The existence and characteristics of deep convergence or focusing zones have been investigated by means of ray diagrams and field measurements using explosive charges dropped from an aricraft. The zones are found to migrate regularly with change of receiver depth, and exhibit at convergence gain of 5–10 dB for a source depth of 800 ft for the velocity profile applying for the field measurements. The pattern of the caustics that bound these zones in the deep ocean channel is a complex one, but can be roughly characterized as a series of double caustics branching out from the ray that is horizontal at the depth of the source in the ray diagrams.

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