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Author Topic: Can spy satellites read number plates from space.
skeptic
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I know it sounds silly, but I've heard is many times, that the cameras on government spy satellites can read a number plate from orbit in space.
I realise the various agencies will not divulge how good their technology is, but how true is this likely to be.

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First of Two
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Well, check out the highest resolution on Google Earth, and then consider that spy satellite imagery is probably at least one order of magnitude more sophisticated.

I believe the best spy satellites currectly have resolutions of about 10cm, however, which would be too weak to read a license plate accurately.

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stalker
Deck the Malls


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Wikipedia says the resolution is possibly down to 4cm.

When they pass laws that require us to have number plates on the roofs of our cars we'll know the technology is good enough.

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Malruhn
The "Was on Sale" Song


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I got to take a trip on a P-3 Orion Navy reconnaisance plane to do arial surveys of Katrina destruction. On the way back from Louisiana, they started to play with the cameras and such - and showed me some tricks.

On some flavor of active radar camera, we could see every contour of a fishing boat out in the Gulf of Mexico - down to where labels were pasted on the sides of drums - and could read the labels of the sticky letters that were stuck to the life-rings (it was all in gray-scale - no colors).

We were well over 100 miles away from the vessel.

I have no doubt that spy satellites can not only read a license plate - they can tell the orientation of the heads of the screws that are holding said license plate on your car!

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RangerDog
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Remember in the 60s Life Magazine (I think) published a picture of a Russian soldier sitting under a tree smoking a cigarette. You could read the brand on his pack.

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Troodon
It Came Upon a Midnight Clearance


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I think it should be possible to calculate the resolution of a perfect camera of a given size (and I assume that spy cameras are nearly perfect), although I can't do such calculations.

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Jason Threadslayer
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quote:
Originally posted by RangerDog:
Remember in the 60s Life Magazine (I think) published a picture of a Russian soldier sitting under a tree smoking a cigarette. You could read the brand on his pack.

My father has told me (a few years ago) that if you're sitting in the park, smoking a cigarette and reading a book, the US/USSR spy satellites could tell everything but the brand of cigarette you're smoking.

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Nick Theodorakis
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The angular resolution for a telescope (which is what a spy satellite is, essentially something like the Hubble Space Telescope pointed down) is approximated by:

R = λ/D

where R is the angular resolution in radians, λ is the wavelength of light that is being imaged, and D is the diameter of the telescope.

Now, the details of the the latest spy satellites are, of course, classified, but it's believed to have about a 4m diameter mirror (similar to the HST).

So, plugging 4 m into the equation above (and using 400 nm as the light wavelength imaged, which is for convenience of calculation but probably low, as that is almost UV), we get that the angular resolution is:

10-7 radians (about 20 milliarcseconds)

So, what level of resolution is that on the ground?

Let's blow the dust off our old trigonometry texts, and draw a skinny right triangle with the pointy end that has angle R at the satellite, the adjacent base is the altitude of the satellite, and the unknown small length x is on the ground, which is the resolution that we want to solve for. We don't know the altitude of the satellite, but I doubt it's less than 100 km (at least it won't be for long). If I remember my trig memnomic sohcahtoa right, that means that:

tan[10-7 radians] = x / 100000m

I get that x is about 0.01 m (or 10 cm).

So such a satellite could not read a license plate, much less a cigarette carton.

Nick

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NovaSS
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No they can read plates. Cant say were I learned this though. They have drones and other craft that can.
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Singing in the Drizzle
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You also have to add in distortion do to water and other cemicals in the atmosphere the farther you have to look thru it the worse it getts.

My father has spent quite of bit of time working classifed goverment work. All he would say is yes they can read the headlines on a news paper from space, just not easly. The conditions have to be just right. Like the satilite has to be directly overhead and the weather need to very hot with a very low humity. When asked about atmospheric distortion all I get is "There are things they can do". Mind you I never get any real details what he saw or did.

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Don Enrico
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quote:
Originally posted by NovaSS:
No they can read plates. Cant say were I learned this though. They have drones and other craft that can.

