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DMC Transportable Array Quality Assessment


Transportable Array Sensor Comparison



This is a comparison of the 3 sensors used by the Transportable Array TA network stations: Streckeisen STS-2, Guralp CMG-3T and Nanometrics Trillium-240. The mode of the Probability Distribution Function (PDF) of the Power Spectral Density is used to characterize the most common level of background noise for each of these sensors in-situ. To combine the by-station mode calculations into groups by sensor the mean of the modes is calculated.

PDF data used in this study ranged between September 2004 and October 2008. Each type of sensor is used in various locations across the Array and there is no known bias in terms of site construction or installation.

The plots below illustrate that the majority of the TA sites, regardless of sensor, operate at moderately low noise levels. In general there are not significant differences between sensor types. The Streckein STS-2's and Guralp CGM-3Ts are very similar in both vertical and horizontal character with an exception at long periods where, from about 35 seconds and longer, the CMG-3Ts have a consistently higher noise level than either the STS-2s or Trillium-240s by an average of 4 db. This possbility indicates a higher self noise level at these periods in the CMG-3T than the other two sensors. The Nanometrics Trillium-240s are consistently at lower or equal noise levels compared to the other sensors with the exception of long periods, starting at 70 db, for the horizontal components.

Mean PDF mode by sensor for vertical channels (Peterson new high and low noise models are in gray):

Mean PDF mode by sensor for horizontal channels, (Peterson new high and low noise models are in gray):

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