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Discrepancy Detected In GPS Time
jones_supa writes that on Tuesday, 26th January, Aalto University's Metsähovi observatory located in Kirkkonummi, Finland, detected a rare anomaly in time reported by the GPS system (Google translation). The automatic monitoring system of a hydrogen maser atomic clock triggered an alarm which reported a deviation of 13.7 microseconds. While this is tiny, it is a sign of a problem somewhere, and does not exclude the possibility of larger timekeeping problems happening. The specific source of the problem is not known, but candidates are a faulty GPS satellite or an atomic clock placed in one. Particle flare-up from sun is unlikely, as the observatory has currently not detected unusually high activity from sun.
http://www.navcen.uscg.gov/?Do...
Actually GPS receivers on earth are in a constant state of being updated. Part of the transmission from the satellite includes a continuous update of the orbital data for the GPS constellation, and other related data. Also, in North America, the WAAS system downlinks atmospheric correction data in real-time so that the GPS receiver can compensate for changes in the ionosphere.
...si hoc legere nimium eruditionis habes...
Lots of folks on the time-nuts mailing list have GPS-based systems to maintain not only precision time, but also precision frequency standards, and many of them saw and recorded this one.
Reading this, I really feel like I'm living in the future:
"The automatic monitoring system of a hydrogen maser atomic clock triggered an alarm which reported a deviation of 13.7 microseconds."
-Styopa
As someone who works in GPS software, you see these kinds of off-by-miles readings from time to time. If it was one time and not constant, we already have software in place to ignore the anomalous reading.
Peter predicted that you would "deliberately forget" creation 2000 years ago...
The status of each SV is also part of the datastream, and all it takes to "turn off" an errant SV is to set the flag in the data stream that says it is unusable.
WAAS doesn't know about atmospheric corrections. What WAAS does is use a network of fixed ground stations that detect deviations in position and generate data to correct those deviations. The assumption is that the WAAS receiver isn't moving, so any deviations are from propagation errors. This is the same kind of thing that has been used by surveyors and other high accuracy GPS users for decades. At the highest level of accuracy it is called realtime kinematic GPS, and it uses both the correction data and actual carrier phase information to give centimeter level accuracy. There is also "differential", which makes use of the correction data to get multi-cm level accuracy. Both were very big issues when selective availability was on.
there really should be a way to correct time in a GPS satellite
1) Press and hold the Set Time button until the indicator lamp lights (5 seconds)
2) Press + or - until the correct time is reached
3) Release Set Time button.
Clock speeds are sensitive to the structure of the gravitational field. Maybe other aspects of the Universe.
GPS times have all sort of noise. Some geophysicists use this "noise" to figure things like the atmospheric temperature and density. The GPS signal wavefront bend slightly then. You can tomographically invert for spatial location of the travel time anomalies to locate temperature and density changes. There are papers on this every year at the American Geophysical Union meeting.
Microsecond size anonalies are huge and may have more mudane causes like software.
>Sure, you just have to update the configuration of all GPS devices on earth...
If only they were capable of receiving signals from some sort of satellite.
Oh yeah, don't do any root cause analysis or anything, just keep ignoring all those gravity waves jittering the clocks on our orbiting atomic clock satellite network :-P
I'm trying to teach myself to set people on fire with my mind... Is it hot in here?
It looks like the actual problem was a bad data upload; Specifically, some satellites were transmitting incorrect parameters for UTC offset correction. https://www.febo.com/pipermail... is the posting from a gentlemen at Meinberg that has the details. http://www.usno.navy.mil/USNO/... has more information about the time offset parameters (A0 and A1) and how they interact with GPS and UTC time.
According to another message (https://www.febo.com/pipermail/time-nuts/2016-January/095686.html), PRNs 2, 6, 7, 9, and 23 got hit. It is interesting to note that the satellite that was taken out of service this morning (PRN 32) is not in this list. It looks like the decommissioning of PRN32 was quite possibly scheduled (see http://gpsworld.com/last-block...), and even if not, a failure of that specific satellite could not have caused multiple satellites to start broadcasting incorrect offset data.
I'm really looking forward to the postmortem on this.