Abstract
The Atmospheric Infrared Sounder (AIRS) aboard the Aqua spacecraft launched in April 2002 is being used to provide vertical profiles of moisture and column-integrated precipitable water vapor (IPW.) NOAA’s Forecast Systems Laboratory operates a network of over 200 geodetic-quality Global Positioning System (GPS) receivers at fixed surface locations across the United States to determine IPW from the excess zenith-scaled signal delays induced by the presence of water vapor in the troposphere. The GPS IPW observations are accurate, precise to about 1 mm, and can be made under all meteorological conditions encountered to date. They are characterized by a small (20 km) footprint and are delivered every 30 minutes with less than 20 minutes latency. These data are shown to be an ideal resource with which to validate AIRS IPW retrievals and to provide a reliable constraint for the verification of AIRS vertical water vapor profiles using radiosonde observations. This paper describes the principle of measurement of GPS zenith delay, the identification of the residual zenith delay attributable to moisture, and the conversion of the moist delay to IPW. Standards for hardware and software for producing validation-quality observations are outlined. The extraction of a database of collocated AIRS and GPS IPW and radiosonde moisture profiles is described. Plans for statistical and case study analyses are discussed, and preliminary intercomparison results are presented.
© 2003 Optical Society of America
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