Abstract:

The possibility of ocean acoustic tomography in its usual form is based on ray perturbation theory and the following assumption: Eigenrays computed in an unperturbed ocean model agree one-to-one with eigenrays computed in the actual perturbed ocean. Using a ray numerical model with an environment containing idealized mesoscale structure, the perturbation strength (cursive beta) is gradually increased and it is found that the multiplicity of eigenrays increases exponentially due to ray chaos. When the multiplicity changes then ray perturbation theory, even to very high order, necessarily breaks down. Bifurcation diagrams show eigenray travel times versus (cursive beta), and at critical values of (cursive beta) pairs of new eigenrays suddenly appear as triplications in accordance with catastrophe theory. Such plots dramatically display the breakdown of ray perturbation theory. The methodology that has been developed should be useful for understanding the limitations of ocean acoustic tomography. [Work supported by ONR.]