Abstract:

In a multiducted ocean wave guide, energy may be trapped in each of the ducted regions. For sources suitably placed, energy may be stimulated initially in only one of the ducts when eigenfunctions associated with secondary ducts have negligible overlap with the primary duct. For fixed frequency, no energy is transferred, and although high-angle modes eventually traverse to the secondary ducted region, the energy is not trapped there for monochromatic sources. In reality one must take into consideration a spread of frequencies. Monjo and DeFerarri have noted this effect in collecting and interpreting data. This has led to a very exciting phenomenon, the ``Monjo--DeFerarri effect,'' which is quite dramatic for the case they studied. The Monjo--DeFerarri effect is a mechanism whereby energy in a lower duct, with the source in the lower duct, may in time transfer energy to an upper ducted region. The energy transport is cyclical, and at suitably high frequencies energy is trapped in the upper channel in discrete time segments. This leads to the arrival of discrete packets of energy in time which are highly localized spatially. These ``precursors'' arrive in advance of predominant pulse arrivals, and may determine, among other things, the source distance. Here, a study of interductile energy transfer is made for the Yellow Sea. In suitable cases, discrete packets of energy are captured at each high-angle modal contact with the secondary duct. Expressions that predict the arrivals of the upper ducted discrete arrivals, the number in range, the lag time between arrivals, and the lowest frequencies above which this will happen, are presented. [Work sponsored by ONR, NRL, and the University of New Orleans.]