Jim, Dave:
At 15:44:58 UTC (08:44:58 PDT) we received a timing error which only lasted for one second. The error was reported by the CNS-II independent GPS receivers at both end stations, they both went into the 'Waiting for GPS lock' error state at 15:44:58, stayed there for one second, and then went good. The IRIG-B signals from these receivers are being acquired by the DAQ (and monitored by GDS). The IRIG-B signals for the second prior, the second of the error, and the following two seconds (4 seconds in total) are shown below.
As can be seen, even though EX and EY both reported the error, only EX's IRIG-B is missing during the bad second.
The encoded seconds in the IRIG-B are shown in the table below. Note that the GPS signal does not have leap seconds applied, so GPS = UTC +18.
| Actual seconds | EX IRIG-b seconds | EY IRIG-b seconds |
| 15 | 15 | 15 |
| 16 | missing | 16 |
| 17 | 16 | 17 |
| 18 | 18 | 18 |
So EY was sequential through this period. EX slipped the 16 second by a second, skipped 17 and resynced at 18.
Summary: All problems were in CNS II GPS Channels at LHO. No problems were observed in the Trimble GPS Channels at either site, nor in the LLO CNS II Channels, with the exception of a change of -80ns in the LLO Trimble GPS PPSOFFSET a few seconds after the anomally (see below). It seems that both LHO CNS II Clocks simultaneously dropped from 10 to 3 satellites tracked for a single second. There is no channel recording the number of satellites locked by the Trimble clocks, but the RECEIVERMODEs at both sites remain at the highest level of quality, OverDeterminedClock (level 5 for the Trimbles) with no interruption at the time of the anomaly. It is unclear whether the LLO PPSOFFSET is causally related to the LHO event; the lack of other anomalous output from the LLO Trimble clock suggests that it is otherwise performing as intended. Descriptions of anomalous plots below. All anomalous plots are attached. Dilution of precision at BOTH LHO CNS II clocks skyrockets to 100 around the event (nominal values around 1) (H1:SYS-TIMING_X_GPS_A_DOP, H1:SYS-TIMING_Y_GPS_A_DOP). Number of satellites tracked by BOTH LHO CNS II clocks Plummets or two seconds from 10 to 3 (H1:SYS-TIMING_X_GPS_A_TRACKSATELLITES, H1:SYS-TIMING_Y_GPS_A_TRACKSATELLITES). In the second before the anomaly, Both of the LHO CNS II Clocks' RECEIVERMODEs went from 3DFix to 2DFix for exactly one second, as evidenced by a change in state from 6 to 5 in their channels' values (H1:SYS-TIMING_X_GPS_A_RECEIVERMODE, H1:SYS-TIMING_Y_GPS_A_RECEIVERMODE). The 3D Speed also spiked right around the anomaly for both LHO CNS clocks (H1:SYS-TIMING_X_GPS_A_SPEED3D, H1:SYS-TIMING_Y_GPS_A_SPEED3D). LHO CNS II Clock's 2D speeds both climb up to ~0.1 m/s (obviously fictitious) (H1:SYS-TIMING_X_GPS_A_SPEED2D, H1:SYS-TIMING_Y_GPS_A_SPEED2D). LHO Y-End CNS II Clock calculated a drop in elevation of 1.5m following the anomaly (obviously this is spurious) (H1:SYS-TIMING_Y_GPS_A_ALTITUDE). LHO X-End CNS II Clock thinks it dropped by 25m following the anomaly! I'm not sure why this is so much more extreme than the Y-End calculated drop (H1:SYS-TIMING_X_GPS_A_ALTITUDE). The Livingston Corner GPS PPSOFFSET went from its usual value of ~0+/-3ns to -80 ns for a single second at t_anomaly + 3s (L1:SYS-TIMING_C_GPS_A_PPSOFFSET). The GPS Error Flag for both LHO CNS II clocks came on, of course (H1:SYS-TIMING_Y_GPS_A_ERROR_FLAG, H1:SYS-TIMING_X_GPS_A_ERROR_FLAG)
Using my very limited knowledge of Windows administration, I have attempted to list the events logged on h1ecatc1 from 8:00 - 10:00 AM on Feb. 27 2017. Attached is a screenshoot of what was reported. I don't see anything at the time in question. However, there is a quite reasonable chance that there are other places to look that I am not aware of and/or I did not search correctly.
