Total Column Water Vapor derived from OMI - Validation and Updates

The Collection 3 Ozone Monitoring Instrument (OMI) Total Column Water Vapor (TCWV) data generated by the Smithsonian Astrophysical Observatory (SAO)'s algorithm Version 1.0 and archived at the Aura Validation Data Center (AVDC) are compared with NCAR's ground-based GPS data, AERONET's sun-photometer data and Remote Sensing System (RSS)'s SSMIS data. Results show that the OMI data track the seasonal and inter-annual variability of TCWV for a wide range of climate regimes. During the period from 2005 to 2009, the mean (OMI - GPS) over land is -0.3 mm and the mean (OMI - AERONET) over land is 0 mm. For July 2005, the mean (OMI - SSMIS) over the ocean is -4.3 mm. The better agreement over land than over the ocean is corroborated by the smaller fitting residuals over land and suggests that liquid water is a key factor for the fitting quality over the ocean in the Version 1.0 retrieval algorithm. We find that the influence of liquid water is reduced using a shorter optimized retrieval window of 427.7 - 465 nm. As a result, the TCWV retrieved with the new algorithm increases significantly over the ocean and only slightly over land. We have also made several updates to the Air Mass Factor (AMF) calculation. The updated Version 2.1 retrieval algorithm improves the land / ocean consistency and the overall quality of the OMI TCWV dataset. The Version 2.1 OMI data largely eliminates the low bias of the Version 1.0 OMI data over the ocean and are 1.5 mm higher than RSS's "clear" sky SSMIS data in July 2005. Over the ocean, the mean of (Version 2.1 OMI - GlobVapour) is 1 mm for July 2005 and 0 mm for January 2005. Over land, the Version 2.1 OMI data is about 1 mm higher than GlobVapour when TCWV < 15 mm and about 1 mm lower when TCWV > 15 mm.