Merchant vessel source level estimation from low-frequency vector sensor systems

Abstract

Low-frequency acoustic vector sensor systems deployed in propagation favorable locations have the potential to not only provide accurate tracking of distant merchant vessels but also, with a combination of AIS data and propagation modeling, produce good estimates of ship source levels. In this work, data from two similar low-frequency acoustic vector sensor systems will be examined using this approach. One system collected data approximately 3 km off the coast of Big Sur, California at the edge of the shelf break, while the other system collected data from a depth of about 900 m near the mouth of the Monterey Bay Canyon. Directional and temporal variations in the ambient noise field will also be evaluated, and causes will be considered including flow noise due to currents, surface (wind) noise, distant shipping, and marine mammals. Bearing estimation results for shipping will be compared with AIS tracks recorded during the periods of deployment. Local sound speed measurements and bathymetry in the vicinity of the deployment area will be used as inputs to a two-dimensional propagation model that properly invokes reciprocity of the acoustic vector field. The results from each system will be compared with the goal of reducing model uncertainty.Low-frequency acoustic vector sensor systems deployed in propagation favorable locations have the potential to not only provide accurate tracking of distant merchant vessels but also, with a combination of AIS data and propagation modeling, produce good estimates of ship source levels. In this work, data from two similar low-frequency acoustic vector sensor systems will be examined using this approach. One system collected data approximately 3 km off the coast of Big Sur, California at the edge of the shelf break, while the other system collected data from a depth of about 900 m near the mouth of the Monterey Bay Canyon. Directional and temporal variations in the ambient noise field will also be evaluated, and causes will be considered including flow noise due to currents, surface (wind) noise, distant shipping, and marine mammals. Bearing estimation results for shipping will be compared with AIS tracks recorded during the periods of deployment. Local sound speed measurements and bathymetry in the vicinit...