>Suppose for a bit of cleverness, the lidar designers use a pulsed
>laser and detect synchronously with the pulses. If they used a
>pseudorandom time-sequence of pulses, the jammer-designer would have
>to overpower the high peak power of the pulsed laser and match the
>time-sequence of the pulses to within nanoseconds. Would you really
>want to spend on the order of $50K for a jammer to avoid paying of
>order $1K in tickets?????

I don’t think so Jon – watching some police work with the units – it is
very easy to get an error READING mainly due to an error in it’s
checking algorithm.  - I belive that all you have to do is to put out
noise on the same frequency and it’s error checking will sut it down!

>In article <Bvps0r….@watserv1.uwaterloo.ca> t…@kingcong.UWaterloo.ca (Prateek Dwivedi) writes:
>}Another thought re: laser detectors.  Are they only working on deflection
>}from atmosphere particles?  Or does it work on the laser hitting the car
>}itself.  The latter would be too late, wouldn’t it?

>Yes, it would be too late.  The hope is that the cop guns somebody in
>front of you, and you pick up some of that signal as it’s bouncing around.

Suppose for a bit of cleverness, the lidar designers use a pulsed
laser and detect synchronously with the pulses. If they used a
pseudorandom time-sequence of pulses, the jammer-designer would have
to overpower the high peak power of the pulsed laser and match the
time-sequence of the pulses to within nanoseconds. Would you really
want to spend on the order of $50K for a jammer to avoid paying of
order $1K in tickets?????

—Jon
—

Disclaimer — The government probably disagrees with my opinions.

>}Another thought re: laser detectors.  Are they only working on deflection
>}from atmosphere particles?  Or does it work on the laser hitting the car
>}itself.  The latter would be too late, wouldn’t it?

>Yes, it would be too late.  The hope is that the cop guns somebody in
>front of you, and you pick up some of that signal as it’s bouncing around.

I was in Wal-Mart yesterday and noticed they had a BEL Laser Detector
for around $100.  It claimed up to a 5 mile range.
Is this one of them that was recently tested in a car magazine
article?

Has anyone actually tried one yet?

Russ (rlat…@decster.uta.edu)

Probably the same way any spotlight works.  Remember the car is not
a perfect mirror, some light is scattered in all directions.  This
misunderstanding is probably the result of the sloppy way we use
words in normal conversation (and the news media).  In scientific
terms the laser beam is scattered and part of it returns to the
unit.

>I’m interested in knowing if the laser doesn’t work on different types of
>paint jobs.

>If laser works on reflecting light…. then if I have a "buff" black car
>that absorbs most light…would I be stealth.

Only if all your chrome, your headlights, your license plates, your
reflectors (e.g. turn signals, fog lights, etc.) are ALL painted dull
black as well. If your car if flat balck, but you have a nice shiny
license plate, a LIDAR gun will still be able to get a reading from your
car.

>Another thought re: laser detectors.  Are they only working on deflection
>from atmosphere particles?  Or does it work on the laser hitting the car
>itself.  The latter would be too late, wouldn’t it?

You’re absolutely right. There is no "scatter" from a LIDAR gun, and its
beam is very narrow. When your LIDAR detector goes off, it’s because the
LIDAR beam is hitting YOUR CAR. It doesn’t bounce off of other vehicles,
trees, the road, signposts, or any of the other things that RADAR will.
This is why Car & Driver judged LIDAR detectors to be worthless in their
report on LIDAR.

>Ever since I heard about the laser speed-measuring unit, I have wondered how
>it worked.  As described on our local evening news, the police shine a
>single laser beam onto the car, and it reflects back to the unit [?]
>How is that?  Surely most/all surfaces of the car are not angled such
>as to give reflection straight back to the unit, and I would imagine
>that the laser is a fairly narrow beam.  So, how does it work?

        From what I’ve read, the unit sends out a sequence of pulses and times
each individual return.  However, because the spread in responses would be very
large compared to the accuracy required to deduce the speed from two readings
(e.g. compare the return time difference between one pulse that hits the
cage^H^H^H^Hcar’s headlights and one that reflects from the windshield, with
the accuracy needed to determine a vehicle’s speed to 1 mph in 60 for two
pulses say 1/50 sec apart), the timed returns have to fit to a straight line
within a certain accuracy over a certain period before the unit declares a
valid velocity reading.  Given this, I’m sure you can think of several passive
and active ways to bamboozle the unit — it’s not instantaneous.  A valid
return would be at very low intensity since, as you noted, a true specular
reflection is very unlikely, so car-mounted jammers have a good chance of
over-riding returns (though you can also think of ways the lidar manufacturer
can minimise this…).

>Just curious …
>[my Plymouth Horizon can scarcely go fast enough to speed,
>so I have no need to jam the gizmo]

>John
>sny…@henry.ece.cmu.edu

Ivan Reid, Paul Scherrer Institute, CH.                         i…@cvax.psi.ch
GSX600F, RG250WD.       SI=2.66     "You Porsche. Me pass!"   DoD #484

The laser is low power but as best I can tell, the unit uses interferometry
which provides a high degree of discrimination to other sources of light.
Plus the gun has what looks like a dichroic bandpass filter on the
receiver.  More selectivity.

Note that at a retail price of more than $5000, the technology does not
have to be cheap and does not seem to be.

>(4) Therefore a jamming device does not need to be exactly the same
>frequency as the laser source – it just needs to return enough energy
>in the entire frequency range in which the detector is sensitive to
>overwhelm it. (Note that this can be countered with a frequency
>specific filter on the detector).

