Applications of GPS Radio Occultation Sounding Technique to Weather and Climate and the FORMOSAT-3/COSMIC Mission

The atmospheric limb sounding technique making use of radio signals transmitted by the Global Position System (GPS) has emerged as a promising approach for global atmospheric measurements. As demonstrated by the proof-of-concept GPS Meteorology (GPS/MET) experiment and more recently by the CHAMP and SAC-C missions, the GPS radio occultation sounding data are of high accuracy and high vertical resolution. In early 2006, the joint U.S.-Taiwan FORMOSAT-3/COSMIC mission will be launched and is expected to collect up to 2,500 radio occultation soundings per day. These data will be available in near real-time for global weather analysis and prediction and for climate monitoring.

Radio occultation measures phase and amplitude of the microwave signals emitted from GPS. These signals are inverted to obtain profiles of signal bending, atmospheric refractivity, pressure temperature and water vapor. The main purpose of the upcoming FORMOSAT-3/COSMIC mission is to demonstrate the value of these radio occultation products for weather forecasting, climate monitoring, ionospheric research and space weather prediction. This presentation will provide an overview of the FORMOSAT-3/COSMIC program, and its applications to weather and climate. Results from the recently implemented open-loop tracking technique will be shown. This technique allows for radio occultation soundings to be taken very near to the surface and considerably improve the penetration of the GPS RO soundings in the lower troposphere. For further information on the FORMOSAT-3/COSMIC, please refer to http://www.cosmic.ucar.edu/.