Tumbleweeds and airborne gravitational noise sources for LIGO

TL;DR

This paper analyzes various airborne and ground-based gravitational noise sources affecting LIGO, finding most are below noise thresholds but transient shocks and tumbleweeds could produce significant false signals requiring mitigation.

Contribution

Revisits and extends previous studies on atmospheric and airborne gravitational noise sources, including transient shocks and moving objects, with new assessments of their impact on LIGO.

Findings

Gravitational noise from atmospheric density perturbations is below advanced LIGO's noise floor.

Transient atmospheric shocks could generate large false signals, detectable by acoustic vetoes.

Wind-borne objects like tumbleweeds could produce significant signals, necessitating physical barriers.

Abstract

Gravitational-wave detectors are sensitive not only to astrophysical gravitational waves, but also to the fluctuating Newtonian gravitational forces of moving masses in the ground and air around the detector. This paper studies the gravitational effects of density perturbations in the atmosphere, and from massive airborne objects near the detector. These effects were previously considered by Saulson; in this paper I revisit these phenomena, considering transient atmospheric shocks, and the effects of sound waves or objects colliding with the ground or buildings around the test masses. I also consider temperature perturbations advected past the detector as a source of gravitational noise. I find that the gravitational noise background is below the expected noise floor even of advanced interferometric detectors, although only by an order of magnitude for temperature perturbations carried along turbulent streamlines. I also find that transient shockwaves in the atmosphere could potentially produce large spurious signals, with signal-to-noise ratios in the hundreds in an advanced interferometric detector. These signals could be vetoed by means of acoustic sensors outside of the buildings. Massive wind-borne objects such as tumbleweeds could also produce gravitational signals with signal-to-noise ratios in the hundreds if they collide with the interferometer buildings, so it may be necessary to build fences preventing such objects from approaching within about 30m of the test masses.