Ring Laser Gyroscope

The Ring Laser Gyroscope is a type of gyroscope that is based on laser beams which move around a cavity. The principle of operation of a RLG is based on the Sagnac Effect, which was famed for showing that light changes velocity on a rotating platform. The changing velocity of light as seen in the RLG and Sagnac Experiments is said to be contrary to the consistency of light as proposed by Special Relativity (See the Michelson-Morley Experiment and Sagnac Experiment).

In the Ring Laser Gyroscope two counter-propagating laser beams are shown to have different frequencies with the difference dependent on rotation rate. Measurements of this difference provides the rotation angle or rotation rate about the RLG's sensitive axis.

The Earth Line
Strapdown Inertial Navigation Technology By David Titterton, John L. Weston, John Weston

From Chapter 15.6 on p.497

p.498

Background Noise
From http://microglacoste.com/gPhoneNoise/gPhoneSeismicNoise.pdf we read:

Airborne Transmission
https://amp.livescience.com/24209-earthquakes-infrasound.html

https://en.wikipedia.org/wiki/Seismic_wave