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Ring Laser Gyroscope

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Revision as of 03:37, 19 February 2019 by Tom Bishop (talk | contribs)

The Ring Laser Gyroscope is a gyroscope that is based on laser beams which bounce 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, and which is said to be contrary to the consistency of light as proposed by Special Relativity, which was derived in response to experiments such as the Michelson-Morley 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

  “ The Fourier transform of the output from the laser cavity gives a spectral line associated with the rotation of the Earth often termed 'the Earth line'. Analysis of this spectral line is used to monitor the impact of seismic waves and other events. This ability to make high-precision measurements of rotation rates has led to applications in geodesy. ”

p.498

  “ The effect of seismic events is to induce frequency-modulated side bands, in the 0.2-1 Hz region, around the 'Earth line', which indicate the presence of rotational components associated with seismic events. ”

Seismic Wave Propagation

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

  “ As earthquake waves ripple through the Earth, the crust buckles, rumbles and roars — both audibly and at infrasonic frequencies, below the range of human hearing. A new study finds the Earth's surface acts like a speaker for low-frequency vibrations, transmitting an earthquake's infrasonic tumult into the air. ”

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

  “ Primary waves (P-waves) are compressional waves that are longitudinal in nature. P waves are pressure waves that travel faster than other waves through the earth to arrive at seismograph stations first, hence the name "Primary". These waves can travel through any type of material, including fluids, and can travel nearly 1.7 times faster than the S waves. In air, they take the form of sound waves, hence they travel at the speed of sound. Typical speeds are 330 m/s in air, 1450 m/s in water and about 5000 m/s in granite. ”

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

  “ It is interesting to speculate on the precise origin of the background seismic noise. Haubrich et al ii for example, open their article with the following description of the seismic noise background and the large interest it has generated over the years as well as the intractability of its investigation:

The low‐level background unrest of the earth, called microseisms or earth noise, has puzzled seismologists and other scientists for nearly a century. The problem of its nature and causes has proved particularly unyielding, not, however, for lack of investigation. A bibliography covering work up to 1955 [Gutenberg and Andrews, 1956] iii lists over 600 articles on the subject; one covering the years from 1955 to 1964 [Hjortenberg, 1967] iv lists 566. Unfortunately, much of this work has advanced the subject but slightly. ”