Radio altimeter

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USSR FLARak radar altimeter PRW-17

Radio altimeter or radar altimeter is a specialized, mostly ground-based radar device for two-dimensional coordinate measurement of elevation angle and distance and the derived height of the located objects. Often they are also given the common name "Höhenfinder", which is an incorrect translation of the English term Height-Finder . Radio altimeters were used to record the altitude of flight targets in radar guidance, weapons control and FLARak systems.

Principle of a range height indicator (RHI scope) of a radio altimeter

To defend against enemy aircraft, in addition to their geographical position, it is important to know the exact flight altitude. Usually two radar devices worked as a pair: a circular search radar (with panorama screen ) coupled with a radio altimeter (with RHI-Scope ), the display devices of which were mostly set up one above the other. The antenna of a radio altimeter is mechanically swiveled up and down at a set angle every 1 to 2 seconds. The antenna diagram is a horizontal fan diagram with a horizontal beam width of about 3 to 5 ° and a very narrow vertical beam width of less than one degree. The all-round radar enabled a map-like overview of all aspects of the radar display, the radio altimeter was aimed at a specific target at a lateral angle and was able to measure its elevation angle and the exact flight altitude. The disadvantage was that the radio altimeter had to be adjusted to a given angle using a hand crank. The measurement of all three coordinates (lateral angle, distance, height) of a target was very time-consuming. Several PRW-13 or PRW-17 radio altimeters could also be coupled to radar devices with a very long range, such as the Kabina 66 .

The radio altimeter lost its importance with the modern devices that mainly operated as multifunctional 3D radar. This development can be clearly seen on the NATO radar display on the Großer Arber : In the front radome there used to be an AN / FPS-6 radio altimeter , and the rear radar. After the installation of the RRP 117 3D radar , the radio altimeter became superfluous, and the radome has been used for purposes other than intended.