Acoustic propagation in the coastal environment of the Florida Straits—recent experimental results

Abstract

An autonomous source was moored at ranges of 10 and then 20 km from a vertical receiver array with 32 elements in a depth of 145 m of water. M sequences were transmitted for 28 days at six center frequencies from 100 to 3200 in one octave increments. Arrivals and paths are identified with models and then fluctuation statistics, coherence, and predictability are examined in a parameter space of frequency, range, and receiver depth. A group of refracted-bottom-reflected (RBR) modes/rays has nearly equal group velocities and tends to focus in time and depth forming intense arrivals especially at the depth of the transmitted. A second group of surface reflected bottom reflected (SRBR) modes produce arrivals that fan out in time. Coastal areas inside western boundary currents have exceptionally variable sound speed fields owing to dynamical effects such as meanders, shelf waves, eddies, coastal upwelling and energetic internal waves and tides. Sound speed fluctuations are observed to be an order greater than the deep ocean. Very large changes in mean sound speed profiles and extreme gradients occur at subinertial periods. Also, potential energy of the internal wave field varies with the same longer periods as do statistical properties of observed acoustic signals.