Light-time-iteration Light time iteration must be computed in a non rotating frame Reason: Consider earth-fixed frame: one would simply compute earth fixed coordinates at earlier time In non-rotating frame, rotation to inertial coordinates would be done at two different time (receiver when signal received; transmitted when signal transmitted Difference is rotation of earth on 60 msec. Rotation rate +460 m/sec: therefore difference is about 30 meters 04/01/02 12.540Lec14 Clock errors PRN 03 June 14) 800 Clock SA( Clock nosa (ns) 2000 400 200 162024 Time(hrs) 12.540Lec1404/01/02 12.540 Lec 14 9 Light-time-iteration • Light time iteration must be computed in a non￾rotating frame • Reason: Consider earth-fixed frame: one would simply compute Earth fixed coordinates at earlier time. In non-rotating frame, rotation to inertial coordinates would be done at two different time (receiver when signal received; transmitted when signal transmitted). • Difference is rotation of Earth on ~60 msec. Rotation rate ~460 m/sec; therefore difference is about 30 meters. 04/01/02 12.540 Lec 14 10 Clock errors -200 0 200 400 600 800 0 4 8 12 16 20 24 PRN 03 (June 14) Clock SA (ns) 1999 Clock NoSA (ns) 2000 Clock error (ns) Time (hrs)