Ionospheric Delay Validation Using Dual Frequency Signal from GPS at GEO Uplink Subsystem (GUS) Locations

M. S. Grewal, W. Brown, S. Evans, P. Hsu, R. Lucy

Abstract:	Local ionospheric delay values are needed at GEO Uplink Subsystem (GUS) locations to use for compensation of the uplink signal. The downlink ionospheric delay is computed using a dual frequency receiver, and by measuring both L1 down and C down delays from the antenna to the receiver (in the cables, converters, and amplifiers). The errors in measuring these delays cause a bias in the resulting ionospheric delay calculations at the GUS locations. The objective of this paper is to estimate the composite downlink delays using GPS L1 and L2 signals and to use these to calibrate the GUS equipment delays. Raytheon has established that 3 to 4 GPS Satellites are passing through the GUS transmit/receive antenna beam at different times. The GUS transmit/receive antenna beam is a 7° cone to the Inmarsat-3 1.5 meter antenna dish. GPS satellites take 20-30 minutes to pass through this beam, and thereby during these times have the same ionospheric pierce point to the GEO. The ionospheric delay is computed using GPS data collected when the satellites pass through the antenna beam. This paper shows the algorithms and results of the ionospheric delay calibration calculated from field data collected at GUS locations. Composite downlink delays are validated at each GUS location using this technique.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	1429 - 1436
Cite this article:	Grewal, M. S., Brown, W., Evans, S., Hsu, P., Lucy, R., "Ionospheric Delay Validation Using Dual Frequency Signal from GPS at GEO Uplink Subsystem (GUS) Locations," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 1429-1436.
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