[time-nuts] Q/noise of Earth as an oscillator
Tom Van Baak
tvb at LeapSecond.com
Fri Jul 29 13:19:33 EDT 2016
Scott Stobbe wrote:
> I believe a phase noise plot deep into the uHz or lower would apply to the
> rotation rate of the earth.
Yup. You'll see lots of uHz to Hz noise plots by people working with seismic noise, for example. My introduction to the subject were the many plots and papers that describe the heroic effort LIGO goes through to measure tidal and seismic noise in order to keep their gravity wave servos locked. Short-term, the surface of the earth is a very noisy place. But if you can model or measure it before it hits the mirrors, you can mostly back it out.
One can use PN and ADEV statistics on earth rotation, just like any other clock or oscillator. And it seems we can also compute Q for the earth, as if it were a mechanical oscillator.
The remaining question in this thread is if earth Q measurement has actual meaning, that is, if the concept of Q is valid for a slowly decaying rotating object, as it is for a slowly decaying simple harmonic oscillator. And that's were get into the history and definition(s) and applicability of Q to non harmonic oscillators, such as coils, capacitors, atomic clocks, planets, pulsars, etc.
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