Quote:
|
Originally Posted by Sally
Lately I've been hearing a bit about posting a speed limit on Winnipesaukee. I'm sure many would agree and many others would disagree about this regulation, but my question is regarding speed enforcement. Does radar work on water? I thought that in order to get an accurate speed rating, the radar had to be on a flat surface, or at least on something steady. Not sure if those MP boats would qualify as "steady."  Maybe someone out there is a little more knowledgeable on this subject and could help me out...  Thanks! |
The radar units would work about the same as they do on land. Due to their relatively wide beam they would be less prone to errors due to rocking and rolling of the MP boat. Conceivably you might find some error sources due to the more reflective nature of water vs land but practically speaking this isn't a big isssue. A bigger issue would be discriminating 1 boat from others and proving you nabbed the right person.
Lidar would be more prone to missing the target as the boat rolls about due to it's much smaller beam (think lidar/spotlight vs radar/floodlight) and would take more effort on the part of the officer to keep on target, but if done properly then the discrimination issue above is moot. Fog of course would reduce effective distances greatly.
Both devices only measure speed directly towards (or away from) the gun (closing/opening velocity). A boat (or car) travelling a speed S, moving at some angle relative to the gun will have a measured speed, M, reduced by the cosine of the angle (M = S x cosine{angle}, cosine{angle} < 1). This is always less than the true speed so you get a break in this regard. Just like on the roadway, the MP would have to pick it's spots to be effective. Time to add a power socket for the detector ?
ps - Military radars, which can track both relative velocity and position , would give true speed (no cosine error). I don't think the commercial radars in use are accurate enough for this to work though.