Summary
Data latency is the time in seconds between the acquisition of a sample in the field and the time that it was written to disk or memory at the IRIS DMC. It is measured once every four hours for all real time data. Data latency will be low, within seconds usually, whenever transmission from the station to the data center is unimpeded. The normal operating value for data latency is largely station-dependent, so it can vary widely. Channels with lower sample rates generally have longer data latencies since it takes longer to fill a telemetry packet.
Uses
Data latencies are always nonzero, but increase when data transmission is slow or delayed. They may be used to identify misconfiguration of the datalogger, a problem with communications equipment, or other problems that might delay the data from being written to the data center disk buffer.
Data Analyzed
Traces – one N.S.L.C (Network.Station.Location.Channel) per measurement
Window – zero; each measurement represents an instantaneous measurement
Data Source – IRIS BUD near-real time data cache
SEED Channel Types – All Time Series Channels
Algorithm
- For a specified N.S.L.C, request the current
- Td: acquisition time of the latest data sample,
- Ta: time this sample became available on disk or in memory at the DMC,
- Tm: time that the latency metric measurement is calculated.
- Calculate and report the data latency:
data_latency = Ta - Td
Metric Values Returned
value – data latency in seconds
target – the trace analyzed, labeled as N.S.L.C.Q (Network.Station.Location.Channel.Quality)
start – Tm: time that the latency measurement was taken (UTC)
end – same as start
lddate – date/time the measurement was made and loaded into the MUSTANG database (UTC)
Notes
Data that was not archived as real-time data will not have latency metrics. All data in the real time feeds have SEED quality indicators of ‘R’ or ‘D’.
