SAGE Facility MUSTANG metrics Web Service Documentation

This metric computes the coherence between two co-located broadband sensors using a gamma-squared coherence. It compares 24 hours of data from like components (e.g. vertical to vertical). The coherence values are averaged over different frequency bands. 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’.

When the coherence between both sensors is high this suggests both sensors are seeing similar signals. Low coherence could be the result of instrumentation problems, local vault tilt, timing or orientation errors.

Note that asl_coherence, which only has measurements for the LH channels of IC, II, IU and US networks, is currently unrecognized by rrds.

Traces – two rotated N.S.L.Cs (Network.Station.Location.Channel) from different co-located sensors per measurement
Window – 24 hours starting at 00:00:00 UTC
Data Source – IRIS SEED archive

SEED Channel Types – LH? | High Gain

• Request LH data location codes 00 and 10.
• Using the current metadata, rotate the data into three streams: Z, N, and E.
• Calculate the coherence between the 00 and 10 location code for each of the three rotated data streams by estimating the Welch cross-power (Pxy) using 13 overlapping segments, zero padded to a power of 2, with 75% overlap. We remove the mean, a linear trend, and apply a 10% cosine taper.
  

  Cxy = |Pxy|^2/(Pxx*Pyy) 
      where Pxy is the cross-power of x (00) and y (10) and Pxx and Pyy are the cross-power of x with x and y with y, respectively.
  

• Average the coherence over four different power bands: 4 to 8 s period, 18 to 22 s period, 90 to 110 s period, 200 to 500 s period.

PB4to8sec – the average coherence over 4 to 8 seconds.
PB18to22sec – the average coherence over 18 to 22 seconds.
PB90to110sec – the average coherence over 90 to 110 seconds.
PB200to500sec – the average coherence over 200 to 500 seconds.
target = NN.SSSSS.00:10.CCC.Q.
start – beginning of the data day requested (requested day 00:00:00)
end – end of the data day requested (next day 00:00:00)
lddate – date/time the measurement was made and loaded into the MUSTANG database (UTC)

Please contact James Holland (jholland@usgs.gov) with questions about this metric.
This ASL metric is part of the Data Quality Analyzer.