Observations of mode scattering from axial and off-axial sources in the North Eastern Pacific, Long Range Ocean Acoustic Propagation Experiment.

Abstract

Experimental observations of the axial modes across range are crucial to verify and complement existing theories for internal-wave induced mode scattering. The 2004 Long Range Ocean Acoustic Propagation Experiment (LOAPEX) was conducted with the main objective of analyzing internal-wave induced mode fluctuations at ranges of 50–3200 km. During LOAPEX, a 75 Hz broadband source made transmissions at an off-axial depth of 350 m and an axial-depth of 800 m. The transmissions were received across a 40 element vertical array capable of resolving the first ten acoustic modes. The mode arrivals from the two source depths significantly differ from each other. For the axial source, the observed mode arrivals are strongly influenced by the low modes directly excited at the source or by nearest neighbor coupling. The shallow source in contrast excites the low modes at a much lower energy, and thus the axial arrivals from the shallow source transmissions are due to scattering from the high modes. This talk discusses the LOAPEX mode statistics for the two source depths. The observed mode statistics are compared with predictions from theory and simulations. [Work sponsored by a National Research Council Research Associateship Award at Naval Postgraduate School.]