Comparing the effects of internal waves, mode coupling, and change in bandwidth of a radiated signal on low mode energy propagation.

Abstract

Wideband signal propagation modeling is carried out for the actual space‐time configuration realized during the long‐range ocean acoustic propagation experiment (LOAPEX) conducted in the North Pacific in 2004. In particular, the experiment used the Kauai transmit station that was located at a range of 2432 km from a vertical line array (VLA), M‐sequence at 75 Hz, and a source depth of 800 m close to the depth of a sound‐channel axis. Two sound speed profiles were utilized to get the smooth two‐dimensional sound speed field. The first one was the profile obtained from the conductivity‐temperature‐depth (CTD) measurements at the Kauai station. The second sound speed profile from the VLA location was based on a CTD cast taken at station T50 (50 km from the VLA). To take into account the acoustic fluctuations due to internal waves, the buoyancy frequency profile based on LOAPEX CTD measurements made at station T50 was used. For simulations, 512 values of the horizontal wave number were utilized with the maximal mode number equal to 50. The low modes intensity received by the hydrophones close to the sound channel axis at the VLA is compared with the results of simulations. [Work supported by ONR and ONR Global.]