NGA GPS monitor station high-performance cesium frequency standard stability: from NGA Kalman filter clock estimates

The National Geospatial-Intelligence Agency (NGA) operates a worldwide network of GPS monitoring stations that utilizes high-performance cesium frequency standards (CFS) and geodetic quality GPS receivers. The NGA monitor station network (MSN) has been in operation for almost 20 years and has recently moved to a 24/7 operation. The NGA monitor stations CFS 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 air force operational control segment (DCS), at Schriever AFB, to incorporate a subset of the NGA monitor stations in real-time processing to improve the quality of the broadcast ephemeris and clock parameters. The addition of these stations will also 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 NGA MSN cesiums using one year (52 weeks) of Kalman filter clock estimate data computed daily at the NGA facility in St. Louis. The quality of the CFSs to be shown and summarized in this report is from eleven NGA monitor stations, which are to be added to the OCS estimation process under Aii. Results show that the NGA configuration of CFS has maintained the industry standards for high performance cesiums. This gives the NGA GPS program some of the most reliable monitor station clock data to support current and future GPS navigation systems