The sound speed profile of the deep ocean varies with latitude. In cold surface waters the depth of the deep sound channel axis is shallow, the range to the convergence zone is small, and the range interval between zones is small. In the Mediterranean Sea, the bottom water is much warmer than in the open ocean and, consequently, the sound speed near the bottom is higher. Since the limiting depth is much shallower and the acoustic energy is refracted upward at a much shallower depth, ranges are much shorter than those generally found in the open ocean. Although the acoustic characteristics and sufficient depth excess for convergence zone propagation may exist, bathymetry does play a role as the presence of a seamount or ridge may block the convergence zone path.

There are two graphic outputs available with the CZR product.

1. A shaded convergence zone range display, which depicts areas of predicted range in nautical miles (nmi). See figure 9-1. The amount of the shading indicates the range as follows:

2. The shaded convergence zone usage product displays the areas of CZ probability based on an analysis of depth and/or sound speed excess. See figure 9-2. The amount of shading indicates the probability as follows:

BOTTOM BOUNCE RANGE (BBR)

LEARNING OBJECTIVES: Explain the theory associated with the BBR. Evaluate BBR products. Identify the two graphic outputs of the product.

The BBR product provides an estimate of the horizontal ranges expected for active sonars operating in the bottom bounce mode.

Figure 9-1.-A shaded convergence zone range display.

Figure 9-2.-A shaded contoured convergence zone probability display.

In the bottom bounce mode, sound energy is directed towards the bottom. This path is successful because the angle of the sound ray path is such that the sound energy is affected to a lesser degree by sound speed changes than the more nearly horizontal ray paths of other transmission modes (that is, surface duct, deep sound channel, convergence zone).

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