Xref: utzoo rec.autos:15788 sci.electronics:5332 misc.consumers:8922
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!noao!asuvax!anasaz!john
From: john@anasaz.UUCP (John Moore)
Newsgroups: rec.autos,sci.electronics,misc.consumers
Subject: Re: : Laser radar operation
Keywords: radar, laser, lidar?
Message-ID: <1606@anasaz.UUCP>
Date: 23 Feb 89 14:31:17 GMT
References: <8260@netnews.upenn.edu> <3349@stiatl.UUCP>
Reply-To: john@anasaz.UUCP (John Moore)
Organization: Anasazi Inc, Phoenix AZ
Lines: 26

In article <3349@stiatl.UUCP> john@stiatl.UUCP (John DeArmond) writes:
>In article <8260@netnews.upenn.edu> depolo@eniac.seas.upenn.edu.UUCP (Jeff DePolo) writes:
>Not true.  I have seen no specs on the new unit so this is speculation.
>I expect that they will be using interferometry instead of doppler.  A
                                  ^^^^^^^^^^^^^^      ==    ^^^^^^^
>recovered reflection is mixed with a sample of the incident beam and a
>detector is used to count interference edges.  The countrate is convertable
>into speed.  This is how such instruments designed for other applications
>work.  Using interferometry, all the receiving optics need do is recover

This is identical to doppler processing - you are just thinking of it
in the phase domain rather than the frequency domain. To detect
doppler on a radar signal, just mix the outgoing and incoming frequencies.
The audio difference frequency is the doppler. Measuring the
frequency of this difference frequency (=== counting the cycles == interference
edges!) and doing simple math with the carrier frequency gives you the
speed. This is how a police radar works. A simple radar uses a "gunnplexor"
which has a circulator and a mixer diode. The circulator causes some of
the transmitted energy to impinge on the mixer diode. The antenna causes
the reflected signal to also hit the mixer diode. Audio comes off the diode
and is processed for speed.
-- 
John Moore (NJ7E)           mcdphx!anasaz!john asuvax!anasaz!john
(602) 861-7607 (day or eve) 
The opinions expressed here are obviously not mine, so they must be
someone else's. :-)