The range evolution of the mean wavefront intensity for the long‐range ocean acoustic propagation experiment (LOAPEX) off‐axis source transmissions

Abstract

One of the main objectives of the NPAL 2004 experiment, LOAPEX (Long‐range Ocean Acoustic Propagation EXperiment), which was conducted between 10 September and 10 October 2004, was to better understand the roles of scattering and diffraction in general. The LOAPEX measurement provided acoustic transmission data for ranges of 50, 250, 500, 1000, 1600, 2300, and 3200 km. By placing the source off‐axis in order to avoid exciting low‐order modes, we are able to study phenomena of the significant in‐filling of acoustic energy into the finale region. Our focus will be on the transmissions for the off‐axis source location (nominally 350‐m depth), and the acoustic receptions as recorded on the 1400‐m‐long axial receiving array. The observation of the mean intensity of the wavefront arrival pattern at each range will be compared to deterministic ray and parabolic equation calculations. The following questions will be addressed here: (1) How does high angle acoustic energy from an off‐axis source transfer energy to low angles in the axial region of the waveguide? (2) What are the relative contributions from diffraction and scattering? (3) How does this energy transfer scale with range? [Work supported by ONR.]