LSC Detector Characterization Working Group
Performance Characterization
Performance characterization, as opposed to transient analysis, centers
on quantifying steady-state behavior of the interferometers. The characterization
includes quantifying the strength of known instrumental and environmental
noise sources, the degree of correlation among important channels, and
the instrument's sensitivity to gravitational radiation sources.
The characterization may be limited to description, or it may be extended
to explicit correction of the data stream for known effects.
Examples of noise sources to be quantified:
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Electrical line contamination (60 Hz & harmonics)
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Seismic noise
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Stack vibration
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Violin modes
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Internal mirror resonances
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Total non-Gaussian noise level
Examples of instrumental behavior description:
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Operational state (e.g., good lock, marginal lock, unlocked)
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Cross-coupling coefficients / transfer functions between dark port and
other channels
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Calibration curve for dark port response
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Optical, rf and geometrical parameters (should be stable)
Examples of astrophysical sensitivity description:
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Strain sensitivity at 150 Hz
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Maximum viewing distance for inspiral standard candle
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Frequency of single-interferometer transients matching astrophysical templates
Examples of analysis tools:
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Statistical description (trends of mean, rms, min/max; band-limited rms,
histograms)
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Power spectra and spectrograms
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Time-frequency plots (waterfall, carpet, wavelet transforms)
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Correlations, autocorrelations
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Matched filters
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Principal value decomposition
Recording characterization results:
The results of performance characterization will be logged routinely
into the meta-database; one important early task of this working group
is to define the nature of that recorded information. Much trend data,
such as channel means and rms's are already planned for recording by the
DAQ system, but deciding how to store more sophisticated measures of performance
requires careful thought and coordination with the LDAS group.
Data correction?
Whether to attempt explicit correction of data for known instrumental
effects is an issue at the interface between the detector characterization
and the other two analysis working groups. Should we subtract known effects
to produce the best estimate of h(t)? Or should we merely identify
and quantify the instrumental effects to avoid introducing additional error
due to imperfect subtraction? Other issues at the detector / astrophysics
interface are techniques to correct for Doppler effects in searches for
periodic sources and to correct for instrumental whitening filters.
General Plan
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Set priorities and find volunteers
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Define structures of meta-database entries (with appropriate flexibility)
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Implement and test simple algorithms to gain experience
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Improve and extend to more sophisticated algorithms