High‐frequency reciprocal transmissions across a coastal front in Haro Strait, British Columbia

The Haro Strait experiment was conducted in Haro Strait, British Columbia (Canada) in order to determine the feasibility of acoustically focused oceanographic sampling (AFOS). In the course of the experiment 15‐kHz pseudorandom sequences with a bandwidth of 3 kHz were reciprocally transmitted across a front driven by estuarian and tidal forcing. Temperature profiles were continuously measured at the array locations, and array elements were acoustically tracked. Transmissions were performed over a period of 36 h, providing an exhaustive acoustic characterization of the frontal dynamics. The sensitivity of arrival times to the environmental variability is first investigated. Both current and temperature fields across the front are estimated using travel‐time tomography. Resolution issues associated with source–receiver parameters such as geometry, frequency, and bandwidth are discussed in light of the experimental data. Finally, the relevance of the high‐frequency acoustic tomographic inversion to AFOS is assessed. [Work supported by ONR.]