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Example: Correlations in data from the 40m interferometer

The output below was produced starting with 2621440 samples from the 19 November 1994 run 3 data set, covering about 266 seconds.

The fast channels, including the IFO_DMRO channel, were decimated so that all channels are effectively sampled at the slow channel rate of $986.842\dots\,$Hz. This yields a (real) time series with 262144 samples and correspondingly a (complex) FFT of length 131072 as specified by the macro name LENGTH. Averaging is carried out over 128 frequency bins but this may be varied to include a range of bandwidths MIN_BANDWIDTH and MAX_BANDWIDTH.

Figure: The graphical display of the contents of the output file 40m_fft/rho2_IFO_128.dat produced by env_corr illustrating strong environmental cross-correlation. The three graphs show the correlation between the IFO_DMRO channel and each individual environmental channel. This graph is produced by the file corr_view128 which env_corr produces.
\begin{figure}\index{colorpage}
\begin{center}
\epsfig{file=Figures/xmgr.eps,angle=270,width=5in}\par\end{center}\end{figure}

The output was obtained from the commands

corr_init 40m.config

followed by

env_corr 40m.config

where 40m.config is the configuration file printed above. This corresponding to seeking correlations between the interferometer output (IFO_DMRO) channel and

IFO_Mike: The microphone output.
IFO_Seis_1: The seismometer output.
IFO_SPZT: The slow pzt.

The data below show sections of the output file 40m_fft/rho2_IFO_128.dat illustrating strong environmental cross-correlation at around $40$Hz with the seismometer and microphone output, at around $120$Hz with all three channels, and in a broad band around 360Hz with the slow pzt.

... 
39.271          0.000           0.000 0.000 0.000 
39.753          0.654           0.256 0.644 0.000 
40.235          0.000           0.000 0.000 0.000 
40.717          0.000           0.000 0.000 0.000 
41.199          0.794           0.794 0.000 0.000 
41.681          0.000           0.000 0.000 0.000 
...
118.778         0.000           0.000 0.000 0.000 
119.259         0.000           0.000 0.000 0.000 
119.741         0.940           0.528 0.876 0.519 
120.223         0.973           0.371 0.911 0.830 
120.705         0.000           0.000 0.000 0.000 
121.187         0.000           0.000 0.000 0.000 
...
352.478         0.886           0.000 0.000 0.886 
352.960         0.897           0.000 0.000 0.897 
353.442         0.899           0.000 0.000 0.899 
353.924         0.904           0.000 0.000 0.904 
354.405         0.898           0.000 0.000 0.898 
354.887         0.897           0.000 0.000 0.897 
355.369         0.869           0.000 0.000 0.869 
355.851         0.878           0.000 0.000 0.878 
356.333         0.893           0.000 0.000 0.893 
356.815         0.893           0.000 0.000 0.893 
357.297         0.843           0.000 0.000 0.843 
357.778         0.845           0.000 0.000 0.845 
...

Figure: The spectrum of the IFO_DMRO channel before (black) and after `cleaning' based on the three environmental channels discussed in the text using a correlation width of 128 bins (red).
\begin{figure}\index{colorpage}
\begin{center}
\epsfig{file=Figures/cleaned.eps,angle=270,width=5in}\end{center}\end{figure}

The output file 40m_fft/fftclean_IFO_128.dat contains the Fourier transform of the corresponding signal `cleaned' by estimating the transfer functions over a correlation width of 128 bins. Figure [*] shows the spectrum of the IFO_DMRO channel before and after `cleaning' based on environmental channels 1, 2 and 5.


next up previous contents
Next: Example: corr_init Up: GRASP Routines: Signal-to-noise enhancement Previous: Function chan_clean()   Contents
Bruce Allen 2000-11-19