Air defence is needed for
the protection of naval vessels, moving or stationary army units, air
force bases and all strategic installations and infrastructure. Air
defence units may be based on ground (Surface to Air missile (SAM))
or airborne (air force fighter jets). Both types of units need radars
for target detection and tracking. For ballistic missile defence, the
radar may even be located in space. Radars are also needed for space
surveillance (against spy satellites) like the GRAVES radar of France
but the scope here is limited to aerial surveillance only. For those
who do not know, radar works in air and space whereas sonar is used
underwater (as used by ships and submarines) for surveillance.
Surface to Air missiles are mostly conventional weapons although
nuclear versions (e.g., Nike Hercules) were also made during the Cold
war by super powers.
In order to engage a
target or an airspace intruder (aircraft or ballistic/cruise
missile), it must first be located and this is the job of
surveillance radar. For low-level intrusions, low-level radars are
needed if they are on ground. In general, low-level radars have short
range and medium-to-high-level radars have long range. A good example
of long-range surveillance radar network would be the Canadian NORAD
system for providing early warning of Soviet Union's nuclear bombers
and ballistic missiles. The low-level shortcoming of the ground-based
long-range surveillance radar (due to Earth's Curvature) has been
overcome by airborne radars. Once an intruder is located, it is
passed on to the nearest tracking radar of a SAM system or the
information is relayed to the air force fighters and they pick up the
target on their own airborne radars.
