New radar detection method?

[thestaton]

Ok, so I was eating lunch with my friend today who was telling me all about his friend who is a cop in Maine and has been apart of the testing method for a new type of speed detection.

According to him it can only be used at night time and it judges your speed by the officer aiming it at your headlight. Seriously I pulled out t the BS flag immediatly however if there was any place that would have the answer I knew it would be here.

Is he full of it or what?

Thanks

Staton

[SmaartAasSaabr]

LIDAR?

[thestaton]

well that is what I asked is it LIDAR and he said no this is new and totally undetectable. because it gets the reading from the acutal light not the reflection sorry I should of clarified.

thanks

staton

[SmaartAasSaabr]

?

How is it possible for it to do that, considering the light is a beam... ie it is travelling at let's say the speed of light ( or c)... so 299 792 458 m / s.

So this unit is precise enough to calculate a difference of a few km/h when the light moves at 1 079 252 849km/h??! :roll: (that's a billion 79 million, 252 thousand 849 kilometres per hour...)

[lordhamster]

?

How is it possible for it to do that, considering the light is a beam... ie it is travelling at let's say the speed of light ( or c)... so 299 792 458 m / s.

So this unit is precise enough to calculate a difference of a few km/h when the light moves at 1 079 252 849km/h??! :roll: (that's a billion 79 million, 252 thousand 849 kilometres per hour...)

Light always travels at the speed of light. If you measure the speed of light C. If you measure light coming from a car heading towards you, its speed will still be C not C + 55mph. HOWEVER.. the wavelength of the light changes depending if the light source is approaching you or going away from you and at what rate. This phenomenon is called the doppler effect, or redshift and blueshift. This is how scientists know the universe is expanding rather than contracting. Imagine staning on a street while a car is approaching you.. When he is approaching you the engine sound sounds higher pitched... as he passes and then goes away from you, the engine sounds changes and becomes lower pitch. Same thing happens with light. Measuring this type of doppler shift is how radar guns work. They shoot a radar signal at you, then wait for the return and measure it's doppler shift.

Theoretically if you have a good enough instrument, you might be able to use this "shift" method to passively (without sending out a signal) determine relative speed, but I don't think it would be accurate enough... since not all headlights will be exactly the same. Radar guns work since the exact frequency and wavelength of the outgoing signal are known and thus you can compare the return.


Current laser speed detection works by firing a laser beam (light) at you. Then measuring how long it takes to reflect back. Since light always travels at the speed of light C, they can calculate how far you are from the gun at the time they shot. They do this distance measurement a second time and they'll know how fast you covered a given distance.. your speed.



Other than the redshift method... the only other method I can think that may work would be to measure the apparant distance between headlights... as a car approaches, its headlights appear to be closer together... the closer it comes the further they get from one another... but again not all headlights are equidistant.

So I'm not sure what he is talking about, but the shifting measurement sounds the most promising... this is essentially how Radar works today, by measuring so called doppler shift.

[SmaartAasSaabr]

You're right. Nothing can exceed c. I must be drunk.

[Ghost]

I think your friend was just talking about LIDAR, and perhaps heard a few of the facts somewhat skewed.

Though the idea of clocking a car based on the blueshift is intriguing, it's also not really feasible. All headlights would have to be emitting the EXACT same frequency with extremely low variation, and all would have to have the exact same plastic/glass covering. And... come to think of it, the earth's rotation and orbit around the sun would affect it to, so it would have to base it off the exact date/time, and a 3-dimensional bearing of where you are in relation to the car. So yeah... only in sci-fi, for the foreseeable future. :)

Using distance between headlights would require that you know the distance of the car from you at one point, and then again at another. In which case you might as well use the variance in the two distances (adjusted a bit based on the angle you're taking the observation at) divided by the time between measurements instead of doing hoo-hah with the distance between the lights.

So, yeah... most likely he was thinking about LIDAR unless I'm just not thinking of something.

[crazyVOLVOrob]

thats what we call LIDAR!

[Veil Guy]

Could be VASCAR.

This is used a lot in PA. The trail of the headlight beam is measured between two arbitrary points, selected by the officer and compared to the officers travelling of the same distance.

Speed of Officer (Known) - Distance Traveled (Between Two Selected Points) :
Speed of Driver (Calculated) - Distance Traveled (Between Same Two Selected Points)

Its totally undetectable and totally lethal.

The Veil Guy 8)

[Ghost]

What are some standard distances used for VASCAR measurement?

