Declassified spy images used to discover ancient sites.

Interesting article related to my OP.

Google Earth is now being used by archaeologists more than the NASA, IKONOS and NRO and CORONA satellites photo's which have been declassified. Apparently the declassified spy satelite images can cost 10's of thousands of dollars whereas the Google Earth images cost very little in comparison.

cosmosmagazine

The human eye can detect wavelengths of light within the range of around 400 to 700 nanometres. But cameras attached to satellites and aircraft are now taking infrared and ultraviolet shots over a much wider range of wavelengths – and revealing some remarkable details about ancient civilisations.

It is not always changes in vegetation that reveals a hidden structure. Every object in the universe continually emits electromagnetic waves, such as light and infrared. The wavelengths emitted depend on the material and the temperature of the object.
Sensitive detectors, on satellites or aircraft, can reveal slight differences in ground cover through tiny variations in temperature. So if a region contains more stone, water or wood than its surrounds, it will stand out in a multi-spectral image.

Within a few hours on Google Earth, Madry was able to locate 101 features in an area covering 1,440 square kilometres in Central France. These features represented Iron Age, Medieval and Gallo-Roman sites.