Gps Radio Occultation Technique To Monitor The Earth's Atmosphere

Global Positioning Systcm(GPS) Is quickly achlcving a routine prcscnce In space for basic utility functions of real time onboard state determination, precise time and frequency transfer, and modcrate precision attitude determination, and Is likely to be a good choice for many future Earth satellites of those tasks. As a ramification of such disciplines as GPS surveying technique and Meteorology, GPS meteorology is becoming an emerging subject, which includes both space-borne GPS radio occultation technique and ground-based GPS technique. Space-borne GPS for Earth science is in the exiting early phase of invention, with promising developments underway in geodesy, climatology, weather modeling, and ionospheric imaging. By the way, occultation technique was pioneered by JPL and Stanford University oi抏r 30 years ago for study of planetary atmospheres and ionospheres.We describe in this paper a particular remote-sensing application that is well suited to the combination of space-borne GPS and occultation technique the space-borne GPS radio occultation technique. Since the end of 1980?s, this technique has been noticed in application to meteorological researches. Radio occultation studies of the terrestrial atmosphere are now possible through use of signals transmitted by GPS satellites and received by one or more other satellites in low Earth- orbit(LEO), high-vertical-resolution profiles for atmospheric parameters can be retrieved from observations obtained when the radio path between transmitter and receiver traverses the Earth?s atmosphere. On April 3, 1995, the launch of the first experimental LEO satellite MicroLab 1 opened a new ear of GPS meteorology(GPS/MET), and its experimental data and achievements proved its potential scientific roles in probing the Earth atmospheric profiles. In this paper, a study has been performed to analyze several aspects of LEO satellite precise orbit determination using the GPS. Consequently, it is briefly and systematically introduced how to apply the GPS radio occultation technique to measure and monitor the vertical profile of global atmospheric refractive index, temperature, pressure and moisture. Preliminary results from the GPS/MET experiment are also outlined. Long sequential occultation data at a ground grazing point will definitely benefit the meteorological and atmospheric research applications of LEO satellite. A new idea of commensurate LEO satellite to control grazing points on the Earth surface was proposed in this paper. Results from simulating computation have shown that in the period of about 60-200 days or longer the drifts of grazing points on earth surface could be controlled to be less than 100km.