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Excess power trigger generator. Patrick Brady and Saikat Ray-Majumder University of Wisconsin-Milwaukee LIGO Scientific Collaboration. Excess power method: the basic idea. The basic idea: Pick a start time, a duration (dt), and a frequency band (df)

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excess power trigger generator

Excess power trigger generator

Patrick Brady and Saikat Ray-Majumder

University of Wisconsin-Milwaukee

LIGO Scientific Collaboration

excess power method the basic idea
Excess power method:the basic idea
  • The basic idea:
    • Pick a start time, a duration (dt), and a frequency band (df)
    • Fourier transform detector data with specified start time and duration
    • Sum the power in the frequency band
    • Calculate probability of obtaining the summed power from Gaussian noise using a c2 distribution with (2 x dt x df) degrees of freedom
    • If the probability is small, record a trigger
    • Repeat procedure for all start times, frequency bands and durations
  • For Gaussian noise, the method is optimal to detect bursts of specified duration and frequency bandwidh
    • Details are in Anderson, Brady, Creighton and Flanagan [PRD 63, 042003. (2001)]

GWDAW - Dec 2003

excess power method time frequency decomposition
Excess-power method:time-frequency decomposition
  • Using N data points corresponding to maximum duration of signal to be detected
  • Construct time-frequency planes at multiple resolutions
  • Each plane is constructed to have pixels of unit time-frequency volume
  • Time resolution improves by factor of 2 from plane to plane

GWDAW - Dec 2003

excess power method implementation
Excess-power method:Implementation
  • Calculate time-frequency planes as described above’
  • Compute power in tiles defined by a start-time, duration, low-frequency, frequency band
  • Output is sngl_burst trigger if probability of obtaining power from Gaussian noise is less than user supplied threshold

GWDAW - Dec 2003

tuning the search code
Tuning the search code
  • Parameters available for tuning
    • Lowest frequency to search
    • Maximum and minimum time duration of signals
    • Maximum bandwidth
    • Confidence threshold
    • Number of events recorded for each 1 second of data
  • Tuning procedure
    • Lowest frequency decided based on high glitch rate below 130 Hz
    • Max duration is 1 second; Min duration is 1/64 seconds
    • Max bandwidth of a tile 64Hz, but allows for broader band signals by clustering
    • Tuned confidence threshold and number of events recorded to allow trigger rate ~ 1 Hz

GWDAW - Dec 2003

running the search on large data sets
Running the search on large data sets
  • Excess power runs standalone using Condor batch scheduler
    • Directed Acyclic Graph describes workflow
  • Use LALdataFind to locate data
    • Interrogation of replica catalog maintained by LDR (S. Koranda)
  • All search code in
    • LAL and LALApps (many contributors)
  • Power code
    • Generates triggers from each interferometer
  • Coincidence stage of the search is part of the jobs we run
    • Coincidence needs to be tuned within burst group (See talk by Cadonati)

GWDAW - Dec 2003

performance on interferometer data
Performance on interferometer data

600s: uncalibrated data

Same data with Sine-Gaussians at 250Hz, h0 = 6e-20

GWDAW - Dec 2003

frequency dependence of triggers

800 Triggers

800 Triggers

Frequency Dependence of Triggers

Hanford 4km: # of triggers in various freq. bands

Livingston 4km: # of triggers in various freq. bands



GWDAW - Dec 2003

measuring the efficiency of algorithm
Measuring the efficiency of algorithm
  • Sine Gaussian waveform
    • h+(t) = h0 Sin[ 2 p f0 (t-t0) ] exp[ - (t – t0)2/t2 ]
    • hx(t) = 0
  • Signal parameters used:
    • Frequencies: 235, 319, 434, 590, 801
    • Q = sqrt(2) p f0t = 8.89
    • h0 = [10-21,10-17] uniform on log scale
  • Location on sky for single detector tests:
    • Zenith of each detector
    • Linearly polarized w.r.t. that detector
    • That is F+=1, Fx=0

GWDAW - Dec 2003

parameter accuracy peak time and central frequency
Parameter accuracy: peak time and central frequency

Q=9 Sine-Gaussian at 235Hz

Peak time

Central frequency

GWDAW - Dec 2003

continuing work as part of lsc burst analysis group
Continuing work as part of LSC burst analysis group
  • Tune the coincidence step to best utilize triggers from excess power
  • Extend efficiency measurements to all sky for sine-Gaussians
  • Extend efficiency measurements to include supernova waveforms
  • Implement multi-detector extension of excess power discussed in Anderson, Brady, Creighton and Flanagan [PRD 63, 042003. (2001)]
  • Test alternative statistic involving over-whitened data [See ABCF and/or Vicere PRD 66, 062002. (2002)]

GWDAW - Dec 2003