Analytic model for matched-filtered scattered intensity of volume inhomogeneities in an ocean waveguide calibrated to measured seabed reverberation

Abstract

In this thesis, we derive full theoretical expressions for the moments of the matched filtered scattered field due to volume inhomogeneities in an ocean waveguide and provide a computationally efficient time harmonic approximation to the matched filtered model. Following the approach developed by Galinde et al 16], the expressions are derived from first principles, by applying Green's theorem and the Born approximation. The scattered field and the total moment expressions are in terms of the fractional changes in the bottom compressibility and density, as well as the waveguide Green function and its gradients. The volume inhomogeneities are assumed to be statistically stationary, and assumed to be correlated in all three directions following a delta correlation function. Sound propagation in the ocean is modeled using the parabolic equation model and actual measurements of bathymetry and sound speed at the experimental locations. Monte Carlo simulations are used to account for the sound speed variability in the ocean waveguide due to internal waves or other sources of acoustic field randomization. The computationally efficient time-harmonic model is shown to provide a good approximation to the full broadband matched filtered model for a standard Pekeris waveguide. The time-harmonic model is then calibrated for ocean bottom reverberation at several frequencies in the 415-1325 Hz band, with data collected during the 2003 and 2006 ONR Geoclutter Experiments on the New Jersey continental shelf and on the northern flank of Georges Bank in the Gulf of Maine, respectively. The statistics for the inverted bottom parameters are summarized for all frequencies and experimental locations considered. The acoustically determined bottom parameters are shown to vary with approximately the wavelength cubed, suggesting that, by different frequencies selecting the scale of the acoustic inhomogeneities, the acoustic effects dominate over the geophysical effects.