Noise Projections and their use in GEO 600

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Noise Projections and their use in GEO 600

• Joshua Smith LPF DA Meeting
• 18.07.06

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Noise projections
noise channel
transfer function
detector output
noise source
detector output
noise projections
noise budget
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Simplified procedure

• Notes
• Causality key
• Simultaneous DFTs allow comparison
• Other variants exist, eg open-loop which requires
  CLTF

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Limitations

• Assumes linearity, ie that N(f1) produces H(f1)
• Including nonlinear effects requires model, or
  more sophisticated measurement of TF.
• Loop gain sets limit on use for in-loop signals
• Workarounds exist
• Transfer functions have to be relatively stable
  or measured often

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Software used

• Frame data from GEO is served using self-written
  server (M.Hewitson)
• Matlab client to communicate with server, get
  data (M.Hewitson)
• Noise projection scripts Matlab
• All computations done with standard Matlab
  functions
• Averaged DFTs, fft()
• Averaged transfer functions, tfestimate()
• Averaged Spectra, pwelch()
• Normalizations (PSD, ASD, etc) from Gerhards DFT
  paper

• Plotting all done with Matlab
• Stadard Linux scripts for output (eg
  publication)
• Print, for EPS
• Epstopdf for PDFs, etc for publication (thesis ?
  )
• Continuously running monitor made in Matlab using
  Guide

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Noise projection alignment FB
? feedback
noise projection
transfer function
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Noise proj modulation phase
Works well for very complicated systems
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Noise budget for S5
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Automation

• Nominal signals and their Fourier transforms
  should be available continuously
• Need accurate transfer functions
• Measure once per day/week/month?
• Track continuously at set frequencies?

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Calibration lines
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Tracking transfer functions

• At calibration line, projection and H should have
  same amplitude, phase.
• Ratio and difference indicate TF accuracy.
• For 10 day test, about 10 10o

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Vetoes of false GWs

• Vetoes crucial for burst search
• Noise channels contain almost no GW info
• Coincident (within windows) events are not GWs !

Example injected burst-like waveform
Further research and application continues within
AEI Hannover
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Noise subtraction
Results of a time-domain subtraction
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The End