Figure 9-7.-A shaded direct path range display.
exist. Half-channel conditions exist where the water
is essentially isothermal from the sea surface to the
bottom, so that sound speed increases continuously
with increasing depth. Under these conditions, the
greatest sound speed is at the bottom of the ocean,
and sound energy will be refracted upward, then
reflected downward at the surface, and refracted
upward again. The effect is similar to a strong
surface duct, so long ranges are possible. Half-
channel propagation is common during winter in the
Mediterranean Sea and polar regions.
There is one graphic output available with
the HAF product. It is a shaded half-channel
conditions display. The half-channel conditions are
indicated by the vertical shading: clear no; heavy yes.
See figure 9-8.
Figure 9-8.-A shaded half-channel conditions display.