DEPTH AND RANGE SHIFT COMPENSATION USING WAVEGUIDE INVARIANT PROPERTIES

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.