Principle
- Main article: Radar signal processing
As the name implies, radar (radio detection and ranging) is the underpinning principle of the system. Radio waves are transmitted towards the ground and the time it takes them to be reflected back and return to the aircraft is timed. Because speed, distance and time are all related to each other, the distance from the surface providing the reflection can be calculated as the speed of the radio wave and therefore the time it takes to travel a distance are known quantities.
Alternatively, Frequency Modulated Continuous-wave radar can be used. The greater the frequency shift the further the distance traveled. This method can achieve much better accuracy than the aforementioned for the same outlay and radar altimeters that use frequency modulation are industry standard.
Radar altimeters normally work in the E band, Ka band, or, for more advanced sea-level measurement, S band. Radar altimeters also provide a reliable and accurate method of measuring height above water, when flying long sea-tracks. These are critical for use when operating to and from oil rigs.
Read more about this topic: Radar Altimeter
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