NSF SAGE Facility MUSTANG metrics Web Service Documentation

This metric reports the middle amplitude value in counts of sorted amplitude values from a 24-hour window. This median is one measure of the central tendency of the amplitudes in a time series when values are arranged in sorted order. The median value itself always occurs as an amplitude value in the times series.

Like the mean, the median amplitude of a time series describes its static behavior. For a properly functioning instrument, it can echo a channel’s DC level and/or mass position. Sudden changes in median can indicate partial loss of differential output, particularly if the RMS variance suddenly decreases simultaneously. The median is less sensitive to outliers than the mean.

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 or IRIS PH5 archive

SEED Channel Types – ?H?, ?L?, ?N?, ?G?, ?P?, VM? | High Gain, Low Gain, Accelerometer, Gravimeter, Geophone, Mass Channels

1. Request 24 hours of data for a single channel.
2. Identify and report the median amplitude value for the requested data:
   

   For i=1,N samples in the time series x:
       y(i) = sort{x(i)}
       median = y(N/2)
   

value – median amplitude in counts
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)

Instrument response has not been removed.