|
SVN 27, 19:35:23 UTC 10 March 1998 |
|
|
|
SVN 27, 19:35:23 UTC 10 March 1998 |
|
25 NSTB receivers (all dual-frequency) were able to track through the event, 8 receivers exhibited cycle slip or loss of lock at the onset of the event (19:35:23 UTC). The L2 carrier phase fluctuations on those receivers which maintained lock were exactly the same as the L1 anomaly. Further, the Doppler measurements followed the clock event. Consequently the pseudorange error seen by a dynamic platform would only be detectable using external information from a static reference station or RAIM (provided sufficient geometry). The carrier, code, and Doppler measurements from the two different types of receivers which maintained lock are qualitatively similar but have some quantitative differences at onset and termination of the event. Figures showing the NSTB observations of carrier phase, pseudorange, Doppler and Doppler rate are available.
We are currently investigating three similar candidate events on two different SVNs within a four day period. If additional events can be confirmed they may provide additional clues to the cause of the clock event. We are continuing our investigation to determine both the cause and frequency of this type of event.
This anomaly is distinct from the Block II outage reported in the paper by Cobb, et.al., presented at ION GPS '95, Palm Springs.
If you would like further information on our findings or have additional observations please contact Andrew Hansen or Todd Walter at Stanford.
