Suppression of tilt-induced low frequency noise at Ligo Livingston Observatory *

A well known fact is that horizontal seismometers are have sensitivity to ground rotation at low frequencies. Conventional tiltmeters and seismometers cannot discern between rotation of the ground and horizontal acceleration. This is especially problematic for seismic isolation in current gravitational wave detectors, such as Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO), where rotation noise poses limits to duty cycle of the detectors. Earthquakes, High Wind and High Microseism cause significant down-time of both detectors. All are primarily related to the problem of tilt-horizontal coupling producing too much ISI motion.

To address this problem we use a rotation-sensor to get a tilt-free ground translation signal and use it for sensor-correction at LIGO Livingston Observatory as well as at Hanford. I will describe the system in general and present our latest improvement of controls and suppression of low-frequency noise using this system. This should give us a substantial increase of duty cycle of the detectors at O3 during tilt-noise dominated periods.