Seabed Structure Inferences from TREX13 Reflection Measurements

Seabed reflection measurements can be used to infer highly detailed properties of marine sediments. The information content is largely contained in the interference pattern in frequency-angle arising from wave constructive and destructive interference in a plane layer. Wide-angle reflection measurements at a ridge crest and a swale site off the coast of Panama City, FL, USA, instead show interference patterns that are highly perturbed. Interface roughness was hypothesized to be the cause of the perturbations. This hypothesis is examined using numerical simulations. Measured data and simulations at the swale site show broadband peaks and troughs due to focusing/defocusing effects from boundary curvature which perturbs the interference pattern. While the hypothesis roughness is likely correct at the swale site, the roughness statistics are not known sufficiently to validate the hypothesis. At the crest site including roughness did not lead to strong similarities with the data. Interference pattern perturbations at both sites eliminated the possibility of estimating sediment parameters from inversion of broadband wide-angle data. Instead, sediment properties were estimated by inspection and forward modeling. The estimates reasonably agree with geoacoustic properties estimated from normal incidence measurements in the swale and indicate similar sound speeds and densities on two ridges ∼6 km apart.