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FightBack Forums _ Technical Discussion of Enforcement Devices _ Type 24 Radar obstructions
Posted by: SpeedDemon666 Thu, 5 Sep 2019 - 14:01
Post #1512864
It is well known that gatso radar devices don't cope well with obstructions, given the multiple stories of stationary vans and large lorries producing return signals. What would this forum make of this situation?
Fixed Type 24 on the roadside, excellent placement with zero roadside obstructions in the field of view except a 30mm chain link fence running along the path parallel with the road.
On the 2 lane road are stationary vehicles queuing near bumper to bumper, they are all normal sized 5/3 door cars the oncoming lane is completely clear. A small two-wheeled vehicle proceeds up the oncoming lane 30 cm from the kerb and passes the camera that is to say the two-wheeled vehicle is "filtering" up the oncoming lane. The camera triggers and registers a high speed.
Is it conceivable that the reading came from the stationary vehicles and not the filtering two-wheeled vehicle
Posted by: bigbadkev Thu, 5 Sep 2019 - 14:06
Post #1512867
anything is possible, but more likley the device triggered on a doppler return from some rotating part of the "small two wheeled" vehicle.
Posted by: The Rookie Thu, 5 Sep 2019 - 14:17
Post #1512871
You seem to misunderstand fundamentally the issue here.
Those cases were NOTHING to do with 'obstructions', they were due to an object in the field of operation vibrating and returning a signal with sufficient Doppler shift to trigger the camera in the way its intended to be triggered by a vehicle exceeding the speed limit.
Could the camera be triggered by a stationary object? Yes
Was it? Well an analysis of the distance travelled by the two wheeler will tell you one way or another, if primary matches secondary the rider would struggle to get an acquittal I'd suggest.
Posted by: bigbadkev Thu, 5 Sep 2019 - 14:38
Post #1512881
being pedantic, there is no way a stationary object can generate a doppler shift, to generate a doppler shift there must be relative movement. If a part of the "stationary" object is vibrating sufficient to generate doppler is must therefore be moving, and hence not stationary...
Turn a pushbike upside down, its stationary. spin its wheels and they may generate sufficient doppler shift to trigger a camera..the wheels are NOT stationary.
Of course you could also knock/vibrate the camera to get the same result but then the camera is the moving object....
and yes i am in that kind of mood today 
Posted by: SpeedDemon666 Thu, 5 Sep 2019 - 16:07
Post #1512917
Interesting thought and given the obtuse angle in this situation could be enough to bring the radar into doubt, which is all I'm looking for
You seem to misunderstand fundamentally the issue here.
Those cases were NOTHING to do with 'obstructions', they were due to an object in the field of operation vibrating and returning a signal with sufficient Doppler shift to trigger the camera in the way its intended to be triggered by a vehicle exceeding the speed limit.
Could the camera be triggered by a stationary object? Yes
Was it? Well an analysis of the distance travelled by the two wheeler will tell you one way or another, if primary matches secondary the rider would struggle to get an acquittal I'd suggest.
Thank you for the correction my assumption was that the radar was being fooled by hearing the return from the opposite side of a large surface like a van but the vibration point still stands, in the case of "two-wheeled vehicles" it is common for the plate to vibrate excessively as the vehicle is going down the road although I can see the mags eyes glazing over on presentation of that argument and would probably require an expert witness to have any hope of swaying the radar into doubt.
As for the secondary evidence the standard measurement lines are obscured by the traffic and my guess(Having yet to see the evidence) would be that only the central dashed lines would be visable, lest plod goes out with a tape measure and pulls some ninja photogrammetry I doubt the secondary will be of much use as unless the distance can be positively proved it's hearsay. In any case given Seroka, R I would expect to see the prosecution thow out the arguments assert the infallibility of the "prescribed device" and rest their case
Turn a pushbike upside down, its stationary. spin its wheels and they may generate sufficient doppler shift to trigger a camera..the wheels are NOT stationary.
Of course you could also knock/vibrate the camera to get the same result but then the camera is the moving object....
and yes i am in that kind of mood today
banging the camera would be a great way of clogging up the system but then again the average british motorist would likley just sign the nip and payout presumung the infalibilty of the gatso in much the same way as the case law forces the courts
Posted by: Jlc Thu, 5 Sep 2019 - 20:14
Post #1512985
We're in the technical discussion part of the forum - This sounds like an actual case?
For photogrammetry they won't be getting a tape measure out...
Posted by: The Rookie Fri, 6 Sep 2019 - 07:26
Post #1513033
If you have both photos its not hard to work out distance travelled.... if that corroborates the radar reading then it was almost certainly correct and no amount of argument about how a radar 'could be wrong' will make one ha'peth of difference.
Posted by: Charlie1010 Fri, 6 Sep 2019 - 07:38
Post #1513035
You definitely need a vibrating object.
We use laser doppler velocimetry to measure the vibrations objects make in engineering applications.
It’s a non interference method compared to the old days of plastering accelerometers all over the place.
Posted by: Sparxy Tue, 10 Sep 2019 - 00:05
Post #1513935
Have you tried calculating the secondary yourself? It may not be 100%, but it may put doubt onto the primary reading. Use anything that's stationary between the two pictures that you know the length of.
Posted by: Sparxy Tue, 10 Sep 2019 - 00:05
Post #1513936
Interesting thought and given the obtuse angle in this situation could be enough to bring the radar into doubt, which is all I'm looking for
You seem to misunderstand fundamentally the issue here.
Those cases were NOTHING to do with 'obstructions', they were due to an object in the field of operation vibrating and returning a signal with sufficient Doppler shift to trigger the camera in the way its intended to be triggered by a vehicle exceeding the speed limit.
Could the camera be triggered by a stationary object? Yes
Was it? Well an analysis of the distance travelled by the two wheeler will tell you one way or another, if primary matches secondary the rider would struggle to get an acquittal I'd suggest.
Thank you for the correction my assumption was that the radar was being fooled by hearing the return from the opposite side of a large surface like a van but the vibration point still stands, in the case of "two-wheeled vehicles" it is common for the plate to vibrate excessively as the vehicle is going down the road although I can see the mags eyes glazing over on presentation of that argument and would probably require an expert witness to have any hope of swaying the radar into doubt.
As for the secondary evidence the standard measurement lines are obscured by the traffic and my guess(Having yet to see the evidence) would be that only the central dashed lines would be visable, lest plod goes out with a tape measure and pulls some ninja photogrammetry I doubt the secondary will be of much use as unless the distance can be positively proved it's hearsay. In any case given Seroka, R I would expect to see the prosecution thow out the arguments assert the infallibility of the "prescribed device" and rest their case
Turn a pushbike upside down, its stationary. spin its wheels and they may generate sufficient doppler shift to trigger a camera..the wheels are NOT stationary.
Of course you could also knock/vibrate the camera to get the same result but then the camera is the moving object....
and yes i am in that kind of mood today
banging the camera would be a great way of clogging up the system but then again the average british motorist would likley just sign the nip and payout presumung the infalibilty of the gatso in much the same way as the case law forces the courts
Have you tried calculating the secondary yourself? It may not be 100%, but it may put doubt onto the primary reading. Use anything that's stationary between the two pictures that you know the length of.
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