Shallow - Water Tracking in the Sea of Nazaré

In the summer of 1996, an experiment was conducted off the coast of Portugal to study the effects of internal tides on sound propagation. This experiment—called INTIMATE '96 (Internal Tide Investigation by Means of Acoustic Tomography Experiment)—has provided a great deal of insight about the variability of pulse transmission over space and time. In contrast to a common view of shallow-water propagation as complicated and unpredictable, we find a steady pattern of echoes. The echo-pattern stretches and shrinks in a systematic way with the tides and allows us to infer the components of the first few oceanographic modes. We also used the echopattern to track the source over a period of several days. During this period the isotherms in the ocean wavered by 20 m as a result of the tides, providing a challenge for model-based tracking. We will discuss these acoustic results with emphasis on the source tracking. Keywords— tomography, tides, matched-field processing 1 On sabbatical from the Center for Communications and Signal Processing Research and Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, NJ 07102. M.B. Porter*, Y. Stéphan**, X. Démoulin**, S. Jesus, E. Coelho, *Marine Physical Laboratory, Scripps Institution of Oceanography, La Jolla, CA, USA. E-mail: [email protected] **EPSHOM/CMO, BP426, F-29275, Brest, FRANCE University of the Algarve, Faro, PORTUGAL Hydrographic Institute, P-1296, Lisbon, PORTUGAL SHALLOW-WATER TRACKING IN THE SEA OF NAZARÉ Submitted to the IEEE Journal of Oceanic Engineering (1998)