Daily monitoring of scattered light noise due to microseismic variability at the Virgo interferometer

TL;DR

This study analyzes the relationship between microseismic environmental noise and scattered light noise in the Virgo gravitational wave detector, demonstrating a method for real-time monitoring and characterization of scattered light noise sources.

Contribution

The paper introduces an adaptive analysis method, pytvfemd, for characterizing scattered light noise in gravitational wave detectors using nonstationary time series data.

Findings

Correlation between seismic activity and scattered light noise identified.

The methodology effectively characterizes scattered light noise during O3.

Higher seismic noise correlates with increased scattered light glitches.

Abstract

Data acquired by the Virgo interferometer during the second part of the O3 scientific run, referred to as O3b, were analysed with the aim of characterising the onset and time evolution of scattered light noise in connection with the variability of microseismic noise in the environment surrounding the detector. The adaptive algorithm used, called pytvfemd, is suitable for the analysis of time series which are both nonlinear and nonstationary. It allowed to obtain the first oscillatory mode of the differential arm motion degree of freedom of the detector during days affected by scattered light noise. The mode's envelope i.e., its instantaneous amplitude, is then correlated with the motion of the West end bench, a known source of scattered light during O3. The relative velocity between the West end test mass and the West end optical bench is used as a predictor of scattered light noise. Higher values of correlation are obtained in periods of higher seismic noise in the microseismic frequency band. This is also confirmed by the signal-to-noise ratio (SNR) of scattered light glitches from GravitySpy for the January-March 2020 period. Obtained results suggest that the adopted methodology is suited for scattered light noise characterisation and monitoring in gravitational wave interferometers.