A simulation study of the variability of acoustic transmissions from Hawaii to Monterey

Abstract

As part of the modeling effort in the Acoustic Thermometry of Ocean Climate (ATOC) project, the influence of mesoscale, gyrescale and seasonal ocean variability on three-dimensional (3D) acoustic ray paths from the planned Hawaii to Monterey site is investigated. Ray paths and signal arrival structure over a two year period are simulated at a six-day interval using a 3D ray-based acoustic model. The input sound speed fields are interpolated from gridded (1/4 degree, 20 level) temperature and salinity output data from the Semtner-Chervin eddy-resolving Parallel Ocean Climate Model. Based on the simulated acoustic multipath arrival structure, the issues of stability and travel time variability are addressed. Bottom topography in the Moonless Mountains region is found to have occasional mild effects on steeper rays. Arrival structure is found to be strongly dependent on depth and quasi-stable over time with a 0.6 correlation between arrival patterns at different times. Travel time variability estimates are 0.42 s rms for steep rays, due to a combination of seasonal and mesoscale ocean variability, and 0.28 s rms for near-axial rays, due primarily to seasonal variability.