I've heard that Osama Bin Laden was first found via satellite. I was wondering if it is possible to have a satellite that can scan an entire continent and find a single person or terrorists without having any specific location to look for? Can sattelites be that powerful?

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    $\begingroup$ Not a space exploration question, but cameras on satellites don't have nearly enough resolution to do facial recognition of people on the surface of the Earth. You could make out individual people under ideal conditions, which might be useful in searches if they're somewhere you weren't expecting people to be, but that's it. OBL was almost certainly located via human intelligence. $\endgroup$ Sep 6 '17 at 0:31
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    $\begingroup$ This Wikipedia page might help to answer your question. $\endgroup$
    – Anthony X
    Sep 6 '17 at 0:57
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    $\begingroup$ @RussellBorogove for some reason Is it possible to see animals from space? gets 30 up votes and three good answers including First count of individual birds from space & First complete count of an entire species population from space so perhaps there may be some leeway? We have several questions about limiting resolution due to both atmospheric (seeing) and diffraction effects, and questions about data rates and on-board computing power. So maybe a good answer to this question can be derived/duped $\endgroup$
    – uhoh
    Sep 6 '17 at 3:09
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    $\begingroup$ I agree with @uhoh -- there's an opportunity for a really good answer here if someone is willing to put in the effort. $\endgroup$
    – Chris
    Sep 6 '17 at 3:19
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    $\begingroup$ @RussellBorogove SIGINT was also important and satellites play a crucial role in that. Geolocation of particular cell phones without cooperation from the cell network is common practice. $\endgroup$ Sep 6 '17 at 6:05

I've heard that Osama Bin Laden was first found via satellite.

That isn't the case. Bin Laden was instead first found by human intelligence (interrogation, spy work). Detainees at Guantanamo revealed the name of bin Laden's most trusted courier. This eventually led to that courier being found and then discretely tailed to the compound in Abbottabad. It was suspected that someone of greater importance than a courier lived in the compound. Satellite recon was used in the process, but to develop a 3D map of the compound rather than to recognize bin Laden. Photographs of someone suspected of being bin Laden were taken, but by drones, not satellites.

Can a satellite scan an entire continent to search for someone?

No, for many reasons.

One reason is the resolution limitations of a satellite due to physics. Geostationary satellites can see almost half of the globe, but the large distance between those geostationary satellites and the surface of the Earth places severe limitations on resolution. Reconnaissance satellites (aka spy satellites) operate in low Earth orbit to overcome these limitations, but even then, the resolution is estimated to be about ten centimeters. That's not enough resolution to recognize that a face is present, let alone who's face it is.

Another issue is that those reconnaissance satellites can only see a rather small part of the globe. It takes multiple days for a reconnaissance satellite to fully map a continent. The person subject to the search can hide indoors (or simply not look up) during the very brief intervals when the satellite is in view.

Yet another issue is the huge amount of data needed to accomplish this task. Assuming good conditions, assuming the person subject to the search walks around looking up, and assuming a satellite with 0.4 centimeter resolution exists (the resolution needed for facial identification under good conditions), a continent's worth of monocolor (grey scale) imagery represents over an exabyte of data. Many such images will need to be scanned to find the elusive person of interest. Even the most powerful supercomputer is not up to this task.

  • $\begingroup$ Several years ago, before drones became a thing, a DoD contractor friend of mine told me that whenever they do tests out in AZ they are required to be under some sort of structure whenever typing on a computer or writing on paper. I thought it ridiculous because we couldn't even read license plates with satellites, but he stated those rules were explicitly defined by the military. I think it was just typical overly cautious military procedure but he believed that there were legitimate threats. I have always wondered what limits nonlinear optics could hold but perhaps not enough... $\endgroup$ Sep 8 '17 at 17:39
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    $\begingroup$ @honeste_vivere that was also before the ubiquitous indoor ceiling-mounted security cameras became a thing. It's not "safe" to type anywhere now ;-) $\endgroup$
    – uhoh
    Sep 8 '17 at 18:23

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