Quality Control
Efforts on USArray Data
at the IRIS DMC
The IRIS Data Management Center (DMC) serves as the
final archive for data from USArray, an element of the EarthScope project.
A small group of data control analysts is responsible for the DMC’s QC
of near-real time data from the seismic components of USArray: Transportable
Array (TA), an array of 400+ instruments that is progressively moving
eastward across the United States; Reference Array (RefNet), a permanent
network of 100+ stations; and Flexible Array (FA), instruments available
to researchers for short-term experiments related to EarthScope (the
majority of the FA data is not available in near real-time). As a supplement
to QC performed upstream from the DMC, the goal of these efforts is to
maximize the scientific usefulness of the data by timely identification
of instrument problems, siting or vault issues, and metadata errors,
and by documentation of the station’s history and performance.
After
near real-time seismic data arrives at the DMC, automated quality measurements
are calculated using QUACK (Quality Analysis Toolkit) and PQLX. Some
of these measurements include data coverage, gap and overlap counts,
signal mean and RMS, Power Spectral Densities (PSDs) and Probability
Density Functions (PDFs). The PDF measurements are further utilized in
creating the PDF Mode Timeline and Color Grid (spectrogram) products
which visualize changes in background noise and instrument performance
over time. Other products which are available to analysts but not automated
yet include waveform comparison with seismic event synthetics and tidal
synthetics.
In addition to reviewing the QUACK reports and PDF products,
analysts routinely use PQLX to view TA and RefNet station waveforms,
both unfiltered and filtered, looking for issues that affect station
performance. Specific problems are reported to the relevant network operators
as they arise (or the PASSCAL Instrument Center in the case of FA stations);
weekly reports document the state of the TA and RefNet. Significant issues
that may affect data users are further documented in the form of Data
Problem Reports which are available at http://www.iris.edu/data/dpr.htm.
As new stations come online, analysts create station history text files
that are updated with information concerning station installation and
removal, site visits and repairs, instrument changes, and metadata changes.
This creates a convenient record of significant events for each TA and
RefNet station.
Examples
Waveforms viewed with PQLX
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PDF Mode Color Grid
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PDF Mode Timeline
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PDF
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USArray is a huge undertaking and relies on the efforts
of many institutions including (but not limited to) the DMC, the Array
Network Facility, the Array Operations Facility, the PASSCAL Instrument
Center, the USGS NEIC/ASL, regional network operators, universities,
and state geologic surveys.
More information about USArray QC can be
found at: USArray Quality Control Overview and Resources at the DMC
Submitted by Gillian Sharer and Chad Trabant, IRIS
DMC |
