ACOUSTIC EFFECTS OF
FRONTS
Figure 9-16.-Mean position of Atlantic fronts.
The following changes can be of significant
importance to acoustics as a front is crossed:
l Near-surface sound speed can change by as much
as 100 ft/sec. Although this is due to the combined effect
of changing temperature and salinity, temperature is
usually the dominant factor.
l Sonic-layer depth (SLD) can change by as much
as 1,000 feet from one side of a front to the other during
certain seasons.
l A change of in-layer and below-layer gradient
usually accompanies a change in surface sound speed
and SLD.
l Depth of the deep sound-channel (DSC) axis can
change by as much as 2,500 feet when crossing from
one water mass to the other.
l Increased biological activity generally found
along a front will increase reverberation and ambient
noise.
l Sea-air interaction along a frontal zone can cause
a dramatic change in sea state and thus increase ambient
levels.
9-17
