During the summer of 2010, IRIS, in collaboration with the USGS/GSN, GSN Standing Committee and Networks Operations at ASL and UCSD, embarked on a review of GSN data quality. The primary objectives of this effort was to develop new procedures for waveform quality assessment and accurately openly report data quality issues for each station to the user community.
Reasons for the review include:
- Reports from the Lamont Waveform Quality Control Center (WQC) and studies by ASL and IDA documented a number of significant problems with the long-period response of some of the aging STS-1 seismometers. The WQC reports also documented a number of other problems with completeness and accuracy of metadata for some GSN stations. The 2010 review carefully documented these response and metadata issues and reported them to the user community.
- With the completion of the major installation phase of the GSN, and funding to recapitalize the recording equipment in the network and add secondary broadband sensors where before there were none, it was possible to remotely calibrate all sensors and provide inter-sensor comparisons. Procedures were developed to exploit this enhanced capability to routinely calibrate and report on full instrument response.
- With the increasing similarities between the instrumentation technologies used by the GSN and other IRIS programs, especially the USArray Transportable Array, there was an opportunity to establish “pan-IRIS” metrics and procedures for tracking and reporting on data quality. Representatives from all IRIS programs were involved in the data quality initiative and sought synergies for enhanced quality control and reporting across all programs.
A GSN Quality Assessment Team (QAT) was established, led then by Kent Anderson as GSN Operations Manager, and involving members of the GSN Operations Group, IRIS Data Services and USArray. They prepared a report on Data Quality Assessment to:
- document current waveform quality problems on a station-by-station basis
- review and correct current metadata for all stations, as necessary
- identify sources of waveform quality problems and develop a timetable for correction
- review historical data to document and correct problems with metadata and response information
- develop procedures and metrics for routine quality assessment
- coordinate with other network operators to evaluate best practices
The IRIS Board of Directors appointed an external GSN Data Quality Panel co-chaired by Barbara Romanowicz and Thorne Lay, with Harley Benz, Göran Ekström and Hiroo Kanamori as members, to:
- review existing reports on the status of GSN data quality
- review proposed new data quality metrics, assessment and reporting procedures
- recommend additional actions for improved data quality control and reporting
This Panel met during the summer of 2010 to review documentation produced by the Lamont WQC and the GSN Data Quality Assessment Team and reported back to the IRIS Board in that fall.
The following links describe the various aspects of our initiative and link to supporting documentation for this plan.
It is our intention to keep the GSN dataset of the highest possible quality and to publicly announce known problems with sensors to minimize errant interpretations of anomalous data.