RADAR
Once a highly classified military secret, radio detection
and ranging
(radar), is now a commonly used electronic device.
Many pleasure boaters use radar to detect other ships at
night or during periods of low visibility. Police use radar to catch speeders.
Speeders use radar detectors to catch police using radar.
The use of radar in civilian aviation has two applications
important to the pilot of an aircraft. Some aircraft have onboard radar sets
that enable the pilot of the aircraft to detect weather conditions that are best
avoided. The radar onboard the aircraft can detect the presence of
precipitation in the form of rain or hail. Heavy rain or hail is an indication
of a thunderstorm that should be avoided by the pilot. Although aircraft can
fly through rain, the presence of heavy rain indicates that moderate or severe
turbulence will be present.
The air traffic control system also uses surveillance radar
to monitor the movement of aircraft within range of the radar antenna. Air
traffic control radar has two modes of operation. Primary radar will identify
an object’s azimuth (direction), and range (distance). Primary radar has
limitations due to rain and hail’s ability to diminish the intensity of radar
signals. Additionally, objects identified by the radar are only classified by
size, i.e. a large aircraft would be a large blip on the radar screen and a
bird would be a very small blip.
In order to make sense of the confusion hundreds of blips
would make on a radar screen, air traffic control uses secondary radar to
identify aircraft. Most civilian aircraft are equipped with transponders. These
transponders are electronic devices that respond to the radar signal received
from a ground station. The ground radar interrogates, or asks, the transponder
aboard the aircraft for a code. The pilot of the aircraft has previously set a
four-number code into the transponder that was assigned to his aircraft by the
air traffic controller. On the controller's radar screen, the aircraft will be
identified with the code that the controller had assigned. Using secondary radar,
the controller has uniform-sized blips with information blocks identifying the
aircraft.
It is a popular misconception that aircraft can locate other
aircraft using on-board radar. Only military aircraft have a capability to
locate another aircraft using radar.
Fly safe,
Captain Robert Perry