Terrain-following radar
From Wikipedia, the free encyclopedia
Terrain-following radar is an aerospace technology that allows a very-low-flying aircraft to automatically maintain a constant altitude. It is sometimes referred-to as ground hugging, terrain hugging or nap-of-the-earth flight.
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[edit] Usage
This technology is primarily used by military strike aircraft, to enable flight at very low altitudes (sometimes below 100 feet) 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 would have a much larger probability of crashing than an automated system in the same circumstances. It is also sometimes used by civilian aircraft that map the ground and wish to maintain a constant height over it.
Even an automated system has a 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.
[edit] Technology
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.
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 simulatenously.
Aircraft using terrain-following radar can be detected by the emissions from their radars.
[edit] 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.
