The Google Earth pics are taken by planes (at least when you zoom in. If you want to see the resolution of the satellite imagery, check remote rural areas).

Spy satellites probably have better resolution than this (but most likely nowhere near as good as they would like us to think they have), but as you point out, they can only pinpoint a small area to view.

But if you want to see a man walking his dog last Wednesday, the best place to look is one of the ubiquitous CCTV cameras in most major cities now... and these are used for all the reasons you listed (except maybe sports arbitration - what on earth is that?)

thank you! Didn't know the high definition in google earth was taken from planes!

Sports arbitration was just for fun lets say to check if the ball went over the line...!

OK so the technology isn't there! TA

How often Google Earth update the photos ?

I don't think so,

With 10 cm resolution you would not be able to read a license plate.

You need to be able to resolve at least the width of the line of the text used to write the numbers on the license plate.

To read a license plate you would need about 10 mm resolution.

The reading resolution doesn't need to be as fine as the line width. Just good enough to detect whether there is one line or two - and even there you don't absolutely need to see a clear white in between. This is because you already have a good idea what the possibilities of apparent heaviness, width and location are for blurred letters, and all you need to do is decide which is most likely. This technique is used in astronomy to discriminate stars that are considerably closer together than they can technically be resolved (the trick here is to match the blurred image with what would be produced by a number of "point" sources.

Of course, the further you go down this path the more readily the information can be corrupted by a spec of dust...

The answer is yes. The problem is that's a crapload of data to store. And clouds can be a problem. And then there's the privacy issues.

A simpler solution is local surveillance cameras.

oK yes of course so only a small area can be pin pointed at any one time

but therz is nothing yet that is recording in fine detail everywhere all the time

id say it will happen soon enough though

Yes, don't go sunbathing naked in your backyard it could induce a national crisis

"they have missiles!"

Why bother with those modified X rays in the airports (that will become another thread)

License plates can be read, though they seldom are as spy satellites are in low orbit and have a limited lifetime because of that, therefore far too expensive (usually) to track cars!!

I should add that reading license plates was achieved many years ago......what they can do today will be better....

Also, using IR, clouds do not block vision as they used to.......

The up to date versions and their capabilities are of course top secret!!

No. A guy walking a dog does not stir enough interest for any nation with a spy satellite to observe.

That would depend on who the guy (and the dog) is. I've read they have tracked individual Taliban members around, with good enough resolution to recognize them.

yes, but... don't forget that they used such technology (cameras in the sky) to kill "Osama Bin Laden"... turns out they just blew up some tall guy and his mates... so they aren't quite at the "recognise them" stage (except that your average missile jockey probably thinks they all look the same anyway).

No mention of any of the alleged terrorists walking a dog, cat or pet of any kind, so we're still waiting for confirmation on that one.

http://news.bbc.co.uk/1/hi/world/americas/1813337.stm

ok so a guy walking his cat!

that was just to suggest the sort of detail wanted

but from previous feeds it seems a lot more detail can be achieved

anyway my initial querry was to find out if just one satelite could "spy" in great detail (man n cat) everywhere at the same time all the time.

by the way we need to stay technical here dont we?

can anybody suggest what spec of Lens would be necessary to record lets say NY city in such detail that lets say some time after a specific (outdoor!!!) event we could look at the footage and zoom in to see some man murdering.......his cat in central park!

I went to college back in the '70's. There was a professor at our college that had worked for US Airforce reconnisance in the '50's. At that time they had cameras on the spy planes that could distinguish the stitching on a football at 100,000 feet. I'm sure capabilities are an order of magnitude greater now. Still, cameras can't focus on everywhere at once, and the enormous amounts of data trying to get high resolution images of just one small city would be staggering.

Flower power, it started in the 60's.......

The limitation of resolution is determined by the Rayleigh criterion, when the diffraction of light from 2 adjacent points obscure each other.

This is a function of wavelength and aperture, ie the bigger the lense/mirror diameter, the better the potential resolution. Sorry I can't remember the formula, I'm sure it is somewhre in one of my old (ancient?) text books.

The limitation on the detail a sattelite could potentially see is basically an optical one, although a good observer can make some remarkable guesses when you get beyond what can be resolved. Presumably, some of the computer enhancement programs can help to, but the basic optical limit remains.

Of course, with no gravity to distort it, the potential diameter of a mirror in space could be enormous.

If anyone wishes to have a copy of small movie taken (illegally) from a US bomber circling at about 30,000 feet over Afghanistan about 10 years ago (exactly when I haven't a clue, but I have had a copy for a fairly long time!), as it drops bombs on Terrorists on an individual basis, send me your actual email address over CR4 email.....

I am sure that the possibilities for satellites are probably equal today as IR imaging (as in this film taken at night) have made huge strides in accuracy and detail.

Would you agree that spy satellite resolution is more likely economics vs. utility than raw technological capability? The issue being the trade-off between lens size (for a fixed resolution on the ground, the lens diameter needs to grow proportionally with height), image diameter (presumably field of view is also important) and camera weight.

But perhaps the more important advances will be in selective image compression, as there's no point in gathering an ultra-high-resolution moving image over a large field of view unless you can transmit the important bits to your base.

utility? the info could be sold for billions to insurance businesses alone (looking at car accidents for instance to determine liabilities)

that said if the lens has to be the size of a footabll field well its simply not possible but who knows in 20years time...

Not quite that big - depending on specific wavelength, 10-m diameter would be good enough for 10-cm resolution, and the first focussing element could be a reflector and so quite lightweight.

10CM resolution over how big an area?

could it look down on a whole city with 10cm resolution?

I assume that you mean simultaneously? In practice, these low-earth-orbit systems scan over the ground, so even simultaneous cannot mean continuous. The aperture need not increase with field of view, but in practice the length of the optical system will; however, that's probably not such a problem in space. What is significant is the necessary size of the receptor. If we choose a 20-um pixel, at 10-cm resolution the receptor size will be 20-cm/ground_km. Quite large, but not out of the question.

With the US military, cost bears almost no part of a decision.....if there is a need, they will have it no matter what it costs.....

So I do believe that I can answer your question as:- "yes, raw technological Capability" is required.

I suspect much of the claimed resolution is essentially hype designed to have potential enemies afraid that everything they have or do will be seen.

Having said that, computer enhancement enables them to push the Rayleigh limit of resolution and large reflectors in space don't have to be of glass so big apertures should be possible. How big? depends on what the military regards as needed. They will find the money if they think the need is there and hide the cost somewhere if it's not in the budget.

I GAed your answer, your name is also perfect!!

Have a great weekend.