LIDAR: Lasers Nab Leadfoots
May 1st, 2007 by Chris Bauer
LIDAR (Light-Imaging Detection and Ranging) is the new generation replacement for the older Radar systems that police have been using to catch speeders. LIDAR uses an IR Pulsed Laser Diode to measure speed, distance and direction. By using beam width of less than one-degree, it’s significantly more accurate than the older radar systems. As the beam crosses the traffic lanes, it can also target a single vehicle at a time and minimize the possibility of false readings.
When the LIDAR instrument transmits light out to a target, the transmitted light interacts with and is changed by the target. Some of this light is reflected back to the instrument where it is analyzed in a fraction of a second. The time for the light to travel out to the target and back to the LIDAR device is used to determine the range to the target. LIDAR guns fire multiple pulses of light each time a police officer pulls the trigger. By measuring the difference of the reflected light pulses, LIDAR guns are then able to determine the traveling speed of their target. Watch out all you lead foots!
You may watch the LIDAR: Lasers Nab Leadfoots TV story online.
Video Games for All and Underwater Flight (episode #109), in which LIDAR: Lasers Nab Leadfoots is a short story, airs tonight on QUEST at 7:30pm on KQED 9, and KQED HD, Comcast 709. (full schedule)
Chris Bauer is a Segment Producer for television on QUEST, and is the producer for this story.
Tags: KQED, kqedquest, QUEST, Science
Posts
Speed the main culprit ? The greatest brainwashing propaganda since the invention of wheel !
Unrealistic speed limits do not work toward safety , instead in the long run , people will see those tools ,laser , as a mockery of safety and fast easy money machine .
Loud music , eating ,cell phone , inattention , fatigue, zigzaguing … all factors not taken in the equation …
Who cares for a true road safety ?
While I liked the program, there are many inaccuracies in the piece.
LIDAR divergence (spread) IS similar to radar, just not as wide. One officer is mistaken about THIS fact and mis-spoke.
To have an officer claim its “pin point” (a marketing “claim”) vs radar, means he fully doesn’t understand the concept of a beam that spreads as it gets farther away from the “Stacked” laser Diode array. Then again, LTI never mentions how wide the beam(s) actually are at reference distances either. They mention ~3 milliradians and equate this to 3′ wide @1,000 feet. Most operators are clueless to this fact that 3′ wide isn’t “pin point”.
The dot in the HUD (Heads up display) of the Marksman only shows speed unless the “range” button is QUICKLY toggled back and forth. QUICKLY, I say, because the ~10 year old LIDAR he uses is the same one I have and its info in the HUD is only viewable for 2-3 seconds.
The Marksman really limits the feedback to the operator WRT: the crucial data needed in real time to determine IF the vehicle clocked is actually the vehicle (or surface) aimed at. Just having the speed displayed in the HUD isn’t all the info the operator needs to know to make a positive determination that the info returned, is indeed the targeted vehicle’s speed. The distance should also be shown as it is in a Stalker LIDAR HUD for instance……
The HUD “dot” isn’t representative of the actual beam of the LIDAR beyond ~150 feet. Considering that its also not in line with the Transmitting lens, there is an additional parallelax error introduced between the site aim and the actual Tx lens of the LIDAR.
Next, the LTI comes with a shoulder stock for steady aiming. A requirement in the operators manual. Considering that department spent the extra $1000 for the HUD option, these officers choose NOT to use the stocks to steady their aim, which leads to many operator errors in aiming, like panning an sweeping of the intended targets.
The voice over person incorrectly states how many pulses of reflected / refracted light are made by the gun; for a reading and each second.
Most LTI Marksman LIDAR guns produce 125 pulses per second. The gun CAN calculate speed using less than 1/3 of them in perfect test conditions.
The gun does so roughly in THIS “approximate” way:
A few pulses are sent and hopefully received back.
Of these first few pulses, they are compared to each other to see if the target vehicle / item is moving.
Then the next series of ~40 or more pulses are examined to see if the return values, when applied to a line (by the method of least squares) can calculate a speed. I say calculate (through an algorithm LTI won’t disclose) because all a LIDAR gun can do is measure distances over time…..
Its these 40 or more returns which are used to attempt to calculate a speed. If there are 125 pulses per second, the 1/3 of a second means that
at least 40 plus pulses are needed to obtain a calculated “speed” reading.
LTI claims a reading can be obtained in 1/3 of a second. The MArksman is actually very quick in its target acquisition, but its accuracy lies in the fundamental flaw of simple LIDAR against moving, sloped shapes and the ability of the operator to precisely operate the LIDAR gun accurately.
LTI boasts that each space shuttle uses their LIDAR guns to determine distances in space, but most spacecraft have large, mostly flat surfaces which reflect LIDAR beams back very well. Not quite an apples to apples comparison to vehicle traffic, now is it?
Accurate aim is to induce panning and actually focus on one “point” of a vehicle and pan/move along with that same point the entire time the reading is being calculated. Most *think* they can accomplish this (these officers without using a shoulder stock) but, consider the moving target “in a perfect scenario” moving 60 MPH (88 feet per second) the operator will have to of moved along with THAT point on the vehicle ~29 feet in 1/3 of a second. No small feat.
