As part of the Eöt-Wash Group, I develop and build low-frequency precision beam balances (BRS) that are used to sense ground rotations for the seismic isolation systems of the LIGO gravitational wave observatories. Our sensors can sense rotations down to ~0.1 nrad and are now deployed at both LIGO observatories at Hanford, Washington and Livingston, Louisiana.
We use these sensors to remove the tilt signal that contaminates the seismometers that are used to sense the motion of the ground beneath the observatories. Seismometers are spring mass systems which makes them susceptible to spurious forces such as the change of the direction of gravity if the seismometer is tilted. If this signal was used in the seismic isolation systems, we’d be injecting motion instead of removing it.
At the observatories, the dominate source of tilt is the wind pushing on the walls which deforms the concrete slab. Before the installation of our rotation sensors, the observatory could not operate in windy weather. After they can operate without independent of wind speeds up to ~15 m/s.
In addition to these ground rotation sensors, we are developing a compact version with interferometric readout to be installed in vacuum on the isolation platforms.
Rotation sensor designs:
Beam Rotation Sensor, 1-m scale ground sensor: https://github.com/mpross/BRS-Schematics
compact Beam Rotation Sensor, 30-cm scale prototype: https://github.com/mpross/cBRS-Schematics
Cylindrical Rotation Sensor, 30-cm scale in-vacuum sensor: https://github.com/mpross/CRS-Schematics
“Precision Mechanical Rotation Sensors for Terrestrial Gravitational Wave Observatories“. M.P. Ross. PhD Dissertation. University of Washington. (2020)
“Towards windproofing LIGO: Reducing the effect of wind-driven floor tilt by using rotation sensors in active seismic isolation,” Michael P Ross, Krishna Venkateswara, Conor Mow-Lowry, Sam Cooper, Jim Warner, Brian Lantz, Jeffrey Kissel, Hugh Radkins, Thomas Shaffer, Richard Mittleman, Arnaud Pele, Jens Gundlach. Classical and Quantum Gravity (2020).
“Observation of a potential future sensitivity limitation from ground motion at LIGO Hanford,” Jan Harms, Edgard Bonilla, Michael Coughlin, Jenne Driggers, Sheila Dwyer, David McManus, Michael Ross, Bram Slagmolen, Krishna Venkateswara. Physical Review D 101, 102002 (2020).
“Implications of Dedicated Seismometer Measurements on Newtonian-Noise Cancellation for Advanced LIGO“, M. W. Coughlin, J. Harms, J. Driggers, D. J. McManus, N. Mukund, M. P. Ross, B. J. J. Slagmolen, and K. Venkateswara. Phys. Rev. Lett. 121, 221104