Measurements of 3‐D propagation effects at a shelfbreak front

Acoustic data collected on two Webb Slocum gliders deployed by Rutgers University during the Shallow Water Experiment (SW06) on the continental shelf off New Jersey are presented. Acoustic recording systems were attached to the two gliders, which also collected oceanographic data. These gliders periodically surfaced for GPS fixes and data transfer via satellite phone. A major goal of these measurements was to quantify 3‐D propagation effects including the horizontal analog to the classical Lloyd’s mirror. The Lloyd’s mirror effect is produced by the fact that fronts can totally internally reflect sound incident upon them at low grazing angles. The direct and reflected arrivals can add up to produce an interference pattern in range, potentially increasing the received intensity level by 6 dB [Lynch et al., IEEE J. Ocean. Eng., in press]. The gliders crossed the shelfbreak front at ranges of approximately 20 km from the sources and in water depths of approximately 80 m. Measurements of the acoustic arrivals from 224 and 400 Hz tomography sources are compared to 3D modeling results. The increase in the intensity level predicted by the horizontal ray‐vertical mode model is discussed. [Work supported by Office of Naval Research.]