ANALYSIS AND VALIDATION OF GPS MET DATA IN THE NEUTRAL ATMOSPHERE/

The Global Positioning System/Meteorology (GPS/MET) Program was establ ished in 1993 by the University Corporation for Atmospheric Research ( UCAR) to demonstrate active limb sounding of the Earth's atmosphere us ing the radio occultation technique. The demonstration system observes occulted GPS satellite signals received by a low Earth orbiting (LEG) satellite, MicroLab-1, launched April 3, 1995, The system can profile ionospheric electron density and neutral atmospheric properties, Neut ral atmospheric refractivity, density, pressure, and temperature are d erived at altitudes where the amount of water vapor is low, At lower a ltitudes, vertical profiles of density, pressure, and water vapor pres sure can be derived from the GPS/MET refractivity profiles if temperat ure data from an independent source are available. This paper describe s the GPS/MET data analysis procedures and validates GPS/MET data with statistics and illustrative case studies. We compare more than 1200 G PS/MET neutral atmosphere soundings to correlative data from operation al global weather analyses, radiosondes, and the GOES, TOVS, UARS/MLS and HALOE orbiting atmospheric sensors. Even though many GPS/MET sound ings currently fail to penetrate the lowest 5 km of the troposphere in the presence of significant water vapor, our results demonstrate 1 de grees C mean temperature agreement with the best correlative data sets between 1 and 40 km, This and the fact that GPS/MET observations are all-weather and self-calibrating suggests that radio occultation techn ology has the potential to make a strong contribution to a global obse rving system supporting weather prediction and weather and climate res earch.