Zenith total delay, atmoshperic water vapor content and zenith wet delay derived from gps (Global Positioning System) measurements by the Geoforschungszentrum Potsdam (GFZ) within the EUMETNET GPS water
The ZTD (mm) is the 0-level product of the GPS data processing. It should be used for assimilation purpose. The IWV (kg/m**2) is the 1-level product of the GPS data. The conversion from ZTD to IWV is