As the Aqua satellite moves along, the AIRS mirror scans a "swath" across the Earth's surface and directs infrared energy into the instrument. This energy is separated into wavelengths, which are transferred from Aqua to computers on the ground for additional processing. (Source: http://airs.jpl.nasa.gov

After almost four years, the last soundings in the final phase of the Atmospheric Infrared Sounder (AIRS) validation program were completed on May 14 at the ACRF Tropical Western Pacific locale. Since late July 2002, operators at the ACRF sites launched approximately 2600 radiosondes (or sondes) in support of validation studies for the AIRS instrument aboard the National Aeronautics and Space Administration’s Aqua satellite. The AIRS instrument measures the amount of infrared energy emitted from the atmosphere. These measurements are used to calculate vertical profiles of atmospheric temperature, humidity, and concentrations of greenhouse gases. Data from AIRS can also be used to reveal land and sea surface temperatures.

Sponsored by NASA, the special series of sonde launches were conducted in phases to sample the annual climate cycle at each ACRF site. Radiosonde flights were timed so that two radiosondes were in the air (one near the tropopause and one near the surface) when the Aqua satellite flew over the sites. The sondes were launched approximately 40 minutes apart. The aim was 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. Analyses to-date indicate excellent data returns, and researchers have already begun using the data.

Global water vapor distributions are important in the study of climate, so the accuracy of the instrumentation providing these data is very important. The data set obtained from this four-year effort will be used by scientists around the world to better understand weather and climate.