Median Based Noise Floor Tracker: NoiseFloorMon

The Noise Floor Monitor tracks slow variations or 'drifts' in the noise floor (that component of interferometric data that is left behind after the lines and obvious transients are subtracted).  The algorithm implemented by the Monitor is based on the technique described in the paper Median based noise floor tracker : robust estimation of noise floor drifts in interferometric data. S. Mukherjee, Classical and Quantum Gravity, 20, S925-S936,2003. (download pdf)

Monitor's Output

The output of the monitor is a set of time series representing the running median estimate of the second moment for different frequency bands. These estimates are calculated for different channels. Furthermore, the monitor computes the standard deviation sigma of white noise by a Monte Carlo simulation with a Gaussian distribution N(0,1). Every time an estimated second moment crosses the three sigma threshold, a trigger is recorded and the data is inferred to have departed from the stationary behaviour. The monitor accepts many parameters which have to be specified in a configuration file. Some of these parameters are the size of the time stride, the number and values of the frequency bands and the channels to be processed. Additionaly the monitor produces a 12 hour data trend plot. 

The result files record four quantities : the minimum, maximum, rms of the output and percentage of the data points crossing the threshold in a one hour period. Those segments that record more than 25% threshold crossing need further attention and are useful for construction of data quality flags.

Detector's Lock Condition

The Monitor process the input time series when the detector satisfies the lock condition "*:Both_arms_locked_strict_cm". If this condition is not satisfied, the Monitor will produce a zero time series for each band processed.

How To Run the Monitor The monitor can be run with the following commands :

Recommendation
Due to the fact that the Noise Floor Monitor can process many channels simultaneously, it is recommended to process the two main channels Hanford 1 and Hanford 2 with one Monitor, i.e. these two channels can be specified in one configuration file at Hanford.

Monitor Report

Current Running Status
Error Messages