Towards windproofing LIGO: Reducing the effect of wind-driven floor tilt\n by using rotation sensors in active seismic isolation

Modern gravitational-wave observatories require robust low-frequency active\nseismic isolation in order to keep the interferometer at its ideal operating\nconditions. Seismometers are used to measure both the motion of the ground and\nisolated platform. These devices are susceptible to contamination from ground\ntilt at frequencies below 0.1 Hz, particularly arising from wind-pressure\nacting on building walls. Consequently, during LIGO's first observing run both\nobservatories suffered significant downtime when wind-speeds were above 7 m/s.\nWe describe the use of ground rotation sensors at the LIGO Hanford Observatory\nto correct nearby ground seismometers to produce tilt-free ground translation\nsignals. The use of these signals for sensor correction control improved\nlow-frequency seismic isolation and allowed the observatory to operate under\nwind speeds as high as $15-20$ m/s.\n