StochMon is a DMT monitor which estimates the strength of a stochastic background which could be detected with a false alarm rate of 5% and a false dismissal rate of 5% using one stride's worth of data from a pair of interferometers. By using online data to estimate the stochastic sensitivity, StochMon can provide quick feedback to the operators on the performance of the interferometer.
To obtain its data-quality measurement, StochMon relies on the fact that a pair of interferometers with one-sided noise power spectra P1(f) and P2(f) observing for a time T is sensitive to a stochastic background of strength ΩGW where
ΩGW-2 ∝ T ∫ df [&gamma(f)]2/[P1(f) P2(f)]
Because ΩGW-2 grows linearly with time, we use this as our figure of merit. But, the ΩGW figure of demerit is also available, if preferred.
&gamma(f) is the overlap reduction function, which is equal to unity for colocated coäligned interferometers and has a known functional form for other pairs of detectors. Its form for LLO and LHO is shown below:
StochMon evaluates the stochastic sensitivity by computing the AS_Q-strain transfer function (the ``calibration'' or ``response'' function) and applying it to AS_Q data to estimate the strain noise power spectrum P1(f) of the gravitational-wave channel. The second power spectrum P2(f) is currently read from a file. Future enhancements to the monitor should include calculating this on the fly (for H1-H2 sensitivity measurements) or obtaining it over the network from the other site.
StochMon then reports the following:
The principle forms of output are:
- the current stochastic sensitivity estimate;
- the current amplitude of the calibration line (used to track the interferometer's response function);
- the current values of the calibration parameters `alpha' and `beta' (see the calibration section below).
- a summary web page and shorter `revolver' page available through the CDS homepage;
- the DMTViewer;
- trend files.
StochMon is managed by the Process Manager, and so it should always be running at the sites. If it is missing, please contact John Whelan or John Zweizig.
The standard way to start StochMon isStochMon -config <file_name>where <file_name> is a configuration file. Up-to-date configuration files are usually available on the dmt machines (sand, delaronde, etc) as ~ops/pars/StochMon_H1H2.conf, etc. A sample configuration file for H1 with H2 as the reference is-OSCfile LockLoss.conf -xmlfile ReferenceCalibration_H1.xml -refpsd H2_CalPSD_GPS_793481321.txt -fmin 30.0 -trend H1 H2The last two entry in the configuration file must be chosen among H1, H2, or L1. The remaining arguments (which may be invoked in any order) are listed below. Arguments in red are required.
-fmax # Specify maximum frequency to include in stochastic sensitivity estimate. Default 1400Hz. -fmin # Specify minimum frequency to include in stochastic sensitivity estimate. Default 20Hz. -PSD_DumpPeriod Number of strides between each dump of a calibrated AS_Q PSD. Default 1 (dump every stride). (Use 0 if you don't want any periodic stochastic sensitivity and calibrated PSD dumps) -h, --help Print usage information, then exit. -local Run in local mode. All output files are dumped in the local directory instead of to the default directory specified by the environment variable $DMTHTMLOUT. The plain-text log file is renamed <GPS_Start_Time>.log. -logfile <name> Name plain-text version of log file <name>. Only works if -local option is also selected. Default filename is <GPS_start_time>.log (-local mode) or <IFO>_StochMon_CumLog.txt (otherwise). -max # Specify maximum number of strides to process before program exits. -n # Specify number of sections to divide data into for calculating the noise power spectrum. The 'stride' variable must be a multiple of this number. Default 15. -OSCfile <file> Specify the Operating State Condition configuration file defining the conditions for the interferometer to be in lock; see the `Operating State Condition (OSC)' section below. If not specified, StochMon will attempt to open $STOCHMON_OSCCONF/StochMon_LockLoss.conf, then ./StochMon_LockLoss.conf. StochMon will exit if no OSC configuration file can be found. -refpsd <file> Specify file to be used as reference spectrum for P2(f). -xmlcal Use dynamical calibration based on a reference calibration file . -screen Update and error messages are sent to the screen instead of to the default files <IFO>_StochMon_Log.txt and <IFO>_StochMon_Errors.txt. -stride # Specify length in seconds of data to use for each stochastic sensitivity estimate. Default 60. -trend Write stochastic sensitivity and calibration data to trend files as minute trends. When writing trends it is recommended that `stride' be a factor of 60 (eg: 15, 30, 60). -window <type> Specify data window type for power spectrum estimation, where <type> is one of: `hanning' for Hanning window, `blackman' for Blackman window, `flattop' for FlatTop window (NOT RECOMMENDED), `hamming' for Hamming window (NOT RECOMMENDED), `square' for no window (NOT RECOMMENDED). Default Hanning.
StochMon OutputStochMon produces the following output after every <stride> seconds of data is analyzed if PSD_DumpPeriod is not 0:
Graphical: DMTViewer PlotsThis is the main output of the monitor; the estimated stochastic sensitivity for each stride is exported to the DMTViewer, along with data related to the calibration.
