Summary
This metric counts the times this clock flag is set from 0 (default) to 1 in the fixed section of the miniSEED header. A flag value of 1 indicates that the GPS has locked with enough satellites to obtain a time/position fix. Not all dataloggers set this flag.
PH5-format data does not include miniSEED flag information; this metric will always return a value of 0 for data in the IRIS PH5 archive.
Uses
This metric can be used to identify dataloggers with faulty GPS clocks and data days with questionable timing. Lack of a GPS lock does not necessarily mean that a datalogger’s internal clock is known to have drifted significantly from GPS time. Some modern VCXO clocks may not drift significantly for days after their last GPS lock.
If using this metric with the rrds service, be aware that a value of 0 (zero) can either mean that
the datalogger detected 0 instances of this condition, or
the datalogger does not set this flag, so it is unknown whether or not this condition occurred.
Unless all channels in an rrds request are known to set this flag, requesting data with a count greater than 0 may omit data for which GPS locks occurred.
Data Analyzed
Traces – one N.S.L.C (Network.Station.Location.Channel) per measurement
Window – 24 hours starting at 00:00:00 UTC
Data Source – IRIS miniSEED archive
SEED Channel Types – ?H?, ?L?, ?N?, ?G?, ?P?, VM? | High Gain, Low Gain, Accelerometer, Gravimeter, Geophone, Mass Channels
Algorithm
- Request 24 hours of data for a single N.S.L.C.
- Count and report the number times this binary flag is set to 1.
Metric Values Returned
value – number of times this flag is set to 1 that day
target – the trace analyzed, labeled as N.S.L.C.Q (Network.Station.Location.Channel.Quality)
start – beginning of the data day requested (00:00:00 UTC)
end – end of the data day requested (truncated as 23:59:59 UTC)
lddate – date/time the measurement was made and loaded into the MUSTANG database (UTC)
Notes
Not all dataloggers set this flag. For those that do not, a value of 0 does not necessarily mean that the GPS clock is unlocked.
