While everybody is justifiably talking about the NSA monitoring programs, maybe it doesn't occur to you that imaging satellites are big business. Google Earth anyone? A lot of those images, especially the really high resolution ones, are taken by hiring small planes to survey areas, but many are taken by satellites. Currently, the US limits satellite images sold to private consumers to half meter resolution. Companies like DigitalGlobe provide images at this scale for sale to private customers. They're also rumored to have higher resolutions that are only sold to the US government.
Another change slipped by without notice last week: DNI Clapper (Director of National Intelligence) recommended that the limit be reduced to half that - quarter meter resolution. The idea is to make US companies more competitive in the global satellite imagery business. DigitalGlobe doesn't compete with the NRO, they compete with French, Chinese, and other companies - just listen to the news chatter about the missing MH370 and the constant refrain of "French Satellites images show"... When the half meter, 50 cm, resolution limit was imposed, it was considered a dream goal; that the commercial budgets would never get there. Today, there is a privately owned platform that achieves 41 cm resolution, and DigitalGlobe is said to be preparing to launch a satellite that will get them to 31 cm resolution.
DigitalGlobe’s newest satellite, WorldView 3, is scheduled to launch this August. The new satellite will fly at an altitude of 617 km, and provides 31 centimeter panchromatic resolution, 1.24 meter multispectral resolution, and 3.7 meter short-wave infrared resolution. That lower, official, resolution is why DigitalGlobe wants the White House to move as quickly as possible.It's worth spending a moment on just what this means. The limit they're talking about is cm is over 9 3/4 inches, and that means two adjacent objects must be that far apart to be resolved as different. "Resolved" has a rather specific meaning in optics and in this case it doesn't mean you could read, say, 10" tall numbers, or see a 10" long object that wasn't also 10" inches wide. A 10 x 10" black number on a white background would show a single dark pixel with lighter ones around it. If you had a 20" AR, for example, on a bench that was three or four feet long and wide, at best it would simply show two pixels as being slightly darker than an adjacent one. My gut feel is it wouldn't be visible, though, because the 10" applies to length and width. A 10" long black rod on a white background wouldn't show up. While a carbine length AR is longer than that new satellite resolution, I still don't think it shows up because it's too skinny. All your life, you've probably heard "they can read license plates from space". This doesn't get you there. You need about 1" resolution for that.
A friend who saw this story said, "just look up and wave". A satellite with 25 cm resolution might know there's something there, but wouldn't be able to tell it's a person and wouldn't know you were waving. That's still some years in the future.
Didn't Patriot Games (the book) have a discourse on satellite imagery where they could distinguish between women by bra size? I think shadows told them that. What resolution would that take? I'm guessing 1/2 of the width of the item under scrutiny.
ReplyDeleteI can't recall if the imagery was digital. Did the satellites formerly drop film canisters for recovery?
Could have just been a fun, fictional story detail, but I had the impression Clancy stuck to the technical facts.
They dropped film up until the '80s, if I can believe what I've read. Snatched out of the air with special aircraft.
ReplyDeleteI don't think I actually read Patriot Games, or at least don't recall that. Probably would take a resolution about 1/4 to 1/2 of the "objects of interest". But I wouldn't doubt real image analysts might have tricks that help, like using shadows or taking pictures at the right time of day.
Now as for what the real resolution of spy satellites is, you've got to know that's very classified. I don't have clue, but I've read people saying everything from 1 or 2 inches to 5 or 6. They can't use that over very wide areas; the world is very, very big taken a few inches at a time. Just ask the crews looking for MH370.
I do imagery analysis in my gig, and use the satellite imagery mentioned. Pretty good summary Si. I have quite a bit of the 0.5m meter imagery on my work computer. You can kinda sorta make out people on the beach, but even if they released the ~0.4m native (Ikonos-2/WorldView2) imagery it wouldn't allow for anything beyond car types - pickup vs sedan.
ReplyDelete0.25m is coming, and it will be nice, but it's still limited when compared airplane-collected imagery. You also have to consider atmospheric issues. The more humidity, particulate matter, etc in the air, the more detail will be obscured with satellite data. Satellite imagery in the desert - nice! Rainforest - hope you catch a lucky pass.
As for the spook birds, NASA was recently gifted two unused spy satellites for research use, with the caveat they could not be used for earth observation. Based upon their primary mirror size, and orbit characteristics of other in-class satellites, it was estimated that NGA could acquire ~4" pixel images. I have some airplane-based imagery at that resolution. Strikingly detailed, but no way you are going to read a page, or even identify an individual.
Pete, first, thanks for the feedback that I got it mostly right. Always good to know when venturing out of your field.
ReplyDeleteI think a common misconception people have is when they hear 4" resolution, their thought process is a 4" object in their hand, which they see at much higher resolution, not that something roughly 4" on a side colors one pixel one color. Now that more and more people have been using digital cameras, scanners, and so on, I think they have a better feel for 4" per pixel.
You are correct in that the color for a particular pixel is the average for all objects contained within the geographic boundary of the pixel. Your description of an AR on a table captured it rather well.
ReplyDeleteThe old "read a license plate from space" rumor is rather silly in that license plates are oriented perpendicularly to the earth so how would that be possible even if the resolutions allowed one to be read if laid flat on the earth? Which if I hazarded a guess would require ~1cm resolution to achieve.
Even if you had a mirror large enough to achieve that resolution (current primary mirrors are 2.8-3.0m to achieve the 4" pixels), atmospheric issues would make achieving such a feat unlikely unless conditions were truly optimal (IMHO).
As for the optic systems on the drone fleet....above my pay grade, but for the Patriot community that would be my biggest concern. They can loiter, fly at variable heights, and likely contain synthetic aperture radar imaging systems which are uneffected by weather conditions, as well as FLIR. Their stealth makes them formidable.