate prediction of wide band transmission loss in shallow waters