Acoustic tomography of a coastal front in Haro Strait, British Columbia

Abstract

An experiment validating the concept of acoustically focused oceanographic sampling (AFOS) was recently implemented in Haro Strait, British Columbia (Canada). Four 16-element vertical receiver arrays were moored around the location of a coastal front driven by estuarine and tidal forcing. Various signals were transmitted from array to array and from a moving source to the arrays over a period of five weeks. Tomographic signals were transmitted over a wide frequency band (150 Hz to 15 kHz). The novelty of the Haro Strait data set resides in its unusual tomographic features: ranges are short (less than 3 km), sound speed perturbations are small (2 to 3 m/s), and currents are relatively strong (3.5 kts). Light-bulb-generated wideband acoustic signals are used in this paper in conjunction with local nonacoustic measurements in order to image the three-dimensional sound speed and current fields within the water mass enclosed by the moored arrays. The combined use of integral and local data leads to a significant decrease of the field estimate uncertainty while maintaining a coverage of the area not achievable by nonacoustic means.