The GSN Dead Channel Metric is a variant of dead channel detection based on a low signal threshold in the microseism range of 4 to 8 seconds period. The values shown with this metric indicate a TRUE or FALSE condition, depicted by a ‘1’ or ‘0’ value respectively. A TRUE value, meaning that the channel is dead, occurs when the median probability value of a day’s worth of instrument-corrected power spectral density (PSD) values are 5 dB below the New Low Noise Model (NLNM) when averaged over the 4 to 8 second band.
A ‘1’ value is a good indication of a channel that is not responding to ground motion signals. This can also appear where the response metadata for the channel is faulty. Using a boolean value for dead_channel_gsn allows users to scale metrics such as percent_availability whenever a channel is dead. For instance, multiplying percent_availability by 0 whenever dead_channel_gsn is TRUE is one way to prevent dead channels within the archive from being included as “available” in reports. Using rrds to request broadband channels with dead_channel_gsn=0 should omit dead channels from the request.
Traces – one N.S.L.C (Network.Station.Location.Channel) per measurement
Window – up to 24 hours depending on the completeness of data
Data Source – IRIS miniSEED archive or IRIS PH5 archive
SEED Channel Types – [BCDFHLM]H? | High Gain
- Request N.S.L.C data having sample rate 1 SPS or greater.
- Generate the PSD matrix for the selected channel, midnight to midnight (as per McNamara, et. al.).
- Slice the PSD matrix, retaining values between 4 to 8 seconds period.
- Calculate the median power in dB at each bin frequency (4-8 seconds), writing results to a vector Y(x).
- Calculate the differences in median vector from the equivalent NLNM vector and take the average: mean[ NLNM – Y(x)].
- If the dB deviation from the NLNM is greater than 5.0, set dead_channel_gsn value = 1 (TRUE), else set value = 0 (FALSE):
value = '1': deviation from NLNM > 5.0 | '0':default
value – ‘1’ if TRUE (dead), ‘0’ if FALSE (ok)
target – the trace analyzed, labeled as N.S.L.C.Q (Network.Station.Location.Channel.Quality)
start – time of the first sample of time series data for that day in UTC
end – time of the last sample of time series data for that day in UTC
lddate – date/time the measurement was made and loaded into the MUSTANG database (UTC)
McNamara, D.E. and R.P. Buland, Ambient Noise Levels in the Continental United States, Bull. Seism. Soc. Am., 94, 4, 1517-1527, 2004.
Ringler, A.T., M.T. Hagerty, J. Holland, A. Gonzales, L.S. Gee, J.D. Edwards, D. Wilson, and A.M. Baker. 2015. The data quality analyzer. Comput. Geosci. 76, C (March 2015), 96-111. DOI=http://dx.doi.org/10.1016/j.cageo.2014.12.006