Low Frequency Bottom Reflectivity Measurements in the Tufts Abyssal Plain
Ocean bottom reflectivity has been studied at two sites over the Tufts Abyssal Plain in the northeast Pacific Ocean. Measurements of bottom loss were determined from measured propagation loss of the first, second, and third bottom bounce paths over a range of grazing angles from 5° to 75°, and for a number of 1/3 octave bands from 40 Hz to 600 Hz. At these low frequencies the bottom loss versus grazing angle indicates a critical angle behaviour, and the loss extrapolates to a value of 6 dB at normal incidence.
The theoretical bottom loss was computed using a simple two-layer model of the ocean bottom in which the sediment is modeled by a layer with a constant sound speed gradient and constant attenuation, and the underlying mantle crust is modeled by a half space with constant sound speed and attenuation. A good fit with the acoustic measurements was achieved using values of the model parameters obtained from seismic experiments carried out in the study.
KeywordsSound Speed Grazing Angle Ocean Bottom Head Wave Octave Band
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