Wars cmd W @y‘àring
205
submarine radio or radar signals. A distinguishing feature of the
Orion is the ‘sting—like’ projection from its tail holding the magnetic
anomaly detector, an instrument which nds submarines by the
disturbance that their hulls create in the Earth’s magnetic eld.
Another device uses a highly sensitive infra—red detector to search
for changes in the temperature of the sea—water caused by coolant
from the nuclear engines. However, heading the list of submarine
sensors used by these aircraft is the air—to—sea search radar developed
from the system which was so successful against U—boats during
the Second World War.
Surface vessels and submarines generally detect underwater
craft accoustically, either by listening with hydrophones for noise,
such as caused by machinery and cavitation, or by actively searching
the surrounding water with sonar—sound—ranging equipment
similar to the sh—detection systems described in Chapter 2.
Helicopters also use sonar devices which they dunk in the sea.
Fast—moving aircraft have to lay their ‘listening posts’ (sonobuoys)
on the surface of the ocean and then circle above, collecting signals
which they relay. A well—laid pattern of sonobuoys gives an Orion
a listening range of about 32,000 square miles, but the reliance of
such highly sophisticated ‘command posts’ upon so tenuous a link
is one of the major weaknesses of submarine detection from the
air.
No matter how sonar systems are deployed, by ship or aircraft,
the influence of water quality on sound and the general noisiness of
the ocean environment curtail their ultimate effectiveness. The
speed of sound in water, about 4,980 feet per second, changes
as temperature and pressure rise, so that sound waves rarely follow
straight paths in the sea. Since the pressure increases and the
temperature generally decreases with depth, the pattern of refrac—
tion, as this bending is known, can be very complex. Changes in
temperature have by far the greatest effect on sounds generated near
the surface. The decrease in temperature away from the sun—
warmed surface bends the sound upwards close to the surface,
and alternate refraction upwards and reection downwards from
the surface ‘traps’ the sound there. Deeper in the ocean where the
temperature becomes more uniform, the increasing pressure
becomes dominant and causes the sound to bend towards the ocean
oor. Between these upward—and downward—curving zones lies a
‘shadow zone’ through which no sound passes and where a submarine
205
submarine radio or radar signals. A distinguishing feature of the
Orion is the ‘sting—like’ projection from its tail holding the magnetic
anomaly detector, an instrument which nds submarines by the
disturbance that their hulls create in the Earth’s magnetic eld.
Another device uses a highly sensitive infra—red detector to search
for changes in the temperature of the sea—water caused by coolant
from the nuclear engines. However, heading the list of submarine
sensors used by these aircraft is the air—to—sea search radar developed
from the system which was so successful against U—boats during
the Second World War.
Surface vessels and submarines generally detect underwater
craft accoustically, either by listening with hydrophones for noise,
such as caused by machinery and cavitation, or by actively searching
the surrounding water with sonar—sound—ranging equipment
similar to the sh—detection systems described in Chapter 2.
Helicopters also use sonar devices which they dunk in the sea.
Fast—moving aircraft have to lay their ‘listening posts’ (sonobuoys)
on the surface of the ocean and then circle above, collecting signals
which they relay. A well—laid pattern of sonobuoys gives an Orion
a listening range of about 32,000 square miles, but the reliance of
such highly sophisticated ‘command posts’ upon so tenuous a link
is one of the major weaknesses of submarine detection from the
air.
No matter how sonar systems are deployed, by ship or aircraft,
the influence of water quality on sound and the general noisiness of
the ocean environment curtail their ultimate effectiveness. The
speed of sound in water, about 4,980 feet per second, changes
as temperature and pressure rise, so that sound waves rarely follow
straight paths in the sea. Since the pressure increases and the
temperature generally decreases with depth, the pattern of refrac—
tion, as this bending is known, can be very complex. Changes in
temperature have by far the greatest effect on sounds generated near
the surface. The decrease in temperature away from the sun—
warmed surface bends the sound upwards close to the surface,
and alternate refraction upwards and reection downwards from
the surface ‘traps’ the sound there. Deeper in the ocean where the
temperature becomes more uniform, the increasing pressure
becomes dominant and causes the sound to bend towards the ocean
oor. Between these upward—and downward—curving zones lies a
‘shadow zone’ through which no sound passes and where a submarine