Intensity fluctuations. Part II: Comparison with the Cobb experiment

The intensity fluctuations measured at 4 and 8 kHz in the Cobb experiment have been available for nearly 10 years and in that time have not successfully been predicted theoretically. We show that multiple scatter effects must be considered, and that neither the Born nor the Rytov approximation to the scattering formulation is appropriate. A companion paper [J. Acoust. Soc. Am. 74, 1474–14832  (1983)] provides the theoretical background for this work by presenting a general form of the analytical solution to the fourth moment equation in two dimensions for a point source transmission. We use the parameters of the Garrett–Munk model of the internal wave field appropriate to the Cobb experiment oceanographic regime to obtain the correlation functions of the acoustic refractive index field, and then predict the intensity fluctuations. We discuss corrections to the predicted spectrum that are due to fine structure effects and tidal motions. We include a discussion of the scattering parameters Γ and X, which are the scattering and range scaling parameters of the moment equation formulation, and the parameters of the path integral formulation, Γ and Φ. We present a discussion of the measured correlation functions taken during a more recent experiment at Cobb seamount and indicate the directions we need to take to bring the scattering predictions based on internal waves and finestructure into closer agreement with experiment.