Error analysis for the Global Positioning System: Difference between revisions

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=== Sagnac distortion ===

GPS observation processing must also compensate for the [[Sagnac effect]]. The GPS time scale is defined in an [[inertial]] system but observations are processed in an [[ECEF|Earth-centered, Earth-fixed]] (co-rotating) system, a system in which [[Relativity of simultaneity|simultaneity]] is not uniquely defined. A coordinate transformation is thus applied to convert from the inertial system to the ECEF system. The resulting signal run time correction has opposite algebraic signs for satellites in the Eastern and Western celestial hemispheres. Ignoring this effect will produce an east–west error on the order of hundreds of nanoseconds, or tens of meters in position.<ref>Ashby, Neil [http://www.ipgp.fr/~tarantola/Files/Professional/GPS/Neil_Ashby_Relativity_GPS.pdf Relativity and GPS]. [[Physics Today]], May 2002.</ref>

== Natural sources of interference ==