Know the Earth…Show the Way NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Approved for Public Release NGA Case # NGA’s Role in GPS Barbara Wiley

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # Coauthors: David Craig Dennis Manning John Novak Randall Taylor Leonard Weingarth

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # Overview NGA’s GPS Mission WGS 84 GPS Monitor Station Network Network Assessment Clock Analysis Legacy Accuracy Improvement Initiative (L-Aii) Precise Ephemeris Earth Orientation Summary

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # NGA’s GPS Mission 30+ years of satellite tracking Precise orbits needed to produce precise positions From the Master Positioning, Navigation and Timing Plan: –NGA is responsible for: Services to support DoD navigation systems Maintenance of GPS fixed site operations Generation and distribution of GPS precise ephemerides

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # WGS 84 Reference Frame Reference Frame: Global network of control stations that binds an Earth-centered, Earth-fixed 3-D coordinate system to the earth Control Station Position Accuracy Transit (1 - 2 m) Jan 1987 G730 (~10 cm) Jun 1994 G873 (~5 cm) Jun 1997 G1150 (~1 cm) Jan 2002 Ensure the WGS 84 Reference Frame errors are negligible in the GPS ephemeris error budget

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # GPS Monitor Station Network GPS Wing (formerly Joint Program Office) designs and acquires the GPS space systems USAF operates and maintains the GPS constellation NGA provides data and analysis to USAF on GPS satellites referenced to WGS 84

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # Network Assessment High performance: Dual Redundancy

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # Clock Analysis

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # Legacy Accuracy Improvement Initiative (L-Aii) L-Aii included: –Initial addition of 6 of NGA’s GPS monitor stations to the OCS Kalman filter –Model improvement to the OCS Kalman filter Results: –OCS has visibility of all satellites at all times –44% improvement to the ZAOD orbits –10% improvement in SIS URE

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # NGA GPS Network Tracking Data Currently 8 stations sent in near-real-time to the GPS Master Control Station at Schriever AFB –Improves integrity monitoring All satellites in view of at least two stations > 99% of the time –Improves accuracy Most users accuracy on the ground is 3-10m depending on equipment and environment Most users received 5-10% accuracy improvement Remaining 3 NGA stations will be incorporated for more robustness

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # Coverage by GPS Monitor Stations Assumes a 10 degree elevation mask

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # NGA Precise Ephemeris for GPS is DoD Truth - Precise determination of where the satellites were - Precise GPS clock solutions - Used for precise positioning and system analysis

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # NGA Precise Ephemeris comparisons Retuning Retuning and new tropo model Range diff data from Phase Obs added Additional Tracking Stations Deployed L-Aii begins G1150 implemented

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # Mean Axis of Rotation Axis of Figure North Pole Earth Orientation Prediction   Earth Orientation is used by the GPS Master Control Station to transform between Earth fixed coordinates to Earth inertial coordinates.  The transformation accuracy directly affects GPS accuracy

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # Polar Motion

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # UT1-UTC

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # Summary NGA supports the GPS MCS With L-Aii, NGA’s role in GPS has changed Now an integral partner in real-time GPS accuracy and integrity Real-time operations NGA’s GPS Monitor Station Network maintained at a high standard GPS products available online –

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case # NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Know the Earth…Show the Way Approved for Public Release NGA Case #