From: jreiser@scott.skidmore.edu (Jason Reiser... Asleep)
Subject: Re: CHP can't use radar?(Was: What radar d
Organization: Skidmore College, Saratoga Springs NY
Date: Mon, 21 Dec 1992 09:23:28 GMT

tzs@stein.u.washington.edu (Tim Smith) writes:
> lstowell@pyrnova.pyramid.com (Lon Stowell) writes:
> >    They are also technically ignorant of how small aircraft measure
> >    their own speed...and how difficult it is to pace an auto from
> >    the air.  Also they are ignorant of the difference between air
> >    speed and ground speed...and how impossible it is to measure
> >    ground speed unless you know the exact winds aloft at your
> >    altitude at the specific time of the flight.
> 
> Here's how the cops claim they do it:
> 
> 	They measure how long it takes the aircraft to go between the
> 	markers, while they observe the car.

Here we go again Leo!

> 	From this, they determine the aircraft ground speed (65 MPH in
> 	the case I was reading).
> 
> 	They note that they are going the same speed as the car, hence
> 	the car is speeding.
> 
> The court says (I use the singular rather than the plural, because I could
> only find one California appellate case where someone objected to this on
> the basis of it being a speed trap) that this is NOT a speed trap, because
> the aircraft is using the marker to measure its own speed, rather than
> using them to measure the speed of the car.

Well, I'll give this method credit as being the most outrageous way of
nabbing a speeder that I have heard to date.  Besides the fact that
its primary purpose is to use a loophole in the law, it isn't really a
possibility.  Sure, a plane could time itself between those two
points, but consider each of the following problems... First, you
would have to assume that the plane is able to "pace" the car for some
set and marked distance... not an easy feat at any considerable
altitude; Hell, it's hard enough to do right when behind the target
vehicle.  Next, we are assuming that the plane is travelling in a
directional vector that is equal to that of the car, right?  If the
plane changes altitude, it increases the distance between the two
points on the ground which it is above, thereby altering the
calculated speed.  If the plane wanders at all, the same problem
exists.  Finally, we also have to assume that someone in the plane can
accurately calculate when they are directly one line and then the
other... I don't know how high these guys fly, but I seriously doubt
that is possible!  
	Oh yeah, I almost forgot to add this.  Keep in mind that
planes and boats rarely travel in a direction vector equal to their
destination.  If there is a wind coming from the left to right side of
the plane, it is effectively travelling a longer distance to stay on
course (above the road in the case mentioned) and thereby travels a
longer distance.  Yes, I do realize that this would calculate a
vehicle's speed as lower than actual, but it isn't really relevent.
If the evidence obtained has no direct correlation with the
defendant's vehicle, it should not be considered... sure, some judges
might hear it, but it still is garbage.
	So now, are you sure that the CHP actually use such a method?
Seems to me that any reasonable presentable and intelligent person
could take such a case to court and put the Police Department to
shame.  Maybe you should check the facts again, or be happy that you
know that you'll get off if stopped this way.
 
				- Jason
-- 
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 \ Skidmore College \ Saratoga Springs, NY 12866 \ 518-581-6580 \  
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