GPS/LEO Rapid Orbit Determination in Support of GPS Meteorology: Status and Future Plans

Abstract

GPS meteorology has a potential of seamless sounding of refractivity from LEO (low earth orbit) orbit altitude to near Earth surface, and vertically above the land-based receivers. In GPS occultation technique, the LEO position and velocity are required with accuracy of 10 cm and 0.1 mm/s RMS, respectively {[}Rocken et al., 1997; Zhao, 1998) to retrieve temperature profile with accuracy of 1K or better for higher altitudes. Even more stringent, from the operational standpoint, might be the need for near-real time retrieval of atmospheric profiles for potential contribution of GPS/LEO data to operational weather forecasting. The Ohio State University is an IGS LEO/GPS Associate Analysis Center participating in the IGS LEO Pilot Study Project, studying the orbit determination in near real-time, to support atmospheric data retrieval from GPS/LEO occultations. In addition, the Center is a part of the NSF/UCAR SuomiNet GPS network, also supported by NOAA and Natural Resources Canada. This is a 16-station network, currently under implementation, located primarily along the shoreline of the Great Lakes, including Lake Erie shorelines bordering the State of Ohio. The stations, equipped with dual frequency GPS receivers and meteorological sensors, will be collocated with the NOAA tide gauges, and will support not only the atmospheric research but also the accuracy improvement of the International Great Lakes Datum (IGLD). The primary objective of this paper is to present the proposed procedures and techniques for the Center's operations that will support the experiments in orbit determination, occultation data processing, as well as atmospheric data retrieval from LEO. In particular, we will focus on GPS/LEO precise orbit determination (POD) with special emphasis on triple difference (TD) kinematic approach. The triple difference technique, successfully applied to GPS POD, has already been presented by Grejner-Brzezinska {[}1995], Goad et al. {[}19961 and Kwon {[}1997]; we have now extended this method to LEO POD. Preliminary results of kinematic POD for the CHAMP satellite, and the atmospheric parameter retrieval using GPS/MET data are also discussed.