This metric reports the lowest timing quality as recorded by the data logger for the Global Seismographic Network (GSN) data. The timing quality for the current Quanterra Q330HR digitizers is determined from miniSEED Blockette 1001, field 3 values. The timing quality for earlier data loggers is mapped to Quanterra Q330HR conventions for consistent values across time. These contributed measurements are performed at the Albuquerque Seismological Laboratory (ASL) on data that is housed there and also archived at the IRIS DMC.
These measurements are stored with the quality code ‘Q’.
This metric provides users the opportunity to identify data where the timing quality of GSN stations could be lower than the very high timing standard maintained by most GSN data (i.e. < 10ms). For the current generation of data logger in the GSN (Quanterra Q330HR), timing is ensured when the clock quality factor, encoded in SEED Blockette 1001, is above 60%. A value below 60% indicates that if the data is going to be used for an application that needs very precise timing, then the data records of interest should be analyzed for their particular timing quality values.
Trace – one N.S.L.C (Network.Station.Location.Channel) per measurement
Window – 24 hours starting at 00:00:00 UTC
Data Sources – IRIS miniSEED archive for Q330HR digitizers, ASL and Project IDA database for earlier data loggers
SEED Channel Types – [BEHLSV]H?, [BEHLSV]N?, [BEHLSV]G? | High Gain, Low Gain, Accelerometer, Gravimeter
For data recorded by Quanterra Q330HR digitizers (post-2009):
- Request 24 hours of data for a single N.S.L.C.
- Read the Blockette 1001 Field 3 timing quality values, and return the minimum value
For earlier generations of data loggers used in the GSN, differing mappings of clock quality were employed. In order to produce a metric that was uniform across the GSN network’s lifetime, the clock quality values produced by earlier data loggers were remapped in this metric to conform to the Q330HR’s present convention. Users examining older (pre-2009) GSN data will find the Blockette 1001 values may not match the value in this metric.
For data recorded by Quanterra Q680 digitizers, gsn_timing values will usually conform to the minimum Blockette 1001 value for the day. However, there are special cases where additional timing quality knowledge is available and used to modify the gsn_timing output. For older IRIS/IDA data loggers that did not record Blockette 1001 values, the gsn_timing metric is determined by time of last clock lock and drift rate in a manner that closely matches the Q330HR.
Details of the GSN data loggers and their timing quality will be provided in an upcoming scholarly article, reference to be provided.
value – The minimum timing quality value for this day, expressed as a percent.
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)
Please contact James Holland (email@example.com) for questions about this metric. This GSN metric is part of the Data Quality Analyzer and was developed as a collaboration with IRIS, the USGS, and Project IDA.