A colleague of mine worked with Sarah Parcak (the researcher featured) and says: "They use standard satellite images taken by NASA and then apply various photoshop filters to those images to find subtle differences in the terrain. Egypt works great because the starting palette is so clean. They've tried the same technology in South America and haven't had as much success."

Not sure if this is the exact technique they are using in this article, but it's what we featured in an exhibit on Egypt he worked on.