What the channels mean:(Assume the monitor running is StochMon_H1H2) The following series are reported to the DMTViewer (the name of the corresponding channel in the trend files is in parentheses):
- `Stochastic Sensitivity Omega' (H1:DMT-STCH_H1H2_OMEGA) and `Stochastic Sensitivity 1/Omega^2' (H1:DMT-STCH_H1H2_INV_OMEGA_SQ)
These channels report the average stochastic sensitivity which could be detected with a false alarm rate of 5% and a false dismissal rate of 5% using one stride's worth of data from a pair of interferometers. Omega is a figure of demerit and 1/Omega^2 is the figure of merit.
- `Calibration Line Amplitude (ASQ counts)' (H1:DMT-STCH_H1H2_CAL_LINE_AMP)
The amplitude of the calibration line as seen in the AS_Q channel (this is the ordinary amplitude, which is sqrt(2) times the rms amplitude).
- `Alpha' (H1:DMT-STCH_H1H2_CAV_FAC)
The value of the calibration parameter alpha. This quantity is computed using the measured calibration-line amplitudes in the AS_Q and excitation (injection) channels, beta as measured from the DARM channels, and the user-supplied open-loop gain, sensing function, reference line amplitudes, and reference DARM value.
- `Beta From Input Matrix' (H1:DMT-STCH_H1H2_OLOOP_FAC)
The value of the calibration parameter beta as computed from the DARM channels and the user-supplied reference DARM value. The trend channel H1:DMT-STCH_H1H2_OLOOP_FAC contains the product alpha*beta.
Interpreting Plots:StochMon reports zero or negative values for all of these channels under special conditions.
- All Values = 0: The interferometer is not in lock. (StochMon requires that both the both_arms_locked_strict and both_arms_locked_common_mode operating state conditions be satisfied for it to calculate a stochastic sensitivity. These conditions are defined in the file /export/home/ops/pars/LockLoss.conf on sand and delaronde.)
- All Values = -1 or -2: StochMon was not running or had no data for the period in question. When started, StochMon looks for a file containing the DMTViewer histories from the previous run of the program. If no such file is found, StochMon initializes its plots with '-1's. Otherwise, StochMon intializes its plots using the old data and places a '-2' in the latest data spot as a tag to indicate that the preceeding data was read from a file.
- Trends = -1: If no calibration line is tracked (a non-standard configuration) StochMon reports -1 in the trends for the gain, line amplitude, alpha, and beta.
- Alpha = 1: The alpha parameter is calculated from the calibration line, which sometimes is not available. If the computed alpha is not real and positive (which may happen if the calibration line dies) then alpha is reset to unity.
Html and data filesThe following files are by default written to the directory specified by the environment variable $DMTHTMLOUT (set to point to a subdirectory of $GDS_APACHE/monitor_reports/ on sand and delaronde). If this environment variable is not set or if the -local option is used, these files are placed in the local directory instead.
- Web Pages: The files index.html and <IFO>_StochMon_Summary.revolver.html contain summary information, including the stochastic sensitivity estimates averaged over the last 1, 5, and 15 strides. The page index.html also has links to files containing more detailed update information and error messages, unless the '-screen' option is invoked, in which case these messages are sent directly to the user's screen.
- 2-Week Summary: The file <IFO>_StochMon_summary.txt contains a two-week summary of the (gain-adjusted) stochastic sensitivity averaged over 1000-second intervals.
- Calibrated Noise Power: If the IFO is locked, the current calibrated (strain) noise power spectrum is written to the ASCII file <IFO>_CalPSD_GPS:xxxxxxxxx.txt (eg, L1_CalPSD_GPS:715580020.txt) in increments specified by PSD_DumpPeriod in the configuration file. The latest plots are available from the homepage of the current run.
- Trends: Every hour a trend file is produced showing the minute trends for each of the quantities sent to the DMTViewer. These are available at the sites through LDAS.
CalibrationStochMon estimates the strain noise spectrum from the AS_Q data following the calibration notes of Gonzalez et al (2002, 2003). All actual calibration calculations are performed by the FDEasyCalibrate class, which requires as input a specially formatted file containing reference calibration information. These reference calibration files will be produced by the calibration team. The only point that might interest the casual user is that this calibration data should be linearly sampled over a frequency range larger than [fmin,fmax] Hz (see -fmin, -fmax options) and not including 0 Hz or 4096 Hz. StochMon will exit if the calibration data does not cover [fmin,fmax] Hz.
Operating State Condition (OSC)StochMon requires a file stating the conditions which define the 'both_arms_locked_strict' and 'both_arms_locked_common_mode' states for the interferometer. It is recommended to use D. Chin's LockLoss.conf file in /export/home/ops/pars/, which contains up-to-date definitions of these states; in this case one should start StochMon in that directory. The user may alternately specify a precise location and file name at launch. Otherwise, StochMon will search for the file StochMon_LockLoss.conf, first in the directory specified by $STOCHMON_OSCCONF and then in the local directory. You can (re-)set the environment variable STOCHMON_OSCCONF using a command likesetenv STOCHMON_OSCCONF directory_path
Comments, queries, and suggestions regarding any aspect of StochMon are welcome; please email the authors.
Authors: Marc J. Cenac John T. Whelan Version: last modified Jul 12 2005.