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What kind of optics do...

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#1 orion61



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Posted 14 February 2013 - 12:16 AM

I am wondering what kind of optics the Satellites use for Google Earth?
If you havent used it in awhile I suggest you download it for free, Icouldn't believe the resolution!
I could see the pile of leaves in my pickup from last year!
I could even detect my A/C unit! Amazing.. Just imagine what is up there we DON'T know about!

#2 WarmWeatherGuy


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Posted 14 February 2013 - 02:16 AM

I think many of the photographs are taken from an airplane. I've seen pictures where you can see the reflection of clouds in the lakes below but there are no clouds to be seen. This is what you see when you are in an airplane below some clouds.

#3 iluxo


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Posted 14 February 2013 - 06:20 AM

Google Earth uses aerial photography commissioned from various sources in each country. If you use the Google Earth app on a desktop computer the copyright holder for the imagery is usually acknowledged somewhere on-screen.

#4 csrlice12


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Posted 14 February 2013 - 10:06 AM

.....and just what were you up to with those leafs that satellite time was used to spy on you......... :question:

You weren't trying to hide a scope under that pile of leafs were you?? The Cloud Gods don't like it when you try and fool them......

#5 Eddgie


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Posted 14 February 2013 - 01:21 PM

I thought that the primary source of Google Earth images was from their own source.

They purchased a company called Keyhole (previously an vendor to the CIA) about 7 years ago.

The topography mapping (terrain) was produced by the Space Shuttle. The Shuttle did a Space Shuttle Topography Mission (SRTM Mission).

I believe that they also purchase images from other satellite companies, and they also use some aerial images.

The only earth imaging satellite that I have detailed information on is QuickBird.

Quickbird uses a 60cm (24") reflector with a focal length of 8.8 meters (f/14.7) providing a FOV (Field of View) of 2.12º, obtained with an unobscured off-axis three-mirror-anastigmatic (TMA) optical form.

This same design (in different sizes) has been used in other earth imaging satellites.

Now there are no doubt other designs out there, but for this kind of use, it would appear to me to be likely that some kind of folded optical design makes the most sense because it can be packaged in a small format, and if it goes into space, size is weight, and weight is expensive to get into orbit.

Kodak built the camera I believe.

#6 csrlice12


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Posted 14 February 2013 - 01:34 PM

Having worked with companies who build sattelites for the DoD, NASA, NOAA, etc...you'd be surprized at the optics available to them and the capabilities they have. And, there are a number of them up there. Orbimage does a lot of commercial satellite photo work (along with Government work too). There's a big satellite and optics industry in Denver.

#7 Eddgie


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Posted 14 February 2013 - 01:42 PM

A follow-up to my previous post.. The description of the telescope above may be a Schiefspiegler but the engineering drawings I have seen suggest that it is not a Schiefspiegler and this is consistent with the focal length. The Schiefspiegler would have to be around f/30.

Some of the papers I have read suggest that there is a correction component to the tilted mirror, which makes it very likely that it is some highly aspheric design.

The Schiefspiegler has to have a very slow focal ratio to keep the coma inside the diameter of the Airy Disk.

So not a pure Schiefspiegler but likely some variation with some kind of corrector somewere. Again, I have read some patents on these that suggest that the correction is in one of the mirrors, but a cutaway diagram of one of these I saw has a big stack of lenses between the diagonal mirror and the sensor, so perhaps it is somehow done there, though several patents mention correction being done by one of the mirrors (aspheric or some other curve).

#8 Mike B

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Posted 14 February 2013 - 05:52 PM

you'd be surprized at the optics available to them and the capabilities they have.

Okay, Wiki says the lowest practical orbit is ~600 miles. That's gotta be bookin' pretty fast relative to the ground... we probably see these all the time flitting thru the EP as we observe. I know i do... north-south birds.

If such a bird has a 24" scope, and it's able to magnify at 50x per inch- that's 1200x; so same resolution as looking downward from half-a-mile. That ain't reading no newsprint headlines.

Okay, let's say they're getting 100x per inch. Now it's seeing as if at a quarter mile up... ~1,400 feet. I know what *i* can see from 1,400 feet, terrestrially speakin'- squat. It's a car, truck, or SUV, tan, maybe a Ford... late 90's.

Just how far are they able to enhance these images?

I know, i know... not s'posed to ask such questions.

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