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Technology behind distance measurement in air from ground level.


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What is the technology behind distance measurement in Kilometres or Miles while traveling in plane which is above the sky?

Is it Satellite providing real time distance measurement information to the aircrew members and passengers?


Is it altimeter instrument fixed in the aircraft cockpit?


Is it Radar technology ?


something else ....


Thanks & Regards,

Prashant S Akerkar

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Atmospheric pressure was and is still used in aircraft.  The pilot would set the instrument before take off.   Somewhat accurate.  Air craft Radar altimeters work bouncing high frequency radio waves off the ground.  GPS works by measuring the time radio waves take to get from the various satellites to your GPS gadget.  Lasers are used for precise measurements.  Lasers are higher frequency than radio waves.  More accurate?  Dunno.  Sometimes all work together.

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2 hours ago, prashantakerkar said:

Maybe Radar Altimeter is the instrument which gives us the precise distance measurement in air.

Only in good atmospheric conditions.


There was airplane disaster. Hail damaged radar altimeter and it started showing ground level which confused autopilot and pilots (in cabin there was alarm "terrain ahead, pull up" when airplane was still at ~5 km), hail also damaged the all engines, and caused crash of airplane.


GPS, radio altimeter, laser, the all can stop working when there is some obstacle between them, and the ground, or satellite. Or if they were damaged.

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