How advanced is the current satellite based photography of earth?

[Lat-Literal]

I ask this question because it always surprises me when an aircraft goes missing or a chemical attack occurs and no one is certain what happened.

I would have thought that advances in technology had been such that it would be possible to pinpoint what was taking place on every blade of grass.

[Dave2002]

If like many of us you live in the UK you must have noticed that peculiar phenomenon known as a cloud!

You can estimate how good satellite photography is by looking at Google maps. I think the resolution now possible on clear sky days is much better than that you can see in Google maps.

[Stunsworth]

Well, the world is a big place and a satellite (near enough to pick up detail) has a relatively small photographic footprint (and would be constantly moving). So an enormous number of satellites would be needed.

[Dave2002]

Well, the world is a big place and a satellite (near enough to pick up detail) has a relatively small photographic footprint (and would be constantly moving). So an enormous number of satellites would be needed.

We know that it's possible to have 66 LEO (low earth orbit) satellites orbiting, as that's what the Iridium communications system uses. Each satellite will orbit in about 90 minutes following a polar orbit. That system does not AFAIK do optical monitoring.

If such a system were used for visual monitoring, then each satellite (1 out of about 60) would potentially cover about 6 degrees of the earth's surface, or about a strip of 400 miles per revolution. If the satellites are at a height of H (say 150 miles), then using lenses with a field of view of about 60 degrees (not quite wide angle), then the cameras could cover a strip of about 173 miles, so it would therefore take 3 orbital revolutions for all the cameras on all of the cameras to cover the whole surface of the earth. The totality of cameras could potentially monitor the whole earth in a period of about 5 hours.

Some satellites are GEO (geostationary) and are a long way out - about 24000 miles. Most of the earth can be viewed from GEO satellites, and only around 4-5 are needed to "see" most of the earth, but the poles cannot be viewed from GEO satellites. Obviously there would be a severe resolution problem for cameras on GEO satellites, because of the distances involved.

Some satellites are MEO - medium earth orbit, which may give a compromise between coverage, but low resolution images, and higher resolution images but poor coverage unless many satellites are used.

I would not rule out the possibility that some camera systems already exist which can monitor most activity - but the major problems could still be due to weather.

[Lat-Literal]

Many thanks for those interesting responses. If I understand what is being said correctly, we are still some way from having the entire globe under permanent camera and the maximum current potential is for most bits of it to appear on camera at least once every five hours albeit in low resolution with an absence of detail.

However, given that we can spot a volleyball court in North Korea and the detail on that court, is it possible to have the known trouble spots - eg what I suppose George W Bush would have once called the Axis of Evil - and even serious but politically benign aircraft and shipping accident spots under such detailed scrutiny 24/7?

[Dave2002]

Actually most of us have no idea what kind of hardware or software might be used, or currently deployed. Re my earlier msg 4, using cameras with a 60 degree field of view, even if megapixel cameras were used, would give poor resolution for each image. However, there is perhaps no need to use just one image, or indeed to use wide angle cameras. Cameras with a narrower field of view could be used, and using video camera technology it should be possible to capture 100 fps quite easily. A LEO satellite would traverse about 4.5 miles in a second, so by careful choice of lens and reconstruction software it might be possible to generate higher resolution data from a sequence of frames. Also, some specialist cameras can do frame rates significantly higher than 100 fps. I think it should be possible to get resolution capable of picking out a square or circular object 1 sq ft in area if the sky is clear, though the data storage and communication links would present challenges - but I would hesitate to say it couldn't be done.

[Lat-Literal]

Actually most of us have no idea what kind of hardware or software might be used, or currently deployed. Re my earlier msg 4, using cameras with a 60 degree field of view, even if megapixel cameras were used, would give poor resolution for each image. However, there is perhaps no need to use just one image, or indeed to use wide angle cameras. Cameras with a narrower field of view could be used, and using video camera technology it should be possible to capture 100 fps quite easily. A LEO satellite would traverse about 4.5 miles in a second, so by careful choice of lens and reconstruction software it might be possible to generate higher resolution data from a sequence of frames. Also, some specialist cameras can do frame rates significantly higher than 100 fps. I think it should be possible to get resolution capable of picking out a square or circular object 1 sq ft in area if the sky is clear, though the data storage and communication links would present challenges - but I would hesitate to say it couldn't be done.

Well, that is very interesting.

To take Syria as just one example, if it were possible to have a fairly consistent overview in that way, wars as a consequence of any misunderstanding could be averted.

Consequently, it's pretty crucial.

[Anastasius]

To pick up on one aspect ...missing aircraft..there have been mooted several systems that would keep track of aircraft in real-time but there seems to be resistance to implementing them either amongst aircraft manufacturers/airlines or aviation authorities. Probably money related, at a guess.

[MrGongGong]

I ask this question because it always surprises me when an aircraft goes missing or a chemical attack occurs and no one is certain what happened.

I would have thought that advances in technology had been such that it would be possible to pinpoint what was taking place on every blade of grass.

I wouldn't be surprised if there are folks who know where these "missing" aircraft are but don't want others to know what they know etc
Which is NOT to say that they are stored in the caves at the North Pole by the Illuminati

[Dave2002]

To take Syria as just one example, if it were possible to have a fairly consistent overview in that way, wars as a consequence of any misunderstanding could be averted.

BBC Weather for Damascus suggests clear skies for the next week or so. There'll be satellites along any minute or hour now, and you can probably bet that some of them are primed to gather information - though not necessarily visual - depends on the satellites as mentioned earlier.