Total column water vapour from SSM/I and MERIS at 0.5°

The combined SSM/I+MERIS total column water vapour (TCWV) data record was derived on a global grid
over ocean and cloud free land, with a spatial resolution of 0.5° over ice-free ocean (SSM/I) and
0.05° over land and coastal ocean (MERIS) and stored in NetCDF files that are fully compliant with
the NetCDF Climate Forecast convention. Ocean area with sun glint, where SSM/I observations are not
available, is blended with gridded MERIS data. In order to ease utilisation the SSM/I+MERIS product
is distributed on a 0.5°x0.5° grid, with the MERIS product being averaged to match the lower
spatial resolution. On request, the product can be provided with 0.05°x0.05° spatial resolution
by oversampling the SSM/I product over ocean. Also on request, the product can be provided with a
cloud mask applied to the SSM/I data. The product is available as a daily composite or as monthly
mean. The water vapour of the atmosphere is vertically integrated in a column from surface to 200 hPa,
and given in units of kg/m². Both, the SSM/I and MERIS data streams are processed independently and
combined afterwards by not changing the individual TCWV values and their uncertainties. The final
product utilises SSM/I data onboard two satellites from the Defense Meteorological Satellite Program
(DMSP), namely F13 and F14, for the period 2003 to 2008. The SSM/I L2 data set contains descending
data which is closer to the overpass times of ENVISAT with MERIS on board (10 am local time). It is
based on homogenised L1 data for four frequencies and for horizontal and vertical polarization
(Anderson et al., 2010, a precurcor of the SSM/I FCDR from CM SAF). The MERIS data stems from
ESA's 3rd reprocessing of the MERIS L1 archive. The TCWV retrieval is applied to swath-based,
normalized radiances in MERIS bands 13, 14 and 15 at 865 nm, 885 nm and 900 nm, respectively, while
the cloud screening procedure utilises the full set of MERIS radiances between 400 and 900 nm.