review timing and waveform quality:
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II GSN Calibration Procedures November 16, 2011 Peter Davis Project IDA Scripps Institution of Oceanography University of California, San Diego. Review timing and waveform quality:. sample rate correction. Sensor failure:. loss of vacuum. Getting the metadata right …. - PowerPoint PPT PresentationTRANSCRIPT
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Project IDA (International Deployment of Accelerometers)Project IDA
II GSN CalibrationProcedures
November 16, 2011
Peter DavisProject IDA
Scripps Institution of OceanographyUniversity of California, San Diego
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Review timing and waveform quality:
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sample rate correction
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Sensor failure:
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loss of vacuum
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Getting the metadata right…
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Traditional calibration procedures verified the DAS sensitivity and measured shape of system response.
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DC Calibration Test
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Convolve model of sensor response with input
Compare observed output with model
Iterate until fit acceptable
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Random binary test determines shape of response curve within 1%
Step input to digitizer determines sensitivity to > 0.1%
Manufacturer provides value of sensor generator constant to within 1%
What these tests measure:
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Random binary test determines shape of response curve within 1%
Pitfall – capturing the input signal, test only ‘snapshot’
Step input to digitizer determines sensitivity to > 0.1%
Pitfall – compensate for system load
Manufacturer provides value of sensor generator constant to within 1%
Pitfall – not verified
What these tests measure:
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Sumatra-Andaman earthquake excited many low frequency normal modes
Figure from Park et al. (2004), courtesy G. Roult
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Portable sensors used to check sensitivity of permanent sensors:
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Relative performance of GSN as a network Pitfall – no measure of absolute sensitivity Pitfall – accuracy limited by mode coupling Pitfall – need a very large earthquake to excite the
mode to observable amplitude
What this test measures:
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Tides are a continuous, constant signal Tidal amplitudes can be predicted to 1% accuracy
globally Tides are observed at all times at most GSN
stations Pitfall – must include effects of ocean
loading Pitfall – horizontal sensors effected too
strongly by local tilts Pitfall – tidal periods outside band of seismic
interest
Why use tides?
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Accurate determination of relative response of the common instruments
Accurate determination of relative orientation
What comparing co-located broadband sensors measures:
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Select data from common time period:
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Correct for modeled response:
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