ABSTRACT
This chapter addresses the observations that have been made in the field and the physical models that have been developed. Observations have shown that concentrations of this level, or greater, often occur in coastal waters, have been detected several tens of kilometers offshore of the Amazon River, in the Yellow Sea, and in the East China Sea offshore of the Yangtze and Yellow Rivers. The model developed by Diachok will be described since it is considered to be representative of the class of discrete ice-ridge models known to exist, because of its intuitive appeal. The physical model of reflection developed by Twersky was used. The major acoustical processes affecting interaction with the sea floor are: reflection and transmission of energy at the water-sediment interface, refraction of energy by the positive sound-speed gradient in the sediments, and attenuation within the sediments. The velocimeter would seem to be the preferred instrument for obtaining measurements of sound speed in support of naval operations.
