| A first validation of water vapour total column amounts derived from
measurements of the SCanning Imaging Absorption spectroMeter for
Atmospheric CHartographY (SCIAMACHY) in the visible spectral region has been
performed.
For this purpose, SCIAMACHY water vapour data have been determined for the year
2003 using an extended version of the Differential Optical Absorption
Spectroscopy (DOAS) method, called Air Mass Corrected (AMC-DOAS).
The SCIAMACHY results are compared with corresponding water vapour measurements
by the Special Sensor Microwave Imager (SSM/I) and with model data from the
European Centre for Medium-Range Weather Forecasts (ECMWF).
In confirmation of previous results it could be shown that SCIAMACHY derived
water vapour columns are typically slightly lower than both SSM/I and ECMWF
data, especially over ocean areas.
However, these deviations are much smaller than the observed scatter of the
data which is caused by the different temporal and spatial sampling and
resolution of the data sets.
For example, the overall difference with ECMWF data is only
-0.05 g/cm2 whereas the typical scatter is in the order of
0.5 g/cm2.
Both values show almost no variation over the year.
In addition, first monthly means of SCIAMACHY water vapour data have been
computed.
The quality of these monthly means is currently limited by the
availability of calibrated SCIAMACHY spectra.
Nevertheless, first comparisons with ECMWF data show that SCIAMACHY (and
similar instruments) are able to provide a new independent global water vapour
data set. |