Managing uncertainty in ocean-acoustic tomography

Abstract

The Pacific Missile Range Facility, located off the west coast of Kauai, offers a unique opportunity to perform perpetual tomographic imaging of the sound-speed structure in the region. The range covers over 1100 square miles of ocean and features 172 bottom-mounted hydrophones and 15 bottom-mounted projectors. Data collected during an August, 2001 feasibility experiment suggest that a small subset of the total number of acoustic propagation rays connecting sources and receivers can be used to image prominent oceanographic features such as internal tides. However, acoustic travel time fluctuations occurring over durations of only a few seconds are a potentially significant source of error. Uncertainty in bathymetric relief also prohibits effective utilization of ray paths with multiple surface interactions in the inversion. Results of research intended to better manage these and other uncertainties are presented. The basis of this research is the use of repeated measurements, made every few seconds over many hours, along with a sophisticated ocean circulation model of the region and error decomposition techniques to isolate errors in assumed bathymetry and travel time noise. Inversion improvements as well as approaches to assimilating tomographic measurements into the ocean model are also discussed. [Funding provided by CEROS and ONR.]