StochMon: A Stochastic Sensitivity Monitor for the DMT

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:

[plot of overlap reduction fcn]

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:

Running StochMon

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 is

     StochMon -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 H2
The 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

-max #           Specify maximum number of strides to process before program

-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 

-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 Output

StochMon produces the following output after every <stride> seconds of data is analyzed if PSD_DumpPeriod is not 0:

Graphical: DMTViewer Plots

This 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):

Interpreting Plots:

StochMon reports zero or negative values for all of these channels under special conditions.

Html and data files

The 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.


StochMon 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 like
     setenv STOCHMON_OSCCONF  directory_path

Contact Info

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.

Laser Interferometer Gravitational-wave Observatory