A Comparison of Columnar Water Vapor Retrievals Obtained with Near-IR Solar Radiometer and Microwave Radiometer Measurements

A simple two-channel solar radiometer and analysis technique have been developed for sensing atmospheric water vapor via differential solar transmission measurements in and adjacent to the 940-nm water vapor absorption band. A prototype solar radiometer developed for the National Oceanic and Atmospheric Administration (NOAA)/Environmental Research Laboratory underwent trial measurements near Boulder, Colorado, and during the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment Phase II cirrus intensive field observation program (Coffeyville, Kansas). These measurements provided the convenient opportunity to compare solar radiometer water vapor retrievals with those obtained using NOAA microwave radiometers. The solar radiometer and microwave radiometer retrievals were found to agree to within 0.1 cm most of the time and to within 0.05 cm the majority of the time, yielding a percent difference in the retrievals generally within 10%. Radiosonde soundings, when available, were also found to generally agree with the microwave and solar radiometer retrievals within 0.1 cm.