DUCT QUALITY
The quality of transmission in the surface duct
varies greatly with the thickness of the duct, surface
roughness, gradient below the layer, and frequency.
EXAMPLE OUTPUT
There is one graphic output available with the
SFD product. It is a shaded surface duct cutoff
frequency display. The amount of shading indicates
the range of frequencies. See figure 9-6.
Clear
No duct or >300 Hz
Light
150-300 Hz
Medium
50-150 Hz
Heavy
1 -5 0 Hz
DIRECT PATH RANGE (DPR)
LEARNING OBJECTIVES: Understand the
conditions under which DPRs are most likely to
occur. Evaluate the DPR product. Identify the
graphic output of the program.
The DPR displays the most probable ranges that
can be expected for acoustic surveillance system
modes that use direct path propagation. The direct
path is the simplest propagation path. It occurs
where there is approximately a straight-line path
between sonar (source) and target (receiver), with no
reflection and only one change of direction due to
refraction. The maximum range obtained in the
direct path propagation mode occurs out to the point
at which the surface duct limiting ray comes back up
and is reflected from the surface.
EXAMPLE OUTPUT
There is one graphic output available with the
DPR product, a shaded direct path range display. The
amount of shading indicates the range in nmi. See
figure 9-7.
Light
0-2 nmi
Medium
2-4 nmi
Heavy
>4 nmi
HALF-CHANNEL CONDITIONS
(HAF)
LEARNING OBJECTIVES: Understand the
situations that are most favorable for HAF.
Evaluate the HAF product. Identify the graphic
output of the program.
The HAF product displays areas where positive
sound speed profile gradient (half-channel) conditions
Figure 9-6.-A shaded surface duct cutoff frequency display.
9-6
