Measurements of atmospheric attenuation near 225 GHz: Correlation with surface water vapor density

The total attenuation through the earth's atmosphere for radio waves at frequencies near 225 GHz has been monitored for several weeks from a 1-km elevation site. The zenith attenuation at these frequencies was found to be correlated with the ground level water vapor content of the atmosphere; the correlation is consistent with the relation
A
(db)=
0.50 \rho
(
g \dot
m
^-3
of water) predicted for clear sky conditions by theory, assuming a 2-km scale height for water in the atmosphere.