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-   -   Laser distance, angle & operation (https://www.speedtraphunter.net/police-laser-lidar-enforcement/1809-laser-distance-angle-operation.html)

esprit888 2009-09-11 03:03

Laser distance, angle & operation
 
Hi All,
I am trying to find details concerning the optimum distance and operational guidlines for typical (is there such a thing?) police lasers. I recently received an excessive speeding ticket that was way beyond the capabilities of the car. The officer (who was actually a very nice young guy)was sitting in his car, holding the laser in his hand, he stated he had me at a distance of 795 meters, going away from him, and up a very steep hill (with two cars close behind me)
He would have been at least 100feet below me and i am sure his view would have been partially obscured by the other two vehicles. The beam at that distance i believe would have been in excess of 3 meters (10feet?) I am attempting to identify the type of device used but i was told that at that distance the slightest movement of the laser would render inaccurate readings unless the device was on a tripod? Also that typically the police use 500 to 700 feet as an optimum distance for accuracy?
Are there any web based resources to read up on the use, distance, beam width etc?
Many thanks

Veil Guy 2009-09-13 13:14

When you say beyond the capabilities do you mean at a speed greater than the maximum achievable in your vehicle?

Generally cosine angle errors tend to always favor the driver and occur at very close range.

I suppose, though, that given the nature of your description that there may have been sufficient beam divergence--assuming the beam was greater than 8 feet in diameter at nearly 2500 feet away--to have struck one of the other vehicles behind you for a brief period of time and perhaps could have been used in error in inflating what you departing speed was when subsequent readings were taken off of your vehicle.

Perhaps you can mount a successful argument on this front. In my opinion readings taken at that distance with other vehicles in close proximity is a definite no no and likely not in accordance with any proper guideline of laser usage because of beam-divergence errors.

Veil Guy :driver:

Craig 2009-09-13 22:18

795 meters is a fairly long shot but on a departing target, not particularly difficult to make. There's a host of variables that could influence the possibility of incorrect target identification, which is the defense you're proposing. Something produced that target speed; you have a better chance of winning the lottery than proving in court that the laser conjured up the speed all on its own. At least, in 19 years of operating lasers I've never seen it done out on the road.

Before launching into all of these factors, do us both a favor and answer three questions that'll allow me to focus my response and save everyone some time: What target speed did he assign to your vehicle, how close to actual was that speed and was either of the two nearby vehicles traveling at close to that target speed? Without this information, we could waste days with pure conjecture.

Knowing this, I may be able to help you.:)

Craig

esprit888 2009-09-14 19:34

1 Attachment(s)
To clarify:
All speeds and measurements in metric. I was heading up the hill (shown on the picture attached ) and had passed one vehicle on the flat section and another on the rising section before pulling in prior to the passing line terminating (as the officer said, all done correctly with signals etc) He commented to me whilst issuing the ticket that he had me at 80KPH as I was passing the second vehicle and that he ‘gave me' that as I needed to pass safely and get back in prior to the bend. He then stated that I continued to accelerate up the hill before the road curves out of sight, and that he locked on at a speed of 148KPH (the posted speed is 60KPH) When my passenger questioned the officer about the distance the officer retrieved the laser and showed the indicated speed of 148KPH and a distance of 798 meters. I should note that the picture is taken approx half way between the officers hidden car and the 795 meter mark. I am going to take pictures from the officers hiding spot to the 795 meter mark (using a friends laser range finder) and place my car at the exact point along, hopefully, with two other cars behind me to accurately reflect the conditions. The time was 1730 and the sun was very bright at the top of the tree line cresting the hill.

My concerns are, after trying to duplicate the speeds and verifying the performance capabilities of my car, it simply is not possible to accelerate from 80 to 148KPH in the time or distance available before going out of sight. The officer who issued the ticket was the driver of the police car and was hand holding the laser utilizing his other arm as a steadying point. I am looking for answers or pointers to the following:

1.)Is it acceptable/common practice to handhold the laser at distances approaching 800 meters?
2.)Is it possible that slight movement by the officers hand would result in an erroneous reading ? (wide beam divergence)
3.)Would the suns blinding of the laser have any effect?
4.)What is the optimum range officers are trained to operate the laser at?

I will also mention that I am 51 years old and have a clean license, no accidents, no tickets. This section of a new road, which would make a very good F1 track, has become a real cash cow for the police as 99.9% of the tickets issued are for drivers coming down the hill, which requires serious braking all the way to stay within what is generally considered a ridiculously low speed limit. I intend to request a copy of the officers notes for that day and to ascertain how many, if at all, other tickets for 148 were issued. There are other aspects of the ticket that do not meet the legal requirements however I am more concerned with how this speed was ascertained as I know its beyond the cars capabilities in stock form.

Speed Trap Hunter 2009-09-14 23:55

espirit888,

As the site's primary admin, I want to be perfectly clear that Craig is merely a member of the forum community as I hope you will continue to be here. He certainly is not a judge, jury, and executioner despite his particular wit, which I suspect has been in part brought on from having fielded many questions from others claiming that they were improperly cited. So please do not take that as a personal, shot, for it was not.

As the Veil Guy had posted in his initial response, 800 metres is quite a distance to get a reading when others vehicles are in such close proximity to the primary target.

With respect to guidelines for proper police lidar operation. The judge from the state of NJ had ruled that police laser shouldn't be operated at distances greater than 1000 feet (300 metres) because of the potential of picking up reflections from vehicles other than the primary target from the beam divergence that takes place. At nearly 2.5 times that distance in your situation, the potential for beam divergence is obviously greater.

Is this something that could have happened in your case, possibly, perhaps if your particular vehicle has a relatively lower laser cross-section than the other vehicles that were close by.

I wouldn't expect a ruling in the USA would carry any weight legally in your country of origin, but knowing about the ruling and the circumstances that its was intended to mitigate, probably can't hurt you in attempting to mount a successful defense.

As Craig accurately pointed out, lighting conditions will only have an affect on range and won't introduce erroneous readings.

I have been able to get faulty readings with panning errors, but only when extremely close to a non moving target (ie; wall) and I trust had would have no potential contribution to creating an erroneous reading, either.

Cosine errors don't sound applicable here either. Cosine errors tend to always favor the motorist, btw.

With respect to whether or not it is common practice, that would largely depend upon where you are. The highest distance I have heard from someone receiving a citation was a shot taken in California at nearly 1800 feet (545 metres).

I hope this helps you mount a successful challenge.

BTW, any idea the model of the police lidar gun used? Was it indicated on the citation?


STH


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