Localization using Bartlett matched-field processor sidelobes

Ambiguity surface sidelobes generated by the Bartlett matched-field process or (MFP) shift location with frequency. This sidelobe shift can be viewed a s a continuous trajectory in a range-frequency plane at a fixed depth, wher e the trajectories converge to the correct source range for a perfectly mat ched surface. In isovelocity or bottom-interacting environments the sidelob e trajectories are straight lines that converge to the true range at zero f requency, while environments with upward-refracting sound-speed profiles ha ve trajectories that asymptotically converge as the frequency approaches in finity. This behavior can be explained by the theory of waveguide invariant s, which predict the local behavior of interference maxima/minima of acoust ic intensity in the frequency-range plane. As the ambiguity surface of the Bartlett matched-field processor has a physical interpretation in terms of a time-reversed acoustic field, with the sidelobes analogous to local inter ference maxima, these invariant concepts can be reformulated for applicatio n to MFP. These interference trajectories are demonstrated to exist in simu lations, broadband source tows, and a type A blue whale vocalization. Sidel obe trajectories also exist in the range-depth plane, but they contain no i nformation about the correct source depth. An appendix demonstrates how the se sidelobe properties can be exploited when combining ambiguity surfaces t hrough use of gradient and Radon transform information. The resulting range estimators demonstrate better peak-to-sidelobe ratios than a simple incohe rent average. (C) 2000 Acoustical Society of America. [S0001-4956(oo)01001- 8].