john banks

I am talking about the laser roadside camera vans that read you from afar (no flash), forward facing, people in fog were seeing it only 50 yards or so in front then panic braking even though they were not speeding. Causing chaos!

[Edited by john banks - 11/7/2003 9:44:35 AM]

john banks

Just wondered... presumably they have to be able to see your numberplate clearly and not have too much laser scatter?

What about in the dark or heavy rain?

Not that I would drive fast in the fog or bad conditions, still have a clean license thankfully.

Gridlock Mikey

Good point that man! I suppose that they have some sort of motion sensor or beam that gets broken and then rely on the flash to "illuminate" the crime scene. If it's illegible, they bin it, if it's legible then unlucky.

I should imagine as far as fog is concerned, it would have to be really thick not to be able to see 10ft infront of you. If it were that thick, i wouldn't even get into my car let alone drive it

Heavy Rain, well i suppose there is an argument regarding light getting reflected and distorting the image. Maybe? Dunno

Hope you are keeping well

Mikey

Goochie

In really thick fog I reckon it'd be unclear - think of how your headlights reflect back at you, I guess the flash would do the same.

Rain isnt a problem for them though.

Fatman

No, I don't think the laser scameras would have much chance in foggy/misty conditions. They use infrared lasers, and IR is strongly absorbed by water. That 'damping' effect would be even more effective when the water is finely distributed as in fog/mist.

Goochie

Ahhhh... sorry I misread the original post.

A colleague of mine was "caught" in one of these, she decided to turn round and appologise to the guy in the van to try and get off. Turns out that they cant afford to equip all the vans with cameras at once and this one diddnt have one!

Trouble is that they all look the same from the outside - its just the digital/laser stuff they're lacking.

That was in Lapworth just outside Warwick by the way.

Dracoro

If the fog is too thick for the cameras to read your plate then there's no way you'd be able to go very fast unless you are incredibly stupid & you'd have crashed long before anyway

SirFozzalot

do people really speed in thick fog??

Fatman

I think that APCO guidelines discourage attempted use of laser scameras in such conditions. I'm sure a question on 5ive-0 could direct us towards those guidelines (if they exist).

John: Why, have you recently witnessed exactly this?

Scooby96

"she decided to turn round and appologise to the guy in the van to try and get off"

apologise in what way

pugoetru

Boost II

iTrader: (1)

Thinking logically - why would they be there if they didn't think they would be able to catch anyone - especially if not the most pleasant of days for loafing about.

+Doc+

There should be no way they would catch you as you should be well under the speed limit in fog.

FLAT ERIC

iTrader: (1)

Hmm. So never mind all these expensive lazer diffuser garage door opener (allegedly) thingys.

All you need is a bonnet mounted mister spray bar plumbed in to your headlight washers & you are in stealth mode.

john banks

The fog was very patchy but quite dense nonetheless, maybe they could work intermittently?

Even though they were not apparently speeding, when the camera van pops out the fog on go all the brake lights. I saw this this morning.

IWatkins

Eye safe IR laser has a fairly bad scatter in suspended water droplets (i.e. fog). Even so, in 200m visibility fog (uniform through range) and otherwise standard ICAO atmosphere, a laser at 200m is only going to get back 25.3% of emitted light assuming a perfect reflection.

The question would be what signal return strength do they need to get a reading ?

In addition, once they have a good return can the camera (that I assume uses visible light) see the number plate clearly enough to get a good image ? I calculate that the amount of light reaching a standard photopic range camera will only be 4% in those conditions. Is that enough to get a good image ?

Cheers

Ian

Leslie

Television cameras can definitely produce a better picture in fog than the eye can distinguish. I don't know why or whether a speed camera can do the same though.

Les

Fatman

...because TV cameras are recording visible light whereas handheld s/cameras use infrared light. Different frequencies of light respond to water droplets in different ways (e.g. absorption, diffraction etc).

Ray_li

The speed cameras that the company I work for, do work in fog. As for the laser I dont think they will work but our cameras dont just only work by lasers they also work sensers in the road.

Fatman

Here's a link to a PDF file of the ACPO website. On p66 of the current Code of practice for operational use of enforcement equipment they note that "Heavy rain, spray or mist may reduce the range of the laser but will noteffect the speed measurement".