GPS Satellite Ephemeris Error Estimation using National Satellite Testbed (NSTB) Data Jun 1, 1996· Tsai , Y. J. , Chao , Y. C. , Walter , T. Changdon Kee , Enge , P. , Powell , D. , Parkinson , B. W. · 0 min read Last updated on Jun 1, 1996 Authors Changdon Kee Professor ← Generation of Ionospheric Error and Confidence Estimates for WAAS Jun 1, 1996 Quality Control Algorithms on Wide-area Reference Station for WAAS Jun 1, 1996 →