Turning point filters: Analysis of sound propagation on a gyre-scale

Acoustic transmissions from Pioneer Seamount off California to a vertical array near Hawaii are analyzed using a technique which we call a turning-point filter. The observables, travel time and axial inclination, are interpreted in terms of the ocean sound–speed field. The method permits a uniform treatment of the arrival pattern, from the early ray-like arrivals to the late mode-like arrivals, including peak arrivals which cannot be identified as either rays or modes. An adiabatic range dependence is assumed, and Wentzel–Kramers–Brillouin–Jeffreys formalism is applied.