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Depth and Range Shift Compensation using Waveguide Invariant Properties

A. Silva,
S.M. Jesus
Institute for Systems and Robotics, University of Algarve
Campus de Gambelas, PT-8005-139 Faro, Portugal
J.P. Gomes,
Institute for Systems and Robotics, IST
Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal

Comments: download file (pdf )
Ref.: Int. Conf. on Underwater Acoustic Measurements, Heraklion, June 2007

Abstract: In most underwater acoustic experiments acoustic sources and hydrophone arrays are moored so as to provide a geometry as controllable as possible. A more operational approach is to use moving sources and light drifting acoustic buoys but in such cases the data exhibits continuous phase and amplitude changes due to depth and range shifts. This may be problematic when the processing of collected acoustic data requires the use of correlation between successive received signals, e.g., in passive time reversal where a probe-signal is sent ahead of the data-signal for post crosscorrelation. An identical problem arises when the source is placed in a continuously moving and unstable autonomous underwater vehicle. Up to now, only the range shift is usually compensated by using data processing techniques, for example, by applying an appropriate frequency shift to the acoustic field based on waveguide invariant theory. This paper formulates the hypothesis that array and source depth fluctuations can also be compensated by using a frequency shift of the received pressure field. Acoustic simulations and real data collected during the MREA’04 experiment suggest that the frequency translation required for the array and source depth compensation can be computed using new invariant properties of the waveguide.

ACKNOWLEDGMENT: This work was supported by Fundação para a Ciência e a Tecnologia under NUACE POSI/CPS/47824/2002 project. The authors would like to thank the NATO Undersea Research Centre for the organization of MREA’04 sea trial, NRV Alliance master and personnel and the scientist in charge Emanuel F. Coelho.