Validation of integrated water vapor from OMI satellite instrument against reference GPS data at the Iberian Peninsula

This paper shows the validation of integrated water vapor (IWV) measurements retrieved from the Ozone Monitoring Instrument (OMI), using as reference nine ground-based GPS stations in the Iberian Peninsula. The study period covers from 2007 to 2009. The influence of two factors, - solar zenith angle (SZA) and IWV -, on OMI-GPS differences was studied in detail, as well as the seasonal dependence. The pseudomedian of the relative differences is −1 ± 1% and the inter-quartile range (IQR) is 41%. Linear regressions calculated over each station show an acceptable agreement (R2 up to 0.77). The OMI-GPS differences display a clear dependence on IWV values. Hence, OMI substantially overestimates the lower IWV data recorded by GPS (∼40%), while underestimates the higher IWV reference values (∼20%). In connection to this IWV dependence, the relative differences also show an evident SZA dependence when the whole range of IWV values are analyzed (OMI overestimates for high SZA values while underestimates for low values). Finally, the seasonal variation of the OMI-GPS differences is also associated with the strong IWV dependence found in this validation exercise.This work was supported by the Spanish Ministry of Economy and Competitiveness through project CGL2014-56255-C2. Manuel Antón thanks Ministerio de Ciencia e Innovación and Fondo Social Europeo (RYC-2011-08345) for the award of a postdoctoral grant (Ramón y Cajal). Support from the Junta de Extremadura (Research Group Grants GR15137) is gratefully acknowledged. Work at Universidad de Valladolid is supported by project CMT2015-66742-R. Work at Universidad de Granada was supported by the Andalusia Regional Government (project P12-RNM-2409) and the Spanish Ministry of Economy and Competitiveness and FEDER funds under the projects CGL2013-45410-R and “Juan de la Cierva-Formación” program. Work at SAO is supported by NASA’s Atmospheric Composition: Aura Science Team program (sponsor contract number NNX14AF56G). Work at Universidade de Évora is co-funded by the European Union through the European Regional Development Fund, included in the COMPETE 2020 (Operational Program Competitiveness and Internationalization) through the ICT project (UID/GEO/04683/2013) with the reference POCI-01-0145-FEDER-007690