Effects of Aging Hardware on Data Quality
Abstract
For over twenty years broadband seismometers have been used for nuclear explosion monitoring at teleseismic distances. Short period seismometers have also been used to improve resolution at higher frequencies (> 1 Hz) over regional distances. At the time of installation, a calibration process is implemented to determine the proper scale factor between digital counts and ground motion for the seismic subsystem (seismometer and digital waveform recorder). This scale factor is called "calib" and is applied at a single period called "calper." Under this framework the instrument response model is stored in a frequency amplitude phase (FAP) format, which normalizes the response to unity at the calper. The two hardware components at a site that are used to construct the calib are the digital waveform recorder (DWR) and the seismometer of interest. The digital waveform recorder has an associated scale factor from counts to volts and the seismometer scale factor between volts and ground motion (valid in the flat portions of the instruments' respective passbands). Under proper calibration, the relative gain between co-located broadband and short period seismometers should be 0 dB across their common passband as defined in their FAP files. Recently, data from eleven stations with co-located broadband and short-period seismometers have been analyzed for their relative gains using a common time window and their most recent calib scale factors. The relative gains vary between 0.4 and 2.0 dB at 1 Hz, which translates into a 4.7% to 26% amplitude scaling difference between the seismometers at 1 Hz. One complicating factor is the calper at 1 Hz for the short-period seismometer. The Sandia National Laboratories (SNL) Facility for Acceptance, Calibration and Testing (FACT) was tasked with assisting our customer in determining the reason for the amplitude scaling differences.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2011
- Accession Number
- ADA569471
Entities
People
- Darren M. Hart
- Kyle R. Jones
Organizations
- Sandia National Laboratories