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Simple theoretical expressions are generated for the phase and travel-time variations (specifically wander and bias) of normal modes due to scattering by a rough ocean surface. These expressions are explicitly demonstrated for two canonical waveguide examples, the hard-bottom (shallow water) waveguide and the n2-linear (high latitude) waveguide. Numerical examples of the scattering statistics generated for both waveguides are given, and the implications of the examples for shallow-water acoustics, high-latitude acoustics, and ocean acoustic tomography are discussed. An application of the theory developed to the cross coherence of modes measured in an Arctic waveguide during FRAM IV is also shown.
Matched-field inversion of range-dependent geoacoustic properties is studied using broadband (50–200 Hz, 240–260 Hz, and 550–600 Hz) acoustic data collected in the South China Sea during the ASIAEx01 experiment. Range-dependent sediment sound-speed and attenuation profiles are inverted using a global optimization scheme based on genetic algorithms to minimize an objective function defined by the Bartlett processor output. For the forward model, an efficient coupled normal mode model is used to calculate broadband acoustic fields incorporating range-dependent bathymetry and sediment layers thickness obtained by chirp sonar surveys. Inversions were performed starting from a range-independent region with a relatively short source/receiver distance. Additional geoacoustic profiles were inverted by incorporating the previously inverted profiles as the source/receiver distance was increased. The results obtained at three different frequency bands are in good agreement, especially when the range-dependency of bathymetry and sediment layers thickness is included in the inversion. [Work supported by ONR.]
, "A theoretical and simulation study of acoustic normal mode coupling effects due to the Barents Sea Polar Front, with applications to acoustic tomography and matched-field processing," Journal of the Acoustical Society of America, v.100, no. 1 (July 1996) Normal mode coupling due to a shallow water coastal front is considered, using oceanographic data from the 1992 Barents Sea Polar Front ͑BSPF͒ experiment as input to normal mode and parabolic equation ͑PE͒ acoustic propagation models. Criteria for the sensitivity of mode coupling to coastal front widths are derived, and applied to the BSPF as a representative example. The effects of coastal fronts on tomographic schemes are considered, particularly in terms of travel time-based tomography. The effects of frontal mode coupling on matched-field processing schemes are also considered, using both the maximum likelihood and variable coefficient likelihood methods, which show differing sensitivities to mismatch. Finally, directions for future research are discussed.
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