Inversion of head waves in ocean acoustic ambient noise

The virtual head wave is produced through cross-correlation processing of signals containing the real, acoustic head wave. The virtual head wave has the same phase speed as the head wave, but the travel time is offset, thus the term virtual. The virtual head wave, like the real head wave, propagates in a direction corresponding to the seabed critical angle. The virtual head wave travel time varies with array depth and water column depth. However, in a refracting environment, the travel time is also dependent on the depth-dependent sound speed profile. Previously, the virtual head wave was shown as observable from measurements of ocean ambient noise, and the arrival angle was used to estimate the seabed sound speed. By also using the virtual head wave travel times, it is possible to invert for array depth and water column depth. The previous analysis was limited to the assumption of a Pekeris waveguide, which is a special case of the more realistic refracting waveguide. In this paper, the virtual head wave and the inversion method are considered in environments having refracting sound speeds. The theoretical framework and the inversion method are presented along with illustrative simulations and application to the Boundary'03 data.