Primary radar uses radio waves to detect the distance and speed of objects in the air or on water. Antennas focus the signal in a specific direction. Transponders improve accuracy by sending out a stronger signal with aircraft information. Radar can also track weather and detect possible tornadoes.
A primary radar system sends out a high-power radio frequency from a rotating antenna and uses any reflected signal to determine the distance and speed of objects in the air or on water. The radio signal shows the distance to an object by the time it takes to make the round trip to the object. For radars used in aircraft control, the return signal can also be used to determine the aircraft’s approximate altitude or height above the ground. An antenna is a dish or curved metal structure that focuses a radio beam and transmits it in a specific direction.
Radar is an acronym, or shortened version, of the term “radio detection and range”. First developed for aircraft detection in the 1930s, early radar had limited range due to power limitations for antennas at the time. Although antenna power and software have improved, in the early 21st century the practical limit of primary air traffic radar is about 60 miles (100 kilometers).
Using primary radar requires a lot of signal strength, because objects further away from the antenna will reflect or send a weak signal. At greater distances from the antenna, radar becomes unreliable as a means of determining aircraft position with only reflected signals. The increase in air traffic in the 20th century created the need for other aircraft positioning systems.
Beginning in the 1960s, aircraft began using transponders to assist in air traffic control. A transponder is both a receiver and a transmitter, receiving the radar signal from the main radar and sending out a signal containing aircraft identification, altitude and speed information. This so-called secondary radar improves the accuracy of the aircraft’s position, because the transponder is powered by the aircraft and sends out a stronger signal than a primary radar signal.
Improved transponders since the turn of the 20th century have also provided additional information about the aircraft. Pilots could select settings that would tell an air traffic controller on the ground if the plane is hijacked, or under the control of other people, or if there is an emergency on board. These active signals were sent to the secondary radar receiver located on the same antenna as the primary radar and can be viewed on traffic control screens.
Boats in the water can also be detected with radar systems, with some limitations. High waves can mask or hide the radar returns of smaller boats, and the curvature or shape of the Earth makes it impossible to see boats below the horizon. Large naval vessels may use radar-confusing shapes or coatings that absorb radar to make them appear like much smaller boats on radar screens.
Radar can also be used to track the weather. Water molecules in clouds can reflect certain frequencies of radar signals, which will show clouds containing rain. Early systems could only see moving raindrops, but systems from the late 20th century can detect moisture even without rain.
Doppler radar can detect the speed and direction of water droplets moving through the air. The reflected signal is analyzed by software showing whether the signal is moving towards or away from the antenna. May show rotation that indicates a possible tornado, even at night or when hidden by heavy rain.
Protect your devices with Threat Protection by NordVPN
