Ionosphereic Studies from GPS Measurements on Board of the Portuguese Satellite PoSAT-1

Isabel Osorio, Jose Pereira Osorio and Jose Manuel Rebordao

Abstract:	The Computerized Tomography (CT), to produce an image of the electron density in the ionosphere, is a technique now being applied to radio studies of the ionosphere. This technique requires that the measured data be the line integral through the medium of the unknown parameter. It was shown that the ionospheric Total Electronic Content (TEC) met this requirement. Several methods, based on GPS code and carrier phase measurements, have been developed for ionospheric TEC evaluations. Most of them are based on processing measurements from dual frequency GPS receivers. The directions of those evaluations are, then, all from the Earth. In order to reach other directions, it is necessary to use radio signal sensors outside the Earth as, for instance, in a LEO satellite. The Portuguese satellite PoSAT-1 has implemented on board a GPS experiment mainly for precise time keeping on board and for autonomous navigation. For this purpose, a GPS sensor, based on a Trimble TANS II single frequency receiver, and a GPS signal antenna were included in the satellite payload. PoSAT-1 is in a sun-synchronous polar orbit, at a mean altitude of 810 km, so, still inside the ionosphere. The main idea of this work is to use GPS signals for TEC evaluation. The data for such computations are the codephase measurements smoothed by Doppler measurements, recorded on board, twice an orbit, during 15 minutes, at a small rate of acquisition (0.5s). The knowledge of precise orbits for PoSAT-1 and of the receiver clock error and, also, the use of precise ephemeris for GPS satellites, allow that the measurements from GPS satellites with low elevations in the PoSAT-1 horizon can be used for TEC evaluation along the signal path. Some of the directions along which the observations were processed are impossible to be defined from Earth, as it will be shown. In this paper the methods used and the results obtained with real data will be presented.
Published in:	Proceedings of the IAIN World Congress and the 56th Annual Meeting of The Institute of Navigation (2000) June 26 - 28, 2000 The Catamaran Resort Hotel San Diego, CA
Pages:	602 - 606
Cite this article:	Osorio, Isabel, Osorio, Jose Pereira, Rebordao, Jose Manuel, "Ionosphereic Studies from GPS Measurements on Board of the Portuguese Satellite PoSAT-1," Proceedings of the IAIN World Congress and the 56th Annual Meeting of The Institute of Navigation (2000), San Diego, CA, June 2000, pp. 602-606.
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