Validation of AIRS retrieved products with operational and dedicated radiosondes

Height resolved temperature and water vapor are two of the core products produced by the Atmospheric Infrared Sounder (AIRS) experiment, orbiting on NASA’s EOS Aqua spacecraft since May 2002. Primary objectives of AIRS are measurement uncertainties comparable to or better than current radiosondes: 1 K in 1 km layers for temperature and 20% in 2 km layers for water vapor in the troposphere. These quantities, along with properties of clouds, the surface, and minor gases, are simultaneously retrieved from directly observed infrared and microwave radiances. The resulting fields have a spatial resolution of about 50 km within an obit swath 1500 km wide. The AIRS system of instruments and software yields about 300,000 daily sets of temperature and humidity profiles. This is roughly two orders of magnitude larger than the current set of operational radiosondes, and includes supplementary information about minor gases, clouds and the surface. Profiles of temperature and humidity are validated through comparison with dedicated and operational radiosondes. Several factors complicate this comparison, including limited information about water vapor above 400 hPa, a highly variable water vapor distribution, space and time mismatches between sondes and AIRS, a retrieval system whose uncertainties increase with cloudiness, and, strong correlation between clouds and water vapor. Despite these challenges, a clear picture is emerging of AIRS retrieval performance relative to radiosondes: profile quantities that meet, or even exceed, the measurement system specifications described above. We describe the analyses used to reach that conclusion, and present some estimates of AIRS performance over a variety of oceanic locations. We also show some preliminary results for the more challenging conditions encountered over land.