Optical scattering¶
The gwdetchar.scattering module provides a suite of tools designed to look for evidence of optical scattering in the LIGO detectors. This tool finds the velocity of a set of optics as measured by optical position sensors and electromagnetic drivers (OSEMs), then compares against the wavelength of a carrier laser to estimate the fringe frequency. For more information about this method, please see Accadia et al. (2010).
The gwdetchar.scattering module provides the following functions:
|
Predict scattering fringe frequency from the derivative of a timeseries |
Note
OSEMs directly measure only the translational (linear) motion of optics, typically on the scale of microns. To measure velocity, gwdetchar.scattering uses a Savitzky-Golay filter to take smoothed time derivatives.
The gwdetchar.scattering.plot module also provides functions for comparing fringe frequency projections against high-resolution Q-transform spectrograms:
|
Compare a high-resolution spectrogram with projected fringe frequencies |
|
Overlay scattering fringe projections on top of a high-resolution spectrogram |
Command-line utilities¶
GWDetChar provides two command-line utilities for optical scattering; one is designed to identify time periods when scattering is likely, the other compares projected fringe frequencies against a high-resolution spectrogram of gravitational-wave strain.
Note
These utilities require authentication with LIGO.ORG credentials for archived frame data access.
gwdetchar.scattering¶
The gwdetchar.scattering command-line interface searches over a standard list of OSEM measurements within a user-specified time range for evidence of optical scattering. The simplest usage is as follows:
python -m gwdetchar.scattering -i `<interferometer>` `<gps-start-time>` `<gps-end-time>`
For example,
python -m gwdetchar.scattering -i H1 1126259442 1126259502
For a full explanation of the available command-line arguments and options, you can run
$ python -m gwdetchar.scattering --help
usage: python -m gwdetchar.scattering [-h] [-V] -i IFO [-a FLAG] [-z FMIN]
[-t FREQUENCY_THRESHOLD] [-x {1,2,3,4}]
[-m OPTIC] [-p SEGMENT_PADDING]
[-s SEGMENT_START_PAD]
[-e SEGMENT_END_PAD] [-L BANDPASS_FLOW]
[-H BANDPASS_FHIGH] [-S SIGMA]
[-c MAIN_CHANNEL] [-f FRAMETYPE]
[-o OUTPUT_DIR] [-w NSCAN] [-v]
[-j NPROC]
gpsstart gpsend
Search for evidence of beam scattering based on optic velocity
This tool identifies broad time segments over which evidence for scattering is
strong. To compare projected fringes against spectrogram measurements for a
specific, narrow time range, please use the `simple` command-line module:
python -m gwdetchar.scattering.simple --help
positional arguments:
gpsstart GPS start time or datetime of analysis
gpsend GPS end time or datetime of analysis
options:
-h, --help show this help message and exit
-V, --version show program's version number and exit
-i IFO, --ifo IFO IFO prefix for this analysis, default: None
-a FLAG, --state-flag FLAG
restrict search to times when FLAG was active
-z FMIN, --fmin FMIN minimum frequency (Hz) of triggers, default: 10.0
-t FREQUENCY_THRESHOLD, --frequency-threshold FREQUENCY_THRESHOLD
critical fringe frequency threshold (Hz), default:
15.0
-x {1,2,3,4}, --multiplier-for-threshold {1,2,3,4}
fringe frequency multiplier to use when applying
--frequency-threshold, default: 4
-m OPTIC, --optic OPTIC
optic to search for scattering signal, can be given
multiple times, default: ['BS', 'ETMX', 'ETMY', 'IM1',
'IM2', 'IM3', 'IM4', 'ITMX', 'ITMY', 'MC1', 'MC2',
'MC3', 'OM1', 'OM2', 'OM3', 'OMC', 'PR2', 'PR3',
'PRM', 'RM1', 'RM2', 'ZM1', 'ZM2', 'OPO', 'OFI',
'SR2', 'SR3', 'SRM', 'TMSX', 'TMSY']
-p SEGMENT_PADDING, --segment-padding SEGMENT_PADDING
time with which to pad scattering segments on either
side, default: 0.05
-s SEGMENT_START_PAD, --segment-start-pad SEGMENT_START_PAD
amount of time to remove from the start of each
analysis segment
-e SEGMENT_END_PAD, --segment-end-pad SEGMENT_END_PAD
amount of time to remove from the end of each analysis
segment
-L BANDPASS_FLOW, --bandpass-flow BANDPASS_FLOW
lower-limit (Hz) of the passband for whitened BLRMS,
default: 4.0
-H BANDPASS_FHIGH, --bandpass-fhigh BANDPASS_FHIGH
upper-limit (Hz) of the passband for whitened BLRMS,
default: 10.0
-S SIGMA, --sigma SIGMA
significance threshold on whitened BLRMS, default: 2
-c MAIN_CHANNEL, --main-channel MAIN_CHANNEL
name of main (h(t)) channel, default: {IFO}:GDS-
CALIB_STRAIN
-f FRAMETYPE, --frametype FRAMETYPE
the frame type name
-o OUTPUT_DIR, --output-dir OUTPUT_DIR
output directory for analysis, default: .
