On the sign of the waveguide invariant

Acoustic propagation in the ocean waveguide is characterized by mutual interference between the multiple ray paths connecting a source-receiver pair. In the Russian literature, these interference effects have been distilled mathematically into a single parameter, the so-called waveguide invariant defined as beta. The conventional wisdom is that the numerical value of beta is negative in deep water and positive in shallow water. In the present work, it is shown how the waveguide invariant can bifurcate and simultaneously have both positive and negative components. When bifurcation occurs, range-frequency mappings of acoustic intensity become fragmented. A method to separate the positive-beta components from the negative is sketched and applied to simulated data. Possible applications are discussed.