The dry atmospheric range correction is designed to correct the observed altimetric sea-surface elevations for propagation delay caused by the dry component of the atmosphere. It requires an estimate of the barometric surface pressure at the satellite nadir point. Given this pressure P in mbar, the dry-atmosphere correction is approximated by [Saastamoinen, 1972]
where q is twice the latitude. This approximation assumes that the dry atmosphere obeys the perfect gas law and that it is in hydrostatic equilibrium. The small second term in parentheses accounts for the variation in surface gravity owing to the Earth's ellipsoidal shape.
The pressure data used here are extracted from the operational model of the European Centre for Medium-Range Weather Forecasting, which is updated every 12 hours (except for TOPEX/POSEIDON where a special 6-hour product has been used).
REFERENCE:
J Saastamoinen, ``Atmospheric correction for the troposphere and
stratosphere in radio ranging of satellites,''
Geophysical Monograph 15, American Geophysical Union, 1972.
EXAMPLE:
This plot shows the mean dry atmosphere correction during the ERS-1
mission's Phase-C Cycle 2, i.e. during the 35-day interval beginning
on 19 May 1992. The mean correction during this period was 2305 mm,
with a standard deviation of 26 mm.
