Stand AloneGPS Position Errors

James R. ClynchDepartment of OceanographyNaval Postgraduate School

Monterey, CA 93943

clynch@nps.navy.mil

Several Notes on GPS AccuracyCan Be Found At:

www.oc.nps.navy.mil/~jclynch

SOLUTION TYPES

Navigation

Pseudorange PositonPhase VelocityDynamics Built InKalman Estimator ( 8 State)

Relative Navigaton

Differential Range Correction eash SVStandard FormatsSolution as in Navigation1-2 m Broad Area Systems10 cm – 50 cm Special Purpose Systems

Kinematic

Differential PhaseDetermine Phase Bias (Ambiguity Resolution)Dynamic / Must Keep 4 or More Common Satellites3 – 10 cm

Tracks Taken On 9 Different DaysRaw Data on Left, Adjusted Data on Right

Orbit Estimation Considerations

Force ModelGravity 8x8 to 12x12Solar and Lunar GravitySolid Earth TidesRadiation Pressure(Thrusts, Momentum Dumps)

FrameDone in Inertial FrameLunar-Solar, Planetary precessionNutationPolar MotionUT1-UTC (irregular rotation rate)Spacecraft Center Gravity Offset

From Antenna Phase Center

Measurement AdjustmentsIonospheric - two frequency adj.Tropospheric - Saastamoinen Dry

Neill WetPeriodic Relativistic TermsStation Displacement

Earth TidesCrustal Motion

One arc second is about 30 m