Since 2002, ARM operations staff have been conducting a phased series of special radiosonde launches at all the ARM permanent sites to support validation studies for the Atmospheric Infrared Sounder (AIRS) instrument aboard the National Aeronautics and Space Administration’s (NASA) Aqua satellite. The AIRS instrument was designed to make highly accurate measurements of air temperature, humidity, clouds, and surface temperature—important components for climate simulations. On October 16, 2007, staff at the ARM Tropical Western Pacific site in Nauru launched the final set of sondes in Phase 6 of this effort. Final launches at the Southern Great Plains site were completed in September and at the North Slope of Alaska locale in early October. The validation effort is now complete.

Sponsored by NASA, the special series of sonde launches was conducted in phases to sample the annual climate cycle at each ARM site. Radiosonde flights were timed so that two radiosondes—launched approximately 40 minutes apart—were in the air (one near the tropopause and one near the surface) when the Aqua satellite flew over the sites. The aim is to (a) provide in situ validation data for the development and testing of water vapor retrievals obtained from the AIRS sensor aboard Aqua and (b) demonstrate and quantify the accuracy of AIRS water vapor retrieval algorithms.

Originally intended to end in 2006, NASA requested continued validation support through FY2007 to also make flights coordinated with overpasses of the Infrared Atmospheric Sounding Interferometer (IASI). This instrument became operational on the European Space Agency’s MetOp-A satellite in July. Like AIRS, IASI measures the spectral distribution of atmospheric radiation to provide accurate measurements of air temperature and humidity. During the course of the six AIRS phases, approximately 3000 extra radiosondes were launched to support these validation efforts, and analyses to-date indicate excellent data returns for achieving the science objectives.