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From: hbb@e4.ius.cs.cmu.edu (Ben Brown)
Subject: Re: WANTED: Electronic compasses and gyros.
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Organization: CMU Vision and Autonomous Systems
References: <DULIMART.93Oct25205508@pacific.cps.msu.edu> <af.2062.33.0NAF5F03@mecheng.fullfeed.com>
Date: Wed, 27 Oct 1993 14:19:24 GMT
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In article <af.2062.33.0NAF5F03@mecheng.fullfeed.com>, greg.jackson@mecheng.fullfeed.com (Greg Jackson) writes:
...

> There are also people that make laser ring gyros which use
> interferometer techniques and relativistic principles to check out
> acceleration.  Those devices work wherever relativity applies (most
> places I can think of) and are pretty accurate.  I think they are core
> devices for aircraft navagation.  The light goes around a circle (hence
> the term "laser ring") in both directions.  When the ring accelerates
> forward, the light on one side of the ring is phase shifted from the
> light that is currently on the other side of the ring.  The phase shift
> is measured from shifts in the interference pattern as the two light
> paths collide. While the shift is pretty small for non-relativistic
> speeds, the light wavelength is smaller still and the system provides
> good sensitivity to acceleration.  A double integral of acceleration
> will yield position but watch out for integrator drift.

Wouldn't this be an angular *velocity* (not acceleration) sensor? (Hope
I'm not exposing my ignorance of relativity!) This would require a single, 
not double, integration to get position.

	Ben
