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#1
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I had always heard that the police can't use radar guns in the rain because it gives an inaccurate reading. Then today I saw a cop parked in the median of the interstate using one in a pretty good downpour. Perhaps I believed a UL all these years? Googling provides answers both ways. This vendor's site has on their FAQ:
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#2
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This is just a quick thought off the top of my head. I do work with radars, however, not the type used by police. But emitted radar energy behaves the same largely independent of the type of radar emitting it.
There are some wavelengths that are horrible in rain, or snow, or sand. Others are fine. In one of our radars, our detection range is reduced by about 12% (range and radar not identified for my own reasons). Everything up to the reduced maximum range is still as accurate as ever. Your observed police officer may very well have reduced range, but unless his maximum range was reduced to mere metres, I would submit that he would still have enough space to get his required readings to issue a ticket. |
#3
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Also, a significant portion of the "radar" guns you see police using these days are actually laser based, not radar based. I don't know if those are affected by rain either, but seeing an officer using a speed measuring gun doesn't automatically mean they are using radar.
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#4
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What's the normal effective range of one of those devices?
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#5
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If the radar gun was visible, like held out a window or something, his main purpose might not be to ticket people but to get them to slow down in dangerous conditions, for fear of getting a ticket. IOW, he could just have been bluffing.
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#6
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in my neighborhood, as you enter the "school zone" there is a large sign that reports your speed back to you a a reminder -- it normally tracks for about 500 meters. in rain, in snow, night or day -- i have not seen a difference -- as soon as i can see it, it can see me --
i am pretty sure its not some super high tech device --- |
#7
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#8
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What UEL said. Different atmospheric conditions will affect different wavelengths. Fog or mist might be the worst because of its density, but that all depends on how "thick" the air is with moisture. FWIW, my radar detector consistently warns me of only laser and Ka band down here in Arizona when near police, though X and K are found in automatic doors in parking lots and the detector reports those faithfully as well. I have no proof, but I strongly suspect that police here only use Ka band (with respect to "radar"). That being the case, I got a warning for speeding on the 4th of July last year, on a rare rainy day. The radar performance was, apparently, not affected enough to matter to the deputy who have me the warning. I did not have my detector that day, and was not watching my speed on the long, straight road into my subdivision (speed limit 45).
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#9
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#10
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My guess is that the policeman simply did not know the limitations of his tool, or simply didn't care. At least, it's common enough here for them to behave like that.
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#11
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The reason weather radar works, is based on the reflection of the water droplets. A droplet reflects the signal, some drops reflect more, all based on the wavelength of the signal.
This varies with type of radar, etc. Higher frequency devices need much smaller drops to get a full reflection. A big drop, oh, say "car-sized" wouldn't be much of a problem even with the rain. fog would be the worst culprit. For you math geeks out there, this might be some help. |
#12
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So I can get away with speeding when visibility is poor and the roads are slick! Awesome! I see no downside to this!
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#13
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Would this apply to speed cameras? Just recently the Baltimore Sun did a big study on how accurate Baltimore City cameras were and the results were not pretty. The company claimed that environmental conditions affected the accuracy and that the cameras worked fine. Naturally the City defended the cameras.
Here is one article about the issue. And another one. |
#14
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LIDAR is affected by rain. It's a light beam. So fog, rain, smoke, etc will shorten the effective distance. It's ironic that people always try to fight speeding ticket based on RADAR by googling things on the internet. Most errors cause by RADAR technology actually show a DECREASE in speed and not an increase in speed. The best way to beat a RADAR ticket is ask for the logs for the RADAR gun. It's common the officer either does not test the unit or does not document the testing of the unit. At least in California it's expected to be done at the start of the shift and at the end of the shift. |
#15
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The logs are not generally available throughout the country nor is the officer likely to have them available at the time the ticket is being issued. The logs can be subpoenaed by your lawyer if needed.
Richard (who is known to drive fast) |
#16
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Comment: I heard that the ornamental "bull balls" that you see people hang
from the back bumper of their trucks (or other model vehicles) can throw off the results of a police radar detector gun or scanner. That can't be true, and if it is, it would have to be a specific brand designed for that purpose, right? |
#17
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The reply to that is contained in the query. Bull!
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#18
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In addition to weather interference, I think you don't see it used in the rain because the device and the officer need to be exposed to the weather. As for accuracy of any of it in rain, I think the first goal is simple intimidation making people think you're getting a reading even if you're not. And I'm cynical enough to believe that many cops would pull someone over and claim they were speeding whether they had a valid reading or not. |
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