You need to realize what you’re saying.  The range of frequencies of light
that falls within the nominal range of IR is massive, comprising many
octaves.  A radio analogy would be to attempt to jam a highly selective
VHF receiver using a wideband noise source that covers from AM broadcast
to microwave.  Even with massive total power from the jammer, the power
concentrated in the band of interest is minimal.  You simply will have
to know more about the IR used in order to jam.  Once you DO know something
about it, generating the necessary power is easy.

>     John, when you get your hands on a lidar gun, a lot of us will be
>interested in what you find. For a start:

I have already had my hands on one for a few minutes.  Because of the
source, no more details regarding the incident are available.

>*     What warnings vs, say, pointing it at the sun, does it carry?

No markings on the gun.

>*     What happens when you point it at a very HOT car – say a black paint
>      job that’s been sitting in the Georgia sun all day?

Probably nothing, as noted above.

>*     If we can’t do a brute force intensity jam, how about an intense,
>      rapidly flickering IR source (eg, hot object behind fan blades)?

My guess is an array of laser diodes shining through a suitable diffuser
would be the most effective jammer.  Given the low price of laser diodes
these days, this would be very inexpensive to construct.

>*     How well does a license plate cover reduce IR return? Glass?
>      Plastic? Should we rely on absorption or reflection away from
>      the lidar? What can we do about rear (and front) reflectors?

This is light. You can easily test your hypothesis by simply shining a
light on your car and observing the reflection.  The LIDAR is not as
sensitive as your eyes so filter your view appropriately.

I spent my time with the gun doing what cops would do – shooting at cars.
My experience was quite similar to _Car & Driver_ in that it is a difficult
unit to operate and requires steady aim.  I only had about 5 minutes with
it so I have only first impressions.  I believe a good defence will be to
minimize the reflective surfaces on the car and to use a detector.  Though
the gun can acquire a reading in under a second under ideal conditions,
under real world conditions it will require several seconds.  I’d not
be surprised to hear someone has developed a clearcoat with IR absorbance
properties.  The market is certainly pregnant.

John
—
John De Armond, WD4OQC               |Interested in high performance mobility?  
Performance Engineering Magazine (TM) |
Marietta, Ga                         |Interested in high tech and computers?
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- Hide quoted text — Show quoted text -

>c…@aoa.aoa.utc.com (Carl Witthoft) writes:

>>x
>>The concept is simple: direct a IR beam at the LIDAR detector which
>>is of sufficient amplitude to swamp the "desired" signal, and which
>>is of appropriate frequency (measured at the receiver, so don’t forget
>>your vehicle’s motion) to read either <speed limit or a random
>>failure.
>>The bigger problem is in aiming your jammer at the LIDAR and doing so
>>fast enough to avoid all true readings.  A continous, wide-angle
>>beam will dothis.  
>>The remaining physics is relatively straightforward and doesn’t differ
>>much from the radar equation used to build a radar jammer.

>Actually the physics are fundimentally different.  The LIDAR (the Laser
>Atlanta unit at least) works by making a sequence of timed distance
>measurements and computes speed from delta distance/delta time.  It does
>NOT use doppler in any manner.  

>I would imagine it would take a fairly powerful and pretty close to
>(optical) frequency to jam the unit.  Doable but not trivial.  I’ll
>know more in a couple of months when I get one in for evaluation.

>John

>–
>John De Armond, WD4OQC               |Interested in high performance mobility?  
>Performance Engineering Magazine (TM) |
>Marietta, Ga                         |Interested in high tech and computers?
>j…@dixie.com                        |Write me about PE Magazine
>Need Usenet public Access in Atlanta?  Write Me for info on Dixie.com.

Ever since I heard about the laser speed-measuring unit, I have wondered how
it worked.  As described on our local evening news, the police shine a
single laser beam onto the car, and it reflects back to the unit [?]
How is that?  Surely most/all surfaces of the car are not angled such
as to give reflection straight back to the unit, and I would imagine
that the laser is a fairly narrow beam.  So, how does it work?

Just curious …
[my Plymouth Horizon can scarcely go fast enough to speed,
so I have no need to jam the gizmo]

John
sny…@henry.ece.cmu.edu

:
: (3) The receiver is probably as inexpensive as possible, and relies
: more on time domain intensity variations to identify it’s returned
: signal than on precise frequency discrimination.

I would presume that the lidar broadcaster sends out sequence pulses with
very particular shapes, and uses some sort of lock-in receiver or matched
filter to search for only that particular pulse shape, and ignore
all others.  That may make it hard to jam.

:                                                       Peter Trei      
:                                                       pt…@mitre.org
:                                                       N1MNV
:

–
-Matt Kennel            m…@inls1.ucsd.edu
-Institute for Nonlinear Science, University of California, San Diego
-*** AD: Archive for nonlinear dynamics papers & programs: FTP to
-***     lyapunov.ucsd.edu, username "anonymous".

No.  They’ll aim for your headlights, bumper, license plate…

}Another thought re: laser detectors.  Are they only working on deflection
}from atmosphere particles?  Or does it work on the laser hitting the car
}itself.  The latter would be too late, wouldn’t it?

Yes, it would be too late.  The hope is that the cop guns somebody in
front of you, and you pick up some of that signal as it’s bouncing around.

Jeff
—
Jeffrey S. Curtis sidewin…@uiuc.edu | "Resplendent and full again, they revel
 The Power of 37  free2207 at uiucvmd | in their role as self-appointed critics
"To be great is to be misunderstood." | of the establishment…"
"Insist on yourself – never imitate." |   — INXS _Welcome to Wherever You Are_