From: jgd@dixie.com (John De Armond)
Newsgroups: rec.autos.driving,rec.autos
Subject: Lasar radar again *sigh* (was Re: IRD?...Infra-Red-Detector?)
Date: 16 Apr 92 05:18:25 GMT
Organization: Dixie Communications Public Access.  The Mouth of the South.

jimf@centerline.com (Jim Frost) writes:

I've had a chance to put my hands on the new Kustom LIDAR.  for a few
minutes. Under less than optimum conditions (translate secret).  
Nontheless I learned a lot.  This unit was designed for Kustom
by Lasers Atlanta here in Atlanta.

>- Most chemical lasers are very tunable and there are few FCC
>regulations against tuning them anywhere in the visible and
>near-visible range.  Thus a detector would need to detect coherent
>light in a very wide frequency range, which is difficult to say the
>least.

The laser is not chemical.  it is a moderate power infrared
diode laser and is not tunable.  It operates more or less CW. 
Acquisition time varies from less than a second under lab
conditions to several seconds under more typical situations. 

>- Lasers are highly directional.  If you're in LOS (line-of-sight)
>it's pretty easy to detect laser radiation, but at that point the
>laser wielder already has you (in the Army's terms, if you're being
>radiated there's probably a bomb on the way).  If you're not in LOS
>then you're seeing reflected radiation which will be:

This ain't the army and their ain't no bombs on the way.  And the laser
is no where near as good as the military.  Under lab conditions (translate
LIDAR fixed on a tripod, target stationary) the spot illuminates much of 
the front of the car at tactical ranges.  Under field conditions (translate
pig holding the gun and pointing) the entire car is painted by the beam.
This is easy enough to observe by trying to aim a laser pointer or
other visible laser at some object 500 yards distant.  The beam is slightly
defocused in order to make the unit easier to aim.  All this coupled
with the fact that the unit takes several seconds to acquire lock means
a detector would be most useful and effective.  Other techniques 
would be more effective.

A much more effective countermeasure is simple jamming.  An array of
infrared laser diodes arrayed across the front of the car and equipped
with divergent lens to make the beams spread and overlap will be 
most effective.  Enough power to swamp the poorly protected photo-
diode should be easy enough to come by.  There are no laws regulating
infrared light so there is nothing specifically preventing this
other than the usual crap about interefering with a pig.

>In my opinion it's likely they'll start using laser speed finders, but
>that there won't be many of them around until the cost drops
>significantly.  I don't believe that there's a lot anyone can do about
>it except hope they have a car that isn't very reflective in the
>frequency range in use.  Note that we nicely fixed Steve's car in this
>respect :-).

Actually there is reason for hope that the LIDAR will be thrown out of
court.  It is fairly easy to create false fast indications by 
panning down across the windshield to the front bumper during the 
measurement.   This technique is easy to learn.  The court accepted
radar because there was supposidly no way to make it read false.
Since it can easily be demonstrated that the operator CAN make
the LIDAR lie, all it will take is the proper court case and 
the proper lawyers.  I believe NML is working on that.

Considering that and considering that a $300 radar can generate 
as much revenue with much less operator effort (translate the pig
can sleep until the overspeed alarm wakes him up) and considering
that the LIDAR cannot be used for moving revenue collection,
it will remain, regardless of cost, just a gadget the pigs roll
out when the cameras are rolling as a weapon of intimidation.

In my opinion if you get stopped by a LIDAR you probably deserve it 
because you could not have been paying attention well enough to have
allowed the pig to get a fix on  you.

John
-- 
John De Armond, WD4OQC        | What's the difference between Jane Fonda
Rapid Deployment System, Inc. | and Bill Clinton?  Hanoi Jane went to 
Marietta, Ga                  | Viet Nam.              
jgd@dixie.com                 | Need public access in Atl?  Write me.
Newsgroups: rec.autos.driving