PRN22 Signal Anomaly

It has been reported over the last few days of 2010 that satellite PRN22 (G22, SVN 47) has had issues.

Essentially the satellite had an issue with its navigation signal in that the Differential Code bias had changed a whole lot! this meant that the P1C1 biases we were all applying to be able to mix the ‘C1′ and ‘P1′ measurements from the satellites Read more about the differential code bias issue.

After some investigation we finally found that indeed the P1C1 bias for SVN47 has changed from 0.05 ns to -2.6 ns, so from ~1.5 cm to about -80 cm. This huge change made all the G22 clock comparisons and combinations across the IGS contributing solutions very inconsistent for a few weeks until the situation was finally properly analyzed, studied and corrected.

In the end there had been an unreported issue in the satellite on 30 Oct 2010, the satellite was set unhealthy via the navigation message, and later unsuable via NANU 2010133 for a 37 hour period and after reactivation the P1C1 bias was ~2.7 ns off!! This appears to have been caused by the switch on-board the spacecraft to a backup signal generator unit since at the anomaly start a significant signal power reduction was observed of more than 10 dB-Hz , which after the outage was fine.

Our wonderful colleague in the IGS A. Hauschild (DLR) produced the following technical note with all the details of this event. Happy reading!

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