what is this thing?

[never_retreat]

Could be a camera.
Is there any wires hanging out of it or antennas?
How long has it been there? is anyone ever near it?

The green part looks like a case for the thing itself.
The stand is the strange part, it does not appear to be very portable yet it is not permanent.

[CNYCacher]

Wouldn't the inverse square law still apply even to tightly focused beams?

[Hawkmoon]

And the inverse square law only holds in its "standard" sense for uniformly divergent radiation.  As the divergence of a beam narrows, however, the reduction in energy per unit distance is less and less until the beam does not diverge at all --as in a tightly-focused laser beam.  The only attenuation is from other stuff like dust in the air.

Sure, take a naked light bulb and its illumination varies with the square of the distance nicely.  But put a focusing reflector (or lens) on it and the illuminated area is no longer spherical, but in a narrow beam.  The inverse square law still holds, but the distances are greater.  Taking it to the extreme, a perfectly parallel beam will have the same illumination however far away it is measured, except for absorption by and reflection off of "stuff" between the bulb and the point of measurement.

Nope, works the same regardless of whether it's a diffuse radiation or a tight beam. Same thing as MOA for a firearm. The only part of the radiation that's of concern to "you" is the portion of the radiation that actually impinges on "you." At distance 'X' from the emitting source, "you" represents a finite area occupying a finite angle of view -- which angle is almost certainly smaller than the angle of the beam, unless the distance is VERY small.

So when the distance becomes 2X, the area occupied by "you" represents 1/4 the first area, and the power of the radiation is proportionally reduced.

[griz]

I'll check it out closer next week.  I think I would have noticed if it had a cable running from it, but I could have missed it.

[griz]

Checked it out again and found enough info to find them online:

http://www.emx-inc.com/

Apparently it's a security camera although I can't find the specific model (5000).

By the way, the sign on the ground says something like "vehicle search area".

[grislyatoms]

Is it on public (say by a pumping sub-station) or private property?

[griz]

It's on a military base.

[280plus]

I love those radar guns on trailers that SHeriff's department place on streets to get people to slow down. Their biggest unintended consequence is encouraging kids to play in the street- either trying determine how fast they can get on their bike or determining the speed of their fast ball. We had one in front of our house for about a month- until the 12 year old kid next door  broke it with a slapshot.

Yup, I speed up soon as I see one just to see how fast I can get going before I pass it. 

[grislyatoms]

It's on a military base.

Huh.

Not a surveyor's transit, it's too short. Yet it's portable. Battery pack. Optical, obviously.

Rx. Speed egregiously by it and see what happens.

[T.O.M.]

Security camera, probably with night vision capabilities.  My bet, it's some new toy DOD has picked up, but hasn't put on a permament mount of some kind.  Probably transmits to some kind of security operations center on-post, back up for the guards.

Nothing to see here.  Move along.  Move along.   

[griz]

The more I think about it, the more I think it's security theater.  The cable from it runs in to some hedges, and since the median is a small island surrounded by pavement any connection would have to be hard wired underground.  I thought about pulling the cable out to see what's on the other end, but I am scared that I might reel in a bigger fish than I planned for.

[Scout26]

No such thing as perfectly parallel, thanks to that bastard Huygens.  The inverse square law (flux is inversely proportional to distance squared) holds for ALL EM, when in free space propagation, past the Gaussian beam waist (or focus if it's a non parallel wavefront at first).  The best you can do for divergence is lambda/D (for the 1/e point of a perfect Gaussian beam)-- meaning, for X-band radar, (3cm lambda) and a 6cm emitter, the beam is almost 30deg wide!  And if you measure the intensity, it follows an inverse square law.  Now take a huge x-band radar...(AN/TPY-2, SBX). Narrower beam, but still follows inverse square. 

This thread was moving along nicely and then you had to go and bring math into it.


Owwww, my head hurts.