The National Geospatial-Intelligence Agency (NGA), provides timely, accurate, and leading edge Global Positioning System (GPS)-based products, with technical support & analysis to the Department of Defense (DOD), U.S. Intelligence Community (IC), and the broader scientific community. NGA has a global network of GPS monitor stations which defines the WGS 84 reference frame which GPS uses. NGA provides GPS data products, analysis, and GPS monitor station data, in real-time, to the USAF for inclusion in their orbit determination process which is then broadcast by the GPS constellation. In this way, NGA directly increases GPS accuracy and integrity for all GPS users. NGA determines the official DOD precise orbits for the GPS constellation which is needed for precise positioning. NGA also has the capabily to compute the orbits of other satellites using both doppler and host vehicle techniques.
NGA has these primary functions in the GPS area:
- GPS Monitor Station Network: the GPS division personnel manage NGA's GPS Monitor Station Network (MSN) which consists of 13 NGA worldwide GPS monitor stations. The MSN Control Center (MSNCC) is staffed 24x7x365 and provides real time monitoring, data collection, & quality review. This data is provided to the USAF in near real-time in support of their command and control of the GPS constellation.
- GPS Precise Ephemeris and Related Products: the GPS division personnel process daily satellite data from NGA, USAF, and International GPS Service GPS monitor stations. This data is used to produce daily precise (cm level to WGS 84) ephemerides (orbit), predicted orbits, and clock solutions for all GPS satellites. In support of the DOD and NASA test ranges (C-band radar community), we produce a daily Radar Calibration (RADCAL) and Defense Meteorological Satellite Program (DMSP) satellite ephemeris using up to 21 Doppler tracking stations.
- Earth Orientation: the GPS division produces and provides twice-weekly Earth Orientation Parameter Prediction (EOPP) to the USAF. This relates the inertial reference frame of the satellite to the earth's fixed reference frame and is an essential part of the accuracy of GPS. This data references USNO products.
For NGA GPS products, related documents, and additional information and resources, please visit http://earth-info.nga.mil/GandG/sathtml/.