Which is more accurate for height measurement: GPS or barometer? I am not a pilot and have come to this site to ask a question about the measurement of height.  This is as a result of the comments made as a result of a question in the Physics Stack Exchange forum "Does barometer improve gps accuracy?"  

I feel that there will be more of you on this site who have real time experience with flying and so can answer my question which is:

Which is more accurate for height measurement: GPS or barometer?

I have noted that those engaged in geocaching often have GPS units with built-in barometers to improve height accuracy.

One of my friends who is a pilot responded as follows:


  A light aircraft relies on a barometer that is set to the standard
  1013 millibars when in cruise at height (or the regional QNH when
  lower) but they set to the local reading for the airfield (QFE) when
  planning their decent. Commercial aircraft also have ground proximity
  radar but they also have a standard set of old fashioned flight
  instruments in case the electronics fail. My old aircraft GPS did
  indeed read out height as well but you were told never to rely on it!
For surveying glacier movement, or a mountain range's growth/decay, GPS is more accurate.

For airplanes: refresh rate, reliability, and simplicity matter more. When it comes down to accuracy, ground augmented GPS provides ILS CAT I accuracy using LPV. So alongside refresh rate, and accuracy, comes the question of application. For airplanes in cruise, where separation matters, reliable devices are best.

GPS signals can be jammed. As can be seen in the news lately in California and Egypt. And GPS signal can be lost due to ionospheric interference. So, any equipment that doesn't rely on external sources is safer.