Validation of Atmospheric Water Vapor from Several Satellite Instruments Using GPS Measurements at Spanish Stations Under Cloud-Free Conditions

This work deals with the validation of integrated water vapor (IWV) products derived from the following satellite instruments: Global Ozone Monitoring Instrument (GOME-2), Moderate-Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites, Ozone Monitoring Instrument (OMI), Spining Enhanced Visible and InfraRed Imager (SEVIRI), Atmospheric Infrared Sounder (AIRS), and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). IWV data from GPS in nine ground-based stations located in the Iberian Peninsula are used as reference. The study period extends from 2007 to 2012, under cloud-free conditions. All satellite instruments showed a tendency to reduce IWV extreme values: low IWV is overestimated while high IWV is underestimated. As for the influence of solar zenith angle (SZA), Seasonal dependence is mainly due to the SZA and IWV typical values in each season. In general, in summer the tendency is to underestimate with low inter-quartile range (IQR) and in winter the trend is to overestimate with high IQR