Three years ago, scientists at the University of California, Santa Barbara used Wi-Fi-equipped ground-based robots to obtain two-dimensional images of objects hidden behind brick walls. Now, using aerial drones, they've obtained 3D images of similarly-hidden objects. The technology could ultimately have applications such as search-and-rescue, archaeological discovery and structural monitoring.

Led by Prof. Yasamin Mostofi, the UCSB team utilized a couple of autonomous octocopter drones, both of which were equipped with Wi-Fi transceivers.

As the two aircraft flew in synchronous paths on either side of a four-sided brick structure, one of them continuously transmitted a Wi-Fi signal, while the other measured the strength of that signal as it was received after passing through the bricks. By analyzing variations in the signal strength, it was possible to ascertain the size and shape of objects hidden within the structure, as they disrupted some of the signal.

While the ground-based robots had only been able to get 2D images, the drones' ability to fly not only back and forth but also up and down allowed them to assess the objects from a wider range of angles, resulting in 3D images.

No prior measurements of the area being inspected were necessary.

There's more information in the video below.

Source: UCSB