What kind of optics do...
Posted 14 February 2013 - 12:16 AM
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!
Posted 14 February 2013 - 02:16 AM
Posted 14 February 2013 - 06:20 AM
Posted 14 February 2013 - 10:06 AM
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......
Posted 14 February 2013 - 01:21 PM
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.
Posted 14 February 2013 - 01:34 PM
Posted 14 February 2013 - 01:42 PM
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).
Posted 14 February 2013 - 05:52 PM
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.
you'd be surprized at the optics available to them and the capabilities they have.
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.