Noise at Digital Broadband Stations Derived from Near Real Time Data
The figure below shows an estimate of the PSD background noise levels at digital broadband stations for which data are retrieved continuously in near real time over the internet using the LISS, NRTS, and Comserv protocols. Contributing networks include the IRIS GSN as well as other US and international seismic network. The signal power in narrow frequency bands is calculated hourly from the rms amplitude of the LHZ (vertical) channel, and converted to a decibel deviation from Peterson's (1993) new low noise model. For each station, the hourly values for some time period are ranked. The background noise level is estimated as the recorded signal level not exceeded a small fraction of the time (for example, 10% of the time). Only stations for which a sufficient number of hourly values are available are included in the graph.
The figure below shows the data for the last two weeks and is automatically updated daily.
Power Spectral Density
Noise Levels at Different Periods
The table below gives the decibel noise level (in db) for each station in
several period bands. The stations are ordered according to their
average noise level in the period band 300-40 seconds. Each entry in the
table is color coded with reference to the New Low Noise Model (NLNM, Peterson, 1993):
navy, -6 db < value-NLNM < -3 db
blue, -3 db < value-NLNM < 3 db
aqua, 3 db < value-NLNM < 6 db
lime, 6 db < value-NLNM < 9 db
yellow, 9 db < value-NLNM < 12 db
orange, 12 db < value-NLNM < 15 db
red, 15 db < value-NLNM < 20 db
fuchsia, 20 db < value-NLNM < 25 db
silver, value-NLNM < -6 db, value-NLNM > 25 db
Black indicates that there was an insufficient number of data to calculate a noise level.
The table is based on data for the last two weeks and is automatically updated daily.
Text file with the underlying data