Precise Clock Solutions Using Carrier Phase from GPS Receivers in the International GPS Service

As one of its activities as an Analysis Center in the International GPS Service IGS, the Jet Propulsion Laboratory JPL uses data from a globally distributed network of geodetic-quality GPS receivers to estimate precise clock solutions, relative to a chosen reference, for both GPS satellites and GPS receiver internal clocks, every day. The GPS constellation and ground network provide geometrical strength resulting in formal errors of about 100 psec for these estimates. Some of the receivers in the global IGS network contain high quality frequency references, such as hydrogen masers. The clock solutions for such receivers are smooth at the 20-psec level on time scales of a few minutes. There are occasional daily to weekly shifts at the microsec level, symptomatic of receiver resets, and 200-psec-level discontinuities at midnight due to 1-day processing boundaries. Relative clock solutions among 22 IGS sites proposed as fiducials in the IGSBIPM pilot project have been examined over a recent 4-week period. This allows a quantitative measure of receiver reset frequency as a function of site. For days and sites without resets, the Allan deviation of the relative clock solutions is also computed for subdaily values of tau.