The work was done by Stonehenge Hidden Landscape Project, a collaboration between a British team and Austria's Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology.
Here are some sources for more information:
- September 2014 issue of Smithsonian magazine (E. Caesar, "What Lies Beneath," vol 45 number 5, cover photo and pp. 30-41).
- BBC news (http://www.bbc.com/news/science-environment-29126854).
- A video will appear on Smithsonian Television later this month (see http://www.smithsonianchannel.com/sc/web/show/3407073/stonehenge-empire for schedule).