Another alternative is to assume that you know the water vapor content,
either from a previous measurement and assuming the weather is stable, or
from theoretical curves as a function of pressure, temperature and relative
humidity. With the knowledge of the atmospheric parameters, the model
predicts and
. In this mode, instead of
above, you
must supply
the amount of precipitable water vapor in millimeter.
is then given by (from Eq. 7)
![]() |
(11) |
This is what happens in OBS when used in AUTO mode (specified by OBSSET CAL AUTO) and when you do a CAL command without the
argument COLD.