The scientific principles behind the altimeter were first written by Rev Alexander Bryce a Scottish minister and astronomer in 1772 who realised that the principles of a barometer could be adjusted to measure height.

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Altitude can be determined based on the measurement of atmospheric pressure. The greater the altitude, the lower the pressure. When a barometeris supplied with a nonlinear calibration so as to indicate altitude, the instrument is called a pressure altimeter or

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After extensive research and experimentation, it has been shown that "phase radio-altimeters" are most suitable for ground effect vehicles, as compared to laser, isotropic or

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In 1931, the US Army Air Corps and General Electric tested a sonic altimeter for aircraft, which was considered more reliable and accurate than one that relied on air pressure when heavy fog or rain was present. The new altimeter used a series of high-pitched sounds

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Global Positioning System (GPS) receivers can also determine altitude by trilateration with four or more satellites. In aircraft, altitude determined using

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The altimeter is an instrument optional in off-road vehicles to aid in navigation. Some high-performance luxury cars that were never intended to leave paved roads, such as the

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A radar altimetermeasures altitude more directly, using the time taken for a radio signal to reflect from the surface back to the aircraft. Alternatively, Frequency Modulated Continuous

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