-w NSCAN, --omega-scans NSCAN
generate a workflow of Omega scans for active
scattering, this will launch automatically to condor,
default: 0 (no Omega scans)
-v, --verbose log verbose output, default: False
-j NPROC, --nproc NPROC
the number of processes to use when reading data,
default: 8
gwdetchar.scattering.simple¶
The gwdetchar.scattering.simple can also be run as a command-line module to compare fringe frequency projections against gravitational-wave strain at a specific time. The simplest usage is similar to gwdetchar.scattering, but with only a single time:
python -m gwdetchar.scattering.simple -i `<interferometer>` `<gps-time>`
For a full explanation of the available command-line arguments and options, you can run
$ python -m gwdetchar.scattering.simple --help
usage: python -m gwdetchar.scattering.simple [-h] [-V] -i IFO [-d DURATION]
[-t FREQUENCY_THRESHOLD]
[-m MULTIPLIERS]
[-x MULTIPLIER_FOR_THRESHOLD]
[-w PRIMARY_CHANNEL]
[-W PRIMARY_FRAMETYPE]
[-a AUX_FRAMETYPE]
[-o OUTPUT_DIR] [-c COLORMAP]
gpstime
Simple command-line interface to gwdetchar.scattering
Given a specific GPS time of interest, this module scans through records of
optic motion and projects fringe frequencies due to optical scattering. For
those channels with fringes above a user-specified threshold, a plot is
created comparing the fringes to a high-resolution Q-scan spectrogram.
To identify broader time segments when scattering is likely in the first
place, please use the main command-line module:
python -m gwdetchar.scattering --help
positional arguments:
gpstime GPS time or datestring to analyze
options:
-h, --help show this help message and exit
-V, --version show program's version number and exit
-i IFO, --ifo IFO IFO prefix for this analysis, default: None
-d DURATION, --duration DURATION
Duration (seconds) of analysis, default: 60
-t FREQUENCY_THRESHOLD, --frequency-threshold FREQUENCY_THRESHOLD
critical fringe frequency threshold (Hz), default: 15
-m MULTIPLIERS, --multipliers MULTIPLIERS
harmonic numbers to plot projected motion for, should
be given as a comma-separated list of numbers,
default: 1,2,4,8
-x MULTIPLIER_FOR_THRESHOLD, --multiplier-for-threshold MULTIPLIER_FOR_THRESHOLD
frequency multiplier to use when applying --frequency-
threshold, default: 4
-w PRIMARY_CHANNEL, --primary-channel PRIMARY_CHANNEL
name of primary channel (without IFO prefix), default:
GDS-CALIB_STRAIN
-W PRIMARY_FRAMETYPE, --primary-frametype PRIMARY_FRAMETYPE
frametype from which to read primary channel, default:
{IFO}_HOFT_C00
-a AUX_FRAMETYPE, --aux-frametype AUX_FRAMETYPE
frametype from which to read auxiliary channels,
default: {IFO}_R
-o OUTPUT_DIR, --output-dir OUTPUT_DIR
Output directory for analysis, default: .
-c COLORMAP, --colormap COLORMAP
name of colormap to use, default: viridis