Example: ifo_clean

0 This example program uses remove_spectral_lines() to automatically identify and remove ``spectral lines" from the output of the 40-meter IFO. To run this program, be sure to set the data path environment variable, for example:
setenv GRASP_DATAPATH /usr/local/GRASP/data/19nov94.3
The program outputs graphs in a two files called ifo_clean_data.out and ifo_clean_spec.out, containing the before/after time series and spectra. These may be viewed with xmgr by typing:
xmgr -nxy ifo_clean_data.out
and
xmgr -nxy ifo_clean_spec.out
to start up the xmgr graphing program.

The output of this program is a list of lines removed:

Total number of lines removed: 39
Removed line frequency 30.717 Hz amplitude 0.78 phase 15.54 (F-test 68.6)
Removed line frequency 79.203 Hz amplitude 0.55 phase -157.41 (F-test 52.5)
Removed line frequency 80.257 Hz amplitude 0.12 phase -101.84 (F-test 39.3)
Removed line frequency 109.318 Hz amplitude 4.52 phase 10.21 (F-test 75.5)
Removed line frequency 120.009 Hz amplitude 0.46 phase 5.01 (F-test 537.9)
Removed line frequency 139.584 Hz amplitude 0.29 phase -163.57 (F-test 304.5)
Removed line frequency 179.938 Hz amplitude 21.91 phase -43.22 (F-test 3635.0)
Removed line frequency 239.867 Hz amplitude 0.45 phase 130.25 (F-test 42.2)
Removed line frequency 245.438 Hz amplitude 0.21 phase -116.94 (F-test 51.9)
Removed line frequency 279.167 Hz amplitude 0.31 phase 0.52 (F-test 47.2)
Removed line frequency 299.947 Hz amplitude 15.37 phase -135.82 (F-test 9712.5)
Removed line frequency 359.876 Hz amplitude 1.17 phase 61.64 (F-test 134.8)
Removed line frequency 419.955 Hz amplitude 4.48 phase -39.58 (F-test 356.1)
Removed line frequency 488.768 Hz amplitude 0.19 phase 165.56 (F-test 50.5)
Removed line frequency 500.212 Hz amplitude 0.64 phase 129.38 (F-test 34.5)
Removed line frequency 539.964 Hz amplitude 5.09 phase 119.38 (F-test 425.2)
Removed line frequency 571.585 Hz amplitude 4.01 phase 120.03 (F-test 50.6)
Removed line frequency 578.662 Hz amplitude 34.97 phase -149.12 (F-test 429.8)
Removed line frequency 582.426 Hz amplitude 107.36 phase 15.64 (F-test 1129.7)
Removed line frequency 597.936 Hz amplitude 58.72 phase 63.27 (F-test 558.6)
Removed line frequency 605.314 Hz amplitude 17.21 phase -140.57 (F-test 489.7)
Removed line frequency 659.822 Hz amplitude 2.20 phase -152.53 (F-test 121.0)
Removed line frequency 779.831 Hz amplitude 3.95 phase -39.18 (F-test 502.4)
Removed line frequency 839.760 Hz amplitude 2.75 phase -172.15 (F-test 468.2)
Removed line frequency 899.840 Hz amplitude 3.40 phase 113.05 (F-test 529.6)
Removed line frequency 959.919 Hz amplitude 0.80 phase 178.70 (F-test 43.2)
Removed line frequency 999.822 Hz amplitude 1.01 phase 67.74 (F-test 114.8)
Removed line frequency 1019.698 Hz amplitude 1.46 phase -156.72 (F-test 146.6)
Removed line frequency 1079.777 Hz amplitude 3.00 phase 51.82 (F-test 128.9)
Removed line frequency 1157.023 Hz amplitude 2.99 phase -76.14 (F-test 129.4)
Removed line frequency 1210.778 Hz amplitude 2.12 phase 128.39 (F-test 69.5)
Removed line frequency 1319.644 Hz amplitude 3.02 phase -105.29 (F-test 146.2)
Removed line frequency 1499.582 Hz amplitude 1.31 phase 141.94 (F-test 50.5)
Removed line frequency 1559.662 Hz amplitude 2.79 phase 107.12 (F-test 60.0)
Removed line frequency 1746.978 Hz amplitude 1.81 phase 50.38 (F-test 112.0)
Removed line frequency 2039.697 Hz amplitude 1.65 phase 165.82 (F-test 62.3)
Removed line frequency 2279.413 Hz amplitude 2.12 phase -25.06 (F-test 163.0)
Removed line frequency 3509.465 Hz amplitude 0.11 phase 43.89 (F-test 60.1)
Removed line frequency 4609.720 Hz amplitude 0.03 phase 24.61 (F-test 39.4)

Virtually all of these lines can be identified as either 60 Hz line harmonics, or as specific suspension and pendulum modes. The removal of these lines makes a dramatic difference to the appearance (and sound of) the signal, as shown in Figure . Note that the amplitudes of the lines above are properly normalized (in ADC units). For example the 180 Hz line harmonic is well described by . By far the largest amplitude lines are the three violin modes at 578.662, 582.426, and 597.936 Hz, and the 180 and 300 Hz line harmonics. Most of the structure visible in Figure  is the result of these five harmonics.

Figure: Output of the example program ifo_clean, making use of remove_spectral_lines() to automatically identify and remove ``spectral line" features from the (whitened) output of the Caltech 40-meter interferometer. The black curve and the red curve show the before/after time series and spectra. We have deliberately choosen a stretch of data immediately after the IFO locks, so that the suspension and pendulum modes are excited.

Includes/ifo_clean.tex