There are a few other points I’ll think of later on, and for those reading, my descriptions are a ballpark of the operation of the LIDAR gun shown in this TV piece.
Lastly, I can’t believe a 2007 TV show features LIDAR guns from cicra: 1997 either.
-Suf Daddy
Two quick points:
The TV show simulated the HUD info display. It is NOT an actual LTI MArksman HUD display reading.
The “speed” reading value (if selected) blinks for about 2-3 seconds then disappears. IF you select “range” you get distance info only, its one or the other, causing the operator to not have one of the two info bits (Speed & Distance) available during sighting of the target vehicle.
The Officers are shooting cars mid corner (in a curve) opening the entire side of a vehicle to the pan and sweep effects of the LIDAR beam reflecting back to the Rx (Receiving) lens. Usually, when aimed dead ahead, the slope of the hood, windshield and roofline come into play, here the officers choice of location, for surprise, introduces an additional influence which could either add or subtract from the vehicles calculated speed readings determined by the LIDAR gun…..IMHO poor location choice.
Since the LIDAR beam is invisible to the operator and motorists, who knows if the HUD dot is actually properly aimed? Some of the aim calibration test wouldn’t actually pick up a mis aligned instrument if careful consideration wasn’t
given to rule out a HUD dot misalignment……..
-Suf Daddy
Disappointing, Suf Daddy hits the points dead on.
At the end of the day, LIDAR is still more accurate than RADAR. RADAR requires the operator to discern which vehicle is travelling the fastest. LIDAR, with a beam that is only 3 feet wide at 1000 feet distant is much more exact. Sure it may not be a “pin point” but it is much more exact than RADAR.
Further, parts of the LIDAR beam that are reflected by curved surfaces of a car never return to the gun, they get reflected off elsewhere. So, only the pulses that return to the gun are analyzed. That is why LIDAR and RADAR work.
Moreover, police, who are prudent, test their equipment before they use it, every time. Testing the calibration for speed readings is vital to citations holding up in court.
While I admit that “bumper pacing” with a calibrated and certified spedometer is still the most accurate way for police to catch speeders, using devices like LIDAR and RADAR guns help a lot. Especially on narrow city streets with traffic that would hinder attempts to “bumper pace.”
It is safe to say that this blog is simply a gaggle of people who are bitter that they got caught speeding. Sorry guys. As much as you think you can debunk RADAR or LIDAR, you can’t. You should think about slowing down instead.
One last thing, you guys act like you’ve uncovered some super secret conspiracy to use faulty equipment to entrap innocent people. RADAR and LIDAR are not monumental frauds being perpetrated on the American people. Quite on the contrary, they are necessary parts of traffic safety.
Be thankful that you live in California and not other states like Maryland where speed enforcement is done with automated cameras, like red light cameras around here.
At the point you are punished for not operating within the guidlines, why not take free will out of the equation. Install speed limiters on vehicles, no vehice can exceed 65. People will still drive too fast for conditions, but accident impact speeds will partially be reduced. If we were truly concerned with safety this would be a likely outcome.
Speed laws only serve to generate revenue. People will continue to speed as long as they have the ability too. Laws only effect those that choose to abide by them.
Safety would better be served through attention to intentionally distracted drivers. Ticket those that talk on cell phones, put on make up, listen to music too loudly, etc… Speed is not the main culprit, it is just one of many. But, it is an easy act to identify, target and ticket.
You are free to act as you will, but be mindful of the consequences.
I am interested in anyone that has a reputable source of information regarding the faulty nature of the LIDAR (a journal reference or research paper). I recently was victimized by the “Accurate” LIDAR system. I was locked into going 65 MPH in Cruise Control on 680 in a brand new-paper plates still car and was pulled over and told the LIDAR clocked me at a ludicrous 90 MPH (from 1815 feet away)! Being that I was locked into 65 on my cruise control and that I have never driven 90 MPH in my life, I am out to prove that there can be serious, wide ranging error in this method. I am a scientist and would love to present findings on the LIDAR system in a scholarly manner to help myself and others prove the strong window of doubt cast among some LIDAR readings.
I also was ticketed on 680 just north of 580 interchange about 4 miles. I had my cruise set at 68 and with the slight downhill run was possibly doing 71/72. I also have never driven faster than 75 (Arizona) and think something else is causing serious misreads of their lidar. I also noted a vehicle passing me about 30 seconds before I saw the CHP in my rear view mirror, I wonder about target acquisition and mistaken plate reads?
For further info please see http://www.geocities.com/stop_abuse/LTI2020/OpinionE.htm
I had LIDAR touting cop walking 15 to 20 feet while taking speed check.
With that kinda handling,I’m sure the court walls will be closing in at 25MPH (J)
I’ll appeal the lower court decision.
To my educated guess,the cheap looking silver plastic gizmo, which I was shot at might be in donation to cops from insurance company.
It is safe to say, each equipment pays its cost in first two traffic tickets to donor insurance company.