Paul S. Jorgensen

Abstract: The GPS Operational Control System (OCS) has five monitor stations located world-wide. These stations continuously track all satellites in view, and this raw tracking data is transmitted to the master control station at the Consolidated Space Operations Center (CSOC) for further real time processing. The data is stored on tape and is available for post processing as well. This paper discusses a variety of ways the tracking data can be analyzed to obtain useful information regarding Navstar satellite performance as well as the performance of the OCS itself. Satellite tracking by the monitor stations is quite complete, with continuous tracking of the p-code modulation of both the LI and L2 carrier frequencies, as well as continuous phase tracking of the carriers themselves. This allows for post processing in a variety of ways depending on the physical effect the analyst is trying to unravel. Carrier tracking is very precise with the tracking noise down in the region of a few millimeters. This low noise characteristic makes it possible to separate out the short term stability of the satellite's atomic frequency standard. Over the past years this has proven to be a most valuable use of the tracking data, Another use of the tracking data is to study the characteristics of the ionosphere at the monitor station. From both pseudo range (PR) and accumulated delta range (ADR) at both carrier frequencies, the fine grain structure of the total electron count (TEC) as the satellite passes over the monitor station can be obtained. The code tracking noise in making the PR measurements can be studied in some detail. One recent new approach to these studies allows us to separate multipath effects at the monitor stations from other noise sources. The OCS combines all the tracking data over 15 minutes to obtain a single value of pseudo range. To accomplish this it uses a technique called "ionospherically corrected, ADR smoothed pseudo range."
Published in: Proceedings of the 18th Annual Precise Time and Time Interval Systems and Applications Meeting
December 2 - 4, 1986
DuPont Plaza Hotel
Washington, DC
Pages: 251 - 264
Cite this article: Jorgensen, Paul S., "VARIOUS USES OF THE GPS OPERATIONAL CONTROL SYSTEM (OCS) TRACKING DATA," Proceedings of the 18th Annual Precise Time and Time Interval Systems and Applications Meeting, Washington, DC, December 1986, pp. 251-264.
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