The Design Of Kalman Smoothers For Global Positioning Data

Measurements of clocks aboard Global Positioning System (GPS) satellites as well as GPS system time are made many times per day at time standards laboratories around the world according to a tracking schedule issued by the Bureau International des Poids et Mesures (International Bureau of Weights and Measures). We compute Kalman smoothed estimates of clocks in the standards labs to define a global time base, then compute Kalman smoothed estimates of GPS clocks against this time base. Biases in measurements repeated once per sidereal day produce apparent diurnal effects in the data. A composite time and frequency Kalman estimator is used here. This allows updates of clocks at time intervals less than one day while aliasing diurnal variations.