Terrain-following radar

Terrain-following radar

Terrain-following radar (TFR) is an aerospace technology that allows a very-low-flying aircraft to automatically maintain a relatively constant altitude. It is sometimes referred-to as "ground hugging" or "terrain hugging" flight. The term "nape-of-the-earth" flight may also apply but is more commonly used in relation to low-flying military helicopters, which typically do not use terrain-following radar.

Technology and Usage

The system works by transmitting a radar signal towards the ground area in front of the aircraft. The radar returns can then be analysed to see how the terrain ahead varies, which can then be used by the aircraft's autopilot to maintain a reasonably constant height above the earth.

This technology is primarily used by military strike aircraft, to enable flight at very low altitudes (sometimes below 100 feet (30 meters)) and high speeds, avoiding detection by enemy radars and interception by anti-aircraft systems. Under these conditions terrain-following radar is a necessity, since a human pilot cannot react quickly enough to changing terrain heights, and is much more likely to cause a crash than an automated system in the same circumstances.

Some aircraft such as the Tornado IDS have two separate radars, with the smaller one used for terrain-following. However more modern aircraft such as the Rafale with phased array radars can look forwards and at the ground simultaneously.

Most aircraft allow the pilot to select the ride "hardness", to choose between how closely the aircraft tries to keep itself close to the ground and the forces exerted on the pilot. The F-111 uses a switch to select for a hard or a soft ride.

Terrain-following radar is also sometimes used by civilian aircraft that map the ground and wish to maintain a constant height over it.

Military helicopters may also have terrain-following radar. Due to their lower speed and high maneuverability, helicopters are normally able to fly lower than fixed wing aircraft.

Advantages and Disadvantages

By flying at very low altitude, the aircraft can take advantage of terrain masking and avoid detection by enemy radar systems. The system is also largely automated and can take some of the workload off the pilot.

The radar emissions can be detected by enemy anti-aircraft systems with relative ease once there is no covering terrain, allowing the aircraft to be targeted. The use of terrain-following radar is therefore a compromise between the increased survivability due to terrain-masking and the ease with which the aircraft can be targeted if it is seen.

Since the radar cannot tell what is the beyond any immediate terrain, the flight path may suffer from "ballooning" over the top of high ground. Furthermore small obstacles such as radio antennas and electricity pylons may not show up on the radar at all. The objects present collision hazards when flying at very low level.

Even an automated system has limitations and all aircraft with terrain-following radars installed have limits on how low and fast they can fly. Factors such as system response-time, aircraft g-limits and the weather can all limit an aircraft.

Alternatives

There are very few alternatives to using terrain-following radar for high-speed, low altitude flight. TERPROM, a terrain-referenced navigation system provides a limited but passive terrain-following functionality.

List of Aircraft with Terrain-Following Radar

*A7A /B / C /D /E
*F-CK-1 C/D Hsiang Sheng
*B-1B
*B-52H
*F-15E
*F-16
*F-105
*F-111
*Mirage 2000 N
*Mirage 2000 D
*Rafale
*RF-4C Reconnaissance
*Tornado IDS
*Tupolev Tu-160
*Su-22
*A-6 Intruder
*MC-130E/H Combat Talon I/II
* MH-53(M)J Pave Low helicopter

References

* Krachmalnick, F.M., Vetsch, G.J., and Wendl, M.J. (1968) [http://pdf.aiaa.org/jaPreview/JA/1968/PVJAPRE43925.pdf "Automatic flight control system for automatic terrain-following"] , [http://www.aiaa.org/content.cfm?pageid=322&lupubid=22 Journal of Aircraft] 5(2), 168-175.


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • terrain-following radar — vietovės stebėjimo radaras statusas T sritis radioelektronika atitikmenys: angl. terrain following radar vok. Geländebeobachtungsradar, n rus. радиолокационная станция слежения за местностью, f pranc. radar de surveillance de terrain, m …   Radioelektronikos terminų žodynas

  • Terrain Following Radar — radar that track objects on ground level, TFR …   English contemporary dictionary

  • terrain-avoidance radar — A special radar that permits aircraft to be flown safely at a preset clearance level. A normal PPI (plan position indicator) radar enables the terrain to be avoided in azimuth rather than in elevation. A specialist terrain avoidance radar, on the …   Aviation dictionary

  • terrain-clearance radar — A specialist radar system that helps in flying from peak to peak rather than accurately following the terrain contours. Aircraft maintains a pre set height and is warned of obstructions, which are at a pre set slant range away. The instructions… …   Aviation dictionary

  • Radar altimeter — A radar altimeter, radio altimeter, low range radio altimeter (LRRA) or simply RA measures altitude above the terrain presently beneath an aircraft or spacecraft. This type of altimeter provides the distance between the plane and the ground… …   Wikipedia

  • Radar de seguimiento del terreno — El cazabombardero General Dynamics F 111C utiliza tecnología TFR. El radar de seguimiento del terreno, o TFR por sus siglas en inglés (Terrain Following Radar),[1] es una tecnología aeroespacial basada en radar que …   Wikipedia Español

  • radar de surveillance de terrain — vietovės stebėjimo radaras statusas T sritis radioelektronika atitikmenys: angl. terrain following radar vok. Geländebeobachtungsradar, n rus. радиолокационная станция слежения за местностью, f pranc. radar de surveillance de terrain, m …   Radioelektronikos terminų žodynas

  • Radar — For other uses, see Radar (disambiguation). A long range radar antenna, known as ALTAIR, used to detect and track space objects in conjunction with ABM testing at the Ronald Reagan Test Site on Kwajalein Atoll …   Wikipedia

  • radar — /ray dahr/, n. 1. Electronics. a device for determining the presence and location of an object by measuring the time for the echo of a radio wave to return from it and the direction from which it returns. 2. a means or sense of awareness or… …   Universalium

  • Radar signal characteristics — A Radar System uses a Radio Frequency electromagnetic signal reflected from a target to determine information about that target. In any radar system, the signal transmitted and received will exhibit many of the characteristics described below.The …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”