Matched field geoacoustic tomography experiments using light bulb sound sources in the Haro Strait sea trial

This paper describes a non-invasive low-frequency acoustic tomography experiment designed to estimate the geoacoustic properties of the ocean bottom over a large area in shallow water. The experiment was carried out in June 1996 during the Haro Strait PRIMER sea trial, a multi-purpose exercise using three vertical line arrays (VLAs) to investigate coastal ocean processes in Haro Strait. The low-frequency tomography experiment was designed to provide acoustic field data for inversion of the bottom properties, and also to acquire ground truth data for comparison with the acoustic estimates. The inversion was carried out using a coherent broadband matched field processing technique. The ground truth measurements included detailed bathymetric and subbottom surveys using differential GPS navigation, and sediment cores and grab samples. The geoacoustic tomography experiments made use of light bulbs deployed at depths from 30-70 m around and within the VLA configuration as sound sources to measure bottom reflectivity, and also to provide data for array element localization. The tomography experiments and procedures for deploying the light bulbs and the coherent broadband inversion method are described, and the estimated geoacoustic profile in the vicinity of one of the VLA sites is presented.