Implications of dedicated seismometer measurements on Newtonian-noise cancellation for Advanced LIGO

TL;DR

This study assesses how dedicated seismometer measurements can improve Newtonian-noise cancellation in Advanced LIGO, showing that a small number of sensors can effectively reduce low-frequency seismic noise affecting gravitational-wave detection.

Contribution

The paper demonstrates that a limited number of seismometers or tiltmeters can effectively cancel Newtonian noise in LIGO, based on detailed seismic field characterization and correlation analysis.

Findings

Seismometer arrays can effectively predict Newtonian-noise cancellation levels.

A small number of sensors suffices due to high spatial correlation of seismic surface displacement.

Ground tilt coupling observed is consistent with gravitational coupling effects.

Abstract

Newtonian gravitational noise from seismic fields will become a limiting noise source at low frequency for second-generation, gravitational-wave detectors. It is planned to use seismic sensors surrounding the detectors' test masses to coherently subtract Newtonian noise using Wiener filters derived from the correlations between the sensors and detector data. In this work, we use data from a seismometer array deployed at the corner station of the LIGO Hanford detector combined with a tiltmeter for a detailed characterization of the seismic field and to predict achievable Newtonian-noise subtraction levels. As was shown previously, cancellation of the tiltmeter signal using seismometer data serves as the best available proxy of Newtonian-noise cancellation. According to our results, a relatively small number of seismometers is likely sufficient to perform the noise cancellation due to an almost ideal two-point spatial correlation of seismic surface displacement at the corner station, or alternatively, a tiltmeter deployed under each of the two test masses of the corner station at Hanford will be able to efficiently cancel Newtonian noise. Furthermore, we show that the ground tilt to differential arm-length coupling observed during LIGO's second science run is consistent with gravitational coupling.