[JDM8504]

just a quick question, do cops use LIDAR @ night, i was just wondering, because wouldnt that be hard as hell on the eyes....

[crazyVOLVOrob]

just a quick question, do cops use LIDAR @ night, i was just wondering, because wouldnt that be hard as hell on the eyes....yes they do use it at night they just aim in between at the headlights for a second pull the tigger and lock...speed is locked in

our they could aim for the front licences plate

[carlito]

yes laser can be used at night but its most used in the day time
at night time its cool to see the laser beam going to your car when they shoot laser at u.

[crazyVOLVOrob]

yes laser can be used at night but its most used in the day time
at night time its cool to see the laser beam going to your car when they shoot laser at u.if light was emitted from traffic laser you can test out your laser detection with a laser pointer, but that doesn't set off my BEL

[jimbonzzz]

yes laser can be used at night but its most used in the day time
at night time its cool to see the laser beam going to your car when they shoot laser at u.

You're kidding right? At 904nm, it's not visible to the human eye.
Unless you happen to be driving a Caddy or other vehicle w/night vision and possibly see it on that. Even then, I don't think you would see a "beam" unless there was a bunch of fog/smoke etc in the air.

Jim

[sethy]

yes laser can be used at night but its most used in the day time
at night time its cool to see the laser beam going to your car when they shoot laser at u.
um... lol?

[carlito]

no jim i am not kidding. i saw the laser beam comeing form the gun.
i dont remember if it was foggy though it was a very long time ago :D

[SmaartAasSaabr]

Maybe he was aiming a different kind of gun :shock:

[brick]

Isn't there a european gun that uses a lower wavelength? I thought I read that somewhere on the board, or on a site linked from it. Or I could be on crack...

[carlito]

no it was 95% laser trust me not radar. on a radar gun you cant not see the read beam only on laser.

[jimbonzzz]

Maybe he was aiming a different kind of gun :shock:
Or a laser pointer on his keychain :D

[carlito]

i knew you where going to say something smart :lol:

[jimbonzzz]

Here's a thread where talked about seeing a laser beam:
http://www.radardetector.net/LASER-GLASSES-540t.php

Jim

[carlito]

thanks for the link to the thread. well anyway it was a laser gun i saw and yes it had to be foggy or dust or smoke or to tell you the truth i dont know but i saw the red beam inside the gun.

[jimbonzzz]

Yeah I believe that. If you look at a remote control in a dark room you can see the infrared emitter glow...

Jim

[Veil Guy]

Ghost,

Honestly I don't no precisely, but a tenth of a mile (528') sound about right.

Typically you can spot a VASCAR ticket by two things:

1) Speed is generally indicated to the 1/10th of miph (ie; 122.4 mph)
2) Distance timed should be indicated as well as the qualifier.

The Veil Guy 8)

[Ghost]

Hmm, well if the average person's reaction time is about 0.2-0.3 seconds, then that would give a maximum variance of around 0.6 seconds (0.3 seconds hitting one known point, 0.3 seconds hitting the second). Tracking someone who is going 60 mph for 1/10 of a mile would be tracking them for 6 seconds, with a 0.6 second variance. So you could be "clocked" anywhere between 54mph and 67mph. Higher speeds would produce even greater variance. Interesting that they would give the ticket down to the tenths of a mph with that being the case.

Or is VASCAR automated, and I'm totally off-base in assuming that it involves the officer pressing something when you go over one spot, and then pressing again when you go over a second spot?

[Veil Guy]

Ghost,

I believe you are correct, the officer must trip different counter sequences.

The Veil Guy 8)

[greateratlanta]

Could be VASCAR.

This is used a lot in PA. The trail of the headlight beam is measured between two arbitrary points, selected by the officer and compared to the officers travelling of the same distance.

Speed of Officer (Known) - Distance Traveled (Between Two Selected Points) :
Speed of Driver (Calculated) - Distance Traveled (Between Same Two Selected Points)

Its totally undetectable and totally lethal.

The Veil Guy 8)

So are you saying it is only possible to get a VASCAR reading if the car has its headlights on???

[Veil Guy]

Negative,

Lights trails are the preferred tracking method at night.

During the day, generally any two stationary points of reference may be used as the target car (and tracking vehicle) pass by them.

I hate to say it, but I have gotten pulled-over three times in the last four months with this.

The local yahoo's are crazy when it comes to this sort of enforcement in PA (of course, they have little other choices as laser/radar is approved only for use by state troopers.)

The Veil Guy 8)