A similar experiment (but to only detect the effect of altitude, not to measure it) was done about 12 years ago, described here: http://www.leapsecond.com/great

A similar experiment (but to only detect the effect of altitude, not to measure it) was done about 12 years ago, described here: http://www.leapsecond.com/great2005/ http://www.leapsecond.com/great2005/