An autonomous underwater vehicle technique for in situ waveguide characterization

Results from an autonomous underwater vehicle (AUV) towed hydrophone array experiment are presented as a demonstration of a new in situ measurement technique. In this technique, a source is deployed from a small vessel and the AUV navigates along a pre-programmed path towing the hydrophone array. The added degrees of freedom associated with an array towed by an AUV provides for rapid characterization of the shallow-water waveguide. Using a synthetic aperture, the horizontal wave number spectrum is measured and the modal eigenvalues are experimentally measured by picking off the peak locations in the wave number spectrum. The modal amplitudes are found by using the finite aperture array approximation to the Hankel transform in which the amplitude of the spectral peaks are finite and proportional to the mode excitation amplitude as shown by Frisk et al. [J. Acoust. Soc. Am. 86, 1928–1939 (1989)]. By measuring the modal attenuation, one can determine the effects of bottom interaction. Another measurement technique using the same towed hydrophone system is described in which signal path bottom reflection results are obtained using a parametric source.