# How High?

interzone55 21:11 09 Dec 09
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I've just been sent some info about a US CCTV camera that claims to offer identification at 20km and usable IR lighting for 2km.

Now my elementary maths is failing me, so can anyone help me work out how high this camera must be mounted, allowing for the curvature of the earth, to allow it to see a man 20km away?

Kevscar1 21:45 09 Dec 09

Is the man standing on a hill or level ground

mr simon 22:04 09 Dec 09

1.17 times the square root of your height is the equation I think.

mr simon 22:08 09 Dec 09

Which would make it about 68 metres high.

Forum Editor 23:05 09 Dec 09

would need to be mounted on a tower about 250 feet high.

BT 08:05 10 Dec 09

..you are both almost in agreement.

However as you can see the French coast on a clear day, from Dover a distance of 21 miles, and 20km is only 12.4 miles I don't think you really need a tower.

morddwyd 09:00 10 Dec 09

White cliffs will do just as well!

mr simon 10:04 10 Dec 09

I would think FE's estimation is probably right, I worked mine out in nautical miles.

interzone55 11:27 10 Dec 09

Thanks everyone, I was thinking around 200 feet.

It'll need to be a very strong tower, or the camera will be unusable...

BT 16:45 10 Dec 09

Maybe they're standing on top of the cliffs!

Simsy 16:45 12 Dec 09

with a good diagram about half way down.