I would love to see an update to this column. Since it was written, it would appear that commercial satellites have improved their resolution by orders of magnitude (see, e.g., Satellite imagery - Wikipedia). I wonder if spy satellites have gotten any better, or if the 6 inches that Cecil spoke of is close to the theoretical limit based on atmospheric distortion.
Pre-apologies for a useless response, but I remember in a high school physics course we worked-through this problem, matching the minimum size of the lens required to get a resolution of X inches, taking into account atmospheric distortion, etc.
The conclusion we came to was that if it were possible to build a satellite that could get a, say, 1 cm resolution, its lens would be so huge it would be easily visible from the ground, and very bright-- it wouldn’t be a secret, in other words.
Since there are no easily-visible huge lenses in the sky at night, it’s safe to say a satellite with that resolution doesn’t currently exist.
But there is now image enhancement.
While that (outside of movies and TV) is somewhat limited, I have heard of using multiple lenses, separate lenses and cameras to get higher resolution than from just one.
Wouldn’t it be more plausible just to use a plane or perhaps a human spy to report the headlines? Or maybe even visit the newspaper’s website?
I don’t think anyone is seriously interested in determining headlines by satellite. It’s more about what else they might be able to make out/read.
That said, airplanes and human spies are probably better for some things. Much closer view, much finer resolution. However, satellites aren’t low enough to get shot down (like the U2 spy plane incident), and don’t give themselves away as easily (say, spying on terrorist training camps).
Yeah, things have changed. Multiple mirror telescopes, adaptive optics, etc.
Astronomy scopes are big on using laser guide stars. But I think if you’re reading a paper on a park bench and suddenly the page lights up red, you’re going to notice it.
The old Rayleigh criterion back of the envelope calculations don’t really apply anymore.
Don’t they have adaptive optics now as well that can compensate for atmospheric distortion? My WAG is that there have been incremental increases in resolution, but that the commercial stuff has just caught up to where spy satellites were when the article was written, but that the spy satellites still couldn’t read print.
Be interesting if Cecil did an update on this one though, if there is new information available.
ETA: I wrote the above earlier today and didn’t post…sorry, ftg has already mentioned the adaptive optics part.
-XT
One thing I wonder, I take it all the calculations performed and the 6 inches theoretical resolution is based on sea level cities. If this is the case then newspapers in La Rinconada (Perú) [The highest city/town in the World according to National Geographic Magazine] are more than readable with aforementioned satellites.
If modern satellites have improved, it doesn’t seem like they improved very much. This article boasts about resolution down to 4 inches or 10 centimeters.
Does it matter?
If you can see things down to 4-6 inches in size, nearly any military installation would be visible. Heck, they could tell if I had picked the rhubarb in my back garden!
Doesn’t seem like it would be worth the effort to try to develop a higher resolution than this. Especially in light of the effort needed to analyze such photos. Doubled resolution would mean a doubling of the people-time needed to view these photos, looking for important information.
I doubt that 4 inches is good enough to recognize faces. I’d imagine that the ability to know that a given person is (was) at a certain location would be extremely valuable in many situations. And as facial-recognition software improves, “people-time” becomes less and less of a factor.
This question, being 24 years old at this point, must surely deserve an update. If the Hubble can see into other galaxies, I’d think orbiting satellites could practically see your DNA by now. So, Cecil, what’s the 2011 straight dope on this one??
I suspect (but have no data) that the imperative for recognition of individuals by face or other criteria has largely disapperared from orbital technology due to the relative cheapness and flexibility of drones.
Use orbital for the big stuff (no resolution needed beyond 10 cm) and drones for tactical stuff, cheap, carry nasty payload, etc.
I would guess that, unless the person in question looks straight up, facial recognition from a satellite isn’t going to work no matter what the resolution.
Two points:
- Drones do that, are cheap, and disposable (more or less).
- Unless you’re very lucky, the angle on the satellite isn’t going to show you the face even if it had enough resolution. A drone can get a good angle on him.
Not the same thing at all. Hubble can see HUGE things very far away, because they are HUGE.
Drones aren’t exactly disposable or cheap. But they are cheaper than satellites, and much more flexible than satellites, and they are far more disposable than people (pilots, spies), and much easier to replace than satellites.
(Actually, some “drones” they use now may not be much more than commercial RC planes with cameras attached. Hmmm.)
If a piece of this thing lands in my yard I’m keeping it. I’ll test it for radioactivity with my geiger counter and if it passes I will cover it with junk. If someone disposes of junk on you’re property than you should have the right to keep it if you want or press charges if you do not like it.
Please to inquire, what are you talking about? I don’t understand this at all and don’t know that it’s relevant to the column.
Sorry, I thought this article was about the satelite that was falling out of orbit on the 26th. I don’t see what I saw that made me think that.