We're all used to Google Earth and the phrase "large enough to be seen from space" has little meaning now when you can see my patio furniture on Google Earth. But, high quality satellite images have been generated since the 1960s. Many of these have been declassified and are available on the US Geological Survey's Earth Explorer website. These images are not restricted to the US - they're spy photos so the whole world is pretty much covered. The interface takes a bit of figuring ou t but there are a lot of resources available on the site. Many researchers, such as archeologists, are finding these images very useful, as is reported in this National Gepgraphic article.
from The Universal Machine http://universal-machine.blogspot.com/