"There was a case couple of decades back where a young man flew a light plane half way across the US without being detected as the air traffic controllers either had their primary radars turned off or thought his echo was from a flock of birds," Brooker says. This used to be called identification friend or foe, or IFF."Īir traffic controllers mostly use secondary radar to track commercial aircraft and only use real radar in the case where transponders are not fitted, are turned off or are broken. "These days, secondary radar is also used, in which a coded pulse sequence is sent to the aircraft and a transponder on the plane generates a coded return, containing a lot of information about the aircraft. "Primary radar is seldom used any more in isolation as there are too many planes in the sky," says Brooker. The air traffic controller - or a computer - can track the echoes or 'blips' on the display to determine where the aircraft is heading. This beam scans around in a circle once every two or three seconds and echoes are displayed on a circular display called a plan-position indicator. This can be accurately determined because the radar signal travels at the speed of light, which is constant.įor air traffic control radars, the beam is shaped like a fan, narrow in the horizontal direction, and wide in the vertical direction, to accommodate high-flying planes. The distance to the target is determined from the time taken between transmitting the pulse and receiving the echo. "Radar makes it possible to determine the direction to an object, generally referred to as the target, based on the direction the antenna is facing," says Brooker. This signal is sent out in short bursts of electromagnetic energy, called pulses, through the antenna which produces a narrow beam like that of a torch. The transmitter consists of an electronic circuit that osciallates at a specific frequency, usually much higher than those frequencies used for radio or TV broadcasts, says Brooker. The word RADAR is an acronym for RAdio Detection And Ranging, and in its simplest form it consists of a transmitted radio signal aimed by an antenna in a particular direction, and a receiver that detects the echoes off any objects in the path of the signal, he says. One of the key means of tracking the position of aircraft is via radar, a system that evolved before World War II and has been constantly refined since then, explains Dr Graham Brooker, a radar engineer at the University of Sydney's School of Aerospace, Mechanical and Mechatronic Engineering. The search for the missing Malaysia Airlines flight 370 this month has raised many questions about how aircraft are tracked.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |