Scattered light monitoring system at the Virgo interferometer: performance improvement and automation based on O3 data

Scattered light, also referred to as scattering, is a nonlinear non stationary noise that can affect data acquired by ground-based laser interferometers for the detection of gravitational waves. A methodology for the identification and daily monitoring of scattering sources, based on the tvf-EMD algorithm, was applied to a large dataset of 132 days of data. Time series of the differential arm motion (DARM) degree of freedom acquired by the Virgo detector during the third LIGO-Virgo scientific run, so called O3, which lasted from 1 April 2019 to 27 March 2020, were considered. The analysis focused on correlation with suspended West end optical bench (SWEB) position data, as SWEB was a known culprit of scattering witnessed in DARM during O3. Different configurations were tested, improving performances with respect to previously obtained results and at the same time making the methodology fully automated. This allows to employ it as a monitoring system both during the phases of detector's upgrade and in scientific runs such as the fourth scientific run, O4, currently scheduled to start on 2023. The higher values of correlation obtained suggest that tvf-EMD could improve the performance of scattered light noise subtraction from DARM.