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).
RANGE VERSUS DEPTH
Long-range paths can occur with water depths
greater than 1,000 fathoms, depending on bottom
slope. At shallower depths high intensity loss is
produced from multiple-reflected bottom bounce
paths that develop between the source and receiver.
Since 85 percent of the ocean is deeper than 1,000
fathoms and bottom slopes are generally less than or
equal to 1°, relatively steep angles can be used for
single bottom reflection. With steeply inclined rays,
transmission is relatively free from thermal effects at
the surface, and the major part of the sound path is
in nearly stable water.
ACTIVE DETECTION
Inactive detection, bottom bounce transmission
can produce extended ranges with fewer shadow
zones because more than one single-reflected bottom
path exists between the sonar and the target. These
paths combine to produce an increase in the received
signal and reduce the extent of the shadow zone. The
major factors affecting bottom bounce transmission
include the angle at which the sound ray strikes the
bottom (grazing angle), the sound frequency, the
bottom composition, and the bottom roughness.
EXAMPLE OUTPUT
There are two graphic outputs available with the
BBR product.
1. A shaded bottom bounce range display. The
amount of shading indicates the range in nmi. See
figure 9-3.
Light
1-5 nmi range
Medium
5-10 nmi range
Heavy
>10 nmi range
2. A shaded bottom bounce probability display. This
product provides estimates of the existence of low-loss
bottom bounce paths between a sonar (source) and
the target (receiver) based on the environmental and
geoacoustic parameters. See figure 9-4. The amount
of shading indicates the probability conditions as
follows:
Clear
No
Medium
Fair
Heavy
Good
9-3
