The team used two autonomous octocopters to fly multiple routes outside a small, four-walled brick building. One of the drones continuously transmitted a wireless signal, while another measured the strength of the signal as it travelled through the structure. After several passes, the data was processed through imaging algorithms developed by the researchers to create a 3D picture of the interior.
"Our proposed approach has enabled unmanned aerial vehicles to image details through walls in 3D with only WiFi signals," said Yasamin Mostofi, a professor of electrical and computer engineering at UCSB.
"This approach utilises only WiFi RSSI measurements, does not require any prior measurements in the area of interest and does not need objects to move to be imaged."
The research, which was presented at the International Conference on Information Processing in Sensor Networks (IPSN) in April, builds on several years of work at the Mostofi Lab. Using everyday radio frequency signals such as WiFi, the professor and her colleagues have been developing imaging technology since 2010, including a 2D method involving robots working in tandem.
"However, enabling 3D through-wall imaging of real areas is considerably more challenging due to the considerable increase in the number of unknowns," Mostofi explained.
Creating a 3D image was only possible due to the drones’ ability to capture signal data from a variety of angles, as well as updating the imaging methodology applied to the data. According to the researchers, the technology could have applications in search & rescue, archaeological discovery and structural monitoring.
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