Radar in Modern‐Day Aviation - 180D-FW-2023/Knowledge-Base-Wiki GitHub Wiki
Introduction to Radar
What is radar? Its full form is RAdio Detection And Ranging, which describes its purpose well - to detect objects and their relative positions. This technology was first used by German engineer Christian Hulsmeyer’s ‘Telemobiloscope’ in 1910, whose invention used radio waves to locate ships at sea. [2]
Hulsmeyer's Telemobiloscope worked by emitting pulses of radio waves. These waves, when coming into contact with a metal object, reflected back in a straight line to their source. Its core principle is simple - distance is speed times time. Given that radio waves travel at the constant speed of light, sailors could calculate the distance to a ship by measuring how long it took an emitted wave to reflect back. The direction the device was facing could determine the direction of the detected ships.
This idea gained aviation interest during World War 2. The use of long-range bombers required the US (and their enemies) to identify them in advance, allowing for the use of radar technology. Radar systems played a key role in many military operations in the 1940s, including the detection of warplanes during the Pearl Harbor attack. [3]
However, early radar systems couldn’t differentiate between objects, which led to large, stationary objects like buildings filling up radar screens and confusing people. This issue was resolved with the Doppler shift, making use of the relative motion between the radar and its target. This enhanced radar's capabilities significantly, reducing clutter and enabling widespread use in modern aviation. [1]
Radar in Modern-Day Aviation
Radar is used today for traffic separation by air traffic control, or to put it simply, to prevent aircraft collisions. [4] The Federal Aviation Administration defines minimum standards of separation using both lateral and vertical distances, meaning that aircraft have to either maintain a certain horizontal distance (2000 ft) from other aircraft or maintain a certain height above or below other aircraft (1000 ft). For this to successfully and safely work, radar has to have a high degree of precision, pinpointing the location of aircraft to a few feet. Therefore, regardless of the weather conditions or external factors, radar must function flawlessly to ensure safety in the skies. [5]
These separation systems work using another simple idea - differently shaped antennas. Each antenna is narrow and long, allowing it to dissipate radio wave pulses in a specific plane (refer to image below). Therefore, using two of these antennas allows radar systems to pinpoint the precise location of an aircraft in a 3D space, which allows for adequate separation. 3D radar antennas [6]
The downside of these systems, though, is that they are restricted to a range of under 50 miles, and an azimuth of under 30 degrees [6], which makes this a complicated system to implement across a wide area. The current solution is to use a 3D rotating system of antennas for wide coverage, which the FAA describes as ARSR (Air Route Surveillance Radar). This system allows a much wider area to be covered at the expense of accuracy. This is acceptable from a safety standpoint by requiring aircraft to travel at specific altitudes and speeds when far away from an airport. When near an airport, the more precise systems shown in the image are used.
Radar accuracy is also heavily impacted by the weather. Radio waves normally travel in a straight line, but are bent by temperature inversions, attenuated by clouds and precipitation, and screened / blocked by high terrain features like mountains [6]. The image below shows the dangers of an aircraft being blocked by poor weather. The use of doppler filters, as described above, does significantly help reduce this inaccuracy, but cannot eliminate it.
Lastly, the size of airplanes also matters. With the advent of general aviation, where small piston-driven planes and private jets are significantly smaller in volume and slower than large commercial jets, there is a risk of radar systems not identifying those smaller planes due to misconfiguration, which would be catastrophic.
In addition to the aviation world directly, radar also plays a huge role in weather forecasting, which is crucial for pilots to avoid thunderstorms, minimize turbulence and keep passengers safe. The National Weather Service used polarized radar signals (i.e. signals polarized in two directions) to accurately find the size, shape and variety of different weather phenomena. These computers can identify the amount, intensity, expected timing and type of precipitation, including distinguishing between rain and hail (which is surprisingly a big challenge given the similarity in the two forms). [7]
Solutions and Supplements
Radar technology includes robust backup systems to ensure smooth operation in the event of a system failure. If a primary radar system fails in any way, a backup radar is immediately activated to prevent any lapse in monitoring and control. Moreover, the FAA employs the Air Traffic Control Radar Beacon System (ATCRBS), also known as secondary surveillance radar. It’s a critical part of modern air traffic management, supporting primary radar systems. This system has 3 elements to support radar. Firstly, an Interrogator, located on the ground, works with radar by transmitting specific radio signals that prompt responses from aircraft transponders (a signaling device on all modern aircraft). By directly communicating with these planes instead of relying on reflected radio waves, it ensures planes are clearly represented on a controller’s scope. This significantly enhances the controller’s ability to avoid traffic conflicts.
Secondly, the transponder on the plane also serves a few functions. Each transponder transmits a specific code in reply to a signal from an Interrogator, which is usually stronger than the reflected signals from radar. The controller’s scope also includes a decoder to identify each signal and associate them with an aircraft callsign. Therefore, the ease of identifying and controlling many planes simultaneously rapidly increases. The transponder has served a critical role in preventing many incidents, and its use-case has rapidly grown. Transponders today can squawk special emergency codes that transmit at different frequencies, allowing them to quickly communicate various emergency situations to air traffic controllers with the press of a button. [1]
Eventual Replacement
Radar, while crucial for systems today, has a few disadvantages. In addition to the weather situations listed above, it is also very expensive to operate. [8] The FAA spends over $30M a year operating and sustaining radar systems, which could easily be reduced. The FAA introduced its NEXGEN technologies last decade, and included the transition to Automated Dependent Surveillance Broadcast (ADS-B), which involves aircraft sending their own speeds and positions to air traffic controllers using their transponders, which have proven to be far more accurate and easier to operate than conventional radar. While ADS-B has a lot of requirements, with planes needing to install high-accuracy wide-area GPS systems and new transponders, the FAA is confident that the number of aircraft using the system will continue to grow, to the point where it will be mandatory. [5]
In conclusion, radar technology has been an indispensable tool in aviation,enhancing air traffic control and flight safety. However, its limitations and costs have spurred the development of more advanced systems like ADS-B, which promise greater accuracy and efficiency. As technology evolves, the integration of these new systems will continue to ensure safe and efficient skies in the future.
Sources
https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap4_section_5.html#:~:te xt=Radar%20is%20a%20method%20whereby,return%20to%20the%20receiving%20ant enna. https://www.aviationfile.com/the-evolution-of-radars-in-aviation/ https://www.britannica.com/technology/Distant-Early-Warning-Line https://laartcc.org/stm/radar-separation https://www.faa.gov/air_traffic/publications/atpubs/atc_html/chap5_section_5.html https://skybrary.aero/articles/precision-approach-radar-par https://www.weather.gov/media/lmk/soo/Dual_Pol_Overview.pdf https://www.ifr-magazine.com/training-sims/ads-b-to-replace-radar/