CONVERGENCE ZONE REQUIREMENTS
The existence of a convergence zone requires a
negative sound-speed gradient at or near the surface
and a positive gradient below. In addition, there must
be sufficient depth for usable convergence zone to
occur, that is, the water column must be deeper than
the limiting depth by at least 200 fathoms.
SOUND SPEED PROFILE
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.
EXAMPLE OUTPUT
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:
Clear
No CZs
Light
Short range CZs
Medium
Medium range CZs
Heavy
Long range CZs
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:
Clear
No CZs
Medium
Possible CZs
Heavy
Reliable CZs
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.
9-2