I definitly can imagine drone- and airplane-mounted cameras reading numberplates (and even smaller letters, let's say newspaper headlines). The question in the OP, though, was about satellites, and Nick Theodorakis' calculation convinces me that those can't read numberplates. Additionally, satellites - as opposed to airborne vessels of all kind - point their cameras directly down, so they would be able to read a numberplate only if it was pointing up.

Don Enrico

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Troberg
Angels Wii Have Heard on High


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quote:
So such a satellite could not read a license plate, much less a cigarette carton.
And that's just raw resolution in vacuum. Add atmospheric haze and you lose some more.

Then, of course, satellites are shooting more or less straight down. Not much can be seen on a license plate from that angle.

This is also the main reason spy satellites are not in geosynchroneous orbit above nudist beaches.

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/Troberg

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Hans Off
Markdown, the Herald Angels Sing


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quote:
Originally posted by Nick Theodorakis:

....

So such a satellite could not read a license plate, much less a cigarette carton.

Nick

But "Some" sattelites flying in formation would increase the resolution dramatically!

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Don Enrico
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quote:
Originally posted by Hans Off:
quote:
Originally posted by Nick Theodorakis:

....

So such a satellite could not read a license plate, much less a cigarette carton.

Nick

But "Some" sattelites flying in formation would increase the resolution dramatically!
But, since they are pointing straight down, these satellites would need to be very close to each other in orbit to have overlapping image areas.

quote:
Originally posted by Troberg:
This is also the main reason spy satellites are not in geosynchroneous orbit above nudist beaches.

Taking in consideration that people don't tend to stand around on nudist beaches, there would be something to see from above ...

Don Enrico

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My spelling is Wobbly. It's good spelling, but it Wobbles, and the letters get in the wrong places. - Pooh Bear

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Troberg
Angels Wii Have Heard on High


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quote:
Taking in consideration that people don't tend to stand around on nudist beaches, there would be something to see from above ...
At 10 cm resolution, I'd prefer the internet for porn. "Wow, look at those huge tits, they must be almost two pixels!" Nope, doesn't work.

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/Troberg

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Hans Off
Markdown, the Herald Angels Sing


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quote:
Originally posted by Don Enrico:
But, since they are pointing straight down, these satellites would need to be very close to each other in orbit to have overlapping image areas.


Don Enrico

No, not if you use a virtual mirror technique like the VLA etc.

besides, why would they have to be pointing straight down? I haven't launched them yet!!!!

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Malruhn
The "Was on Sale" Song


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So how was the crew of the Navy recon plane able to get such detail at well over 100 miles LATERALLY with RADAR, and not even photographs?

With the resolution I saw, you could easily pick out letters/numbers the size you find on a license plate - though I won't make a claim as to state/county on the same plates.

But I wouldn't be surprised.

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Delta-V
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quote:
Originally posted by Troberg:
Then, of course, satellites are shooting more or less straight down. Not much can be seen on a license plate from that angle.

You can rotate the satellite to shoot from a low angle. But the additional atmospheric distortion degrades the resolution. I think that's the primary problem to overcome when trying to resolve a license plate.

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Troberg
Angels Wii Have Heard on High


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quote:
You can rotate the satellite to shoot from a low angle. But the additional atmospheric distortion degrades the resolution.
As do the added distance.

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/Troberg

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DesertRat
It Came Upon a Midnight Clearance


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The prior and current servicemembers posting their experiences here really ought know better than to comment on these things.

ETA: Not being snarky, just saying...

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AnglsWeHvHrdOnHiRdr
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As a former servicemember, I can tell you everything I know about such things in precisely zero words.

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abbubmah
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quote:
Originally posted by Malruhn:
So how was the crew of the Navy recon plane able to get such detail at well over 100 miles LATERALLY with RADAR, and not even photographs?

The wavelengths of gHz radar are in the tenths of millimeters; that is more than sufficient to produce the kind of resolution you are talking about. However, accuracy of pointing, and a very sophisticated receiver are required.

Tricky from an airplane. Very interesting! Inability to read labels is simply there is not enough height to the ink. They are for all practical purposes, flat.

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Mr. Billion
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quote:
Originally posted by First of Two:
Well, check out the highest resolution on Google Earth, and then consider that spy satellite imagery is probably at least one order of magnitude more sophisticated.

Most (or possibly all) of the highest-resolution imagery in Google maps is from aerial photography.

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