Summary
After hourly power spectral density (PSD) measurements are instrument-corrected, discrete period-power values for the day are binned into a probability density function (PDF) matrix. The number of PDF values that are lower than the Peterson New Low Noise Model (NLNM) (Peterson, 1993) for each discrete period are presented as a percentage of total PDF values.
Peterson, J, 1993, Observations and Modeling of Seismic Background Noise, U.S.G.S. OFR-93-322
Uses
An easy way to identify dead channels is to search for pct_below_nlnm values below than some threshold.
Data Analyzed
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 – ?H?, ?L?, ?N?, ?G?, ?P? | High Gain, Low Gain, Accelerometer, Gravimeter, Geophone | excluding very long period channels
Algorithm
- Request 24 hours of time series data for the current N.S.L.C.
- Calculate PSDs (see noise-psd help)
- Correct PSD curves for instrument response.
- Bin PSD values into a PDF matrix using existing period values and 1 dB bins.
- For each period in the matrix,
- Make a running count of power values lower than the NLNM,
- Divide the final count by the total number of values in the matrix and multiply this ratio by 100 to get percent:
pct_below_nlnm = 100 * ( PDF_matrix_values_below_NLNM / total_PDF_matrix_values )
Metric Values Returned
value – percentage of PDF values below the NLNM curve
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)
Notes
Instrument response has been removed.
