Impact of thermocline variability on underwater acoustic communications: Results from KauaiEx

In July 2003, the KauaiEx, high-frequency acoustic experiments were conducted off the coast of Kauai, Hawaii. Both acoustic communications signals and probe signals (to measure the channel impulse response) were transmitted in the 8-50 kHz band. These signals were transmitted over several days from fixed and moving platforms and were received at multiple ranges and depths using vertical arrays and single hydrophones. Extensive environmental measurements were made simultaneous to the acoustic transmissions (e.g. measurements of the water column temperature structure, wind speed and surface wave heights). The experimental site has a relatively reflective seabed made up of sand that was combined with highly variable oceanographic conditions which led to communications performance closely tied to source/receiver geometry. In this paper, the correlation between environmental factors and communications performance will be discussed. The focus is on communications signals in the 8-13 and 14-19 kHz frequency bands at source receiver range of 3 km. Results show the performance in the higher band was approximately the same as for the lower band. Results also show a strong dependence on receiver depth with the deeper hydrophones having fewer bit errors. The ocean sound speed structure at this site appears to have a large impact on the communications performance and the time variability.