Abstract

Atmospheric limb sounding technique, making use of the radio signals transmitted by Global Positioning System (GPS), has emerged as a promising approach for global meteorological observations. As demonstrated by the proof-of-concept GPS Meteorology (GPS/MET) experiment, the GPS radio occultation ... Show moreAtmospheric limb sounding technique, making use of the radio signals transmitted by Global Positioning System (GPS), has emerged as a promising approach for global meteorological observations. As demonstrated by the proof-of-concept GPS Meteorology (GPS/MET) experiment, the GPS radio occultation (RO) sounding data are of high accuracy and high vertical resolution. Results from recent GPS RO missions of CHAMP and SAC-C confirm this assessment. In late 2005, the joint U.S.-Taiwan COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) mission will be launched and is expected to collect approximately 3,000 RO soundings per day. These data will be available in near real-time for global weather analysis and prediction. The raw measurements of GPS RO soundings are phase and amplitude of radio signals. It takes a number of steps to reduce the data to the traditional meteorological variables of temperature, pressure and water vapor. Because of the ray traversing geometry, the GPS RO data have unique "pencil-like" measurement characteristics, which is very different from the point measurement of a radiosonde or an "area-average" measurement of a microwave sounder. To assimilate GPS radio occultation data effectively into a weather prediction model, one needs to correctly process the data and to properly account for the measurement characteristics and measurement errors. In this paper, we will discuss scientific and technical issues related to the assimilation of GPS radio occultation data into weather prediction models. Show less