AF/NGA GPS Monitor Station High-Performance Cesium Frequency Standard Stability 2005/2006: From NGA Kalman Filter Clock Estimates

Dennis M. Manning

Abstract:	Both the National Geospatial-Intelligence Agency (NGA) and the United States Air Force (USAF/AF) operate a worldwide network of GPS monitoring stations that utilizes high-performance cesium frequency standards (CFSs) and geodetic quality GPS receivers. The USAF stations are somewhat equatorial, whereas the NGA stations are primarily in both the Northern and Southern Hemispheres. The NGA Monitor Station Network (MSN) has been in operation since 1983 and the operation in St. Louis currently monitors all the NGA stations on a 24/7 basis. The USAF operates their stations in a similar manner. The NGA monitor station CFSs are located in non-laboratory environments and in some instances, are logistically challenging. With the onset of the Department of Defense GPS Accuracy Improvement Initiative (Aii), the NGA monitor station cesiums, along with the associative electronics, must be monitored more frequently for quality control. Aii involves the USAF Operational Control Segment (OCS), at Schriever AFB, to incorporate at first a subset (six) of the NGA monitor stations in real-time processing to improve the quality of the broadcast ephemeris and clock parameters. Two more NGA monitor stations were added in the early fall 2006. The remaining three are scheduled to be added during the fall/winter 2006 timeframe. The addition of the NGA stations will expand the network coverage to allow all GPS satellites to be monitored without any gaps. This paper is a summary of the stability of the USAF and NGA MSN cesiums, along with other upgrades during the year 2005 and fiscal year 2006, using the Kalman Filter clock estimate data computed daily at the NGA facility in St. Louis. The quality of the CFSs shown and summarized in this report are from six AF and eleven NGA monitor stations, of which eight NGA stations have been added to the OCS estimation process under Aii. Results show that the AF/NGA configuration of CFS has maintained the industry standards for high performance cesiums. This gives the AF/NGA GPS program some of the most reliable monitor station clock data to support current and future GPS navigation systems.
Published in:	Proceedings of the 38th Annual Precise Time and Time Interval Systems and Applications Meeting December 7 - 9, 2006 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	137 - 152
Cite this article:	Manning, Dennis M., "AF/NGA GPS Monitor Station High-Performance Cesium Frequency Standard Stability 2005/2006: From NGA Kalman Filter Clock Estimates," Proceedings of the 38th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, December 2006, pp. 137-152.
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