Title: Noise floor of horizontal ringlaser gyroscopes as derived from atmosphere induced ground tilts.

Abstract:

Next generation gravitational wave detectors will need improved tilt compensation of the suspension of the end mirrors. Ringlasers gyroscopes are one promising technique to detect the relevant geometric tilts since they are insensitive to gravity.

To make inferences about background levels of rotational ground motions we exploit the fact that ground tilts are not only sensed by suitably oriented gyroscopes, but also by horizontal component accelerometers through tilt coupled gravity. Since atmospheric acoustic gravity waves propagate too slowly to efficiently excite Rayleigh waves in the Earth, we attribute horizontal seismic accelerations which are coherent with ambient barometric pressure to tilt coupled gravity. Based on this line of reasoning we can estimate lower bounds of background tilt and background rotation rate for all stations of the Global Seismic Network (GSN).

We find that below 20mHz the barometric pressure induced background rotation rate is 30dB higher than earlier estimates which were based on the assumption that the rotational noise floor is defined by Rayleigh wave motion.