Drone fleets could find lost hikers in forests without using GPS

Drones can already be effective search and rescue tools, but not in densely-packed forests where the tree cover might block GPS signals. Thankfully, MIT has a clever solution: use the same technology that guides self-driving cars. Its researchers have developed drone tech that uses LIDAR to map forests without any use of GPS. Each drone creates a 2D map that also includes the orientations of trees, making it easy to tell where the robotic aircraft has already been as it searches through a specified area. That, in turn, makes it feasible to merge maps from an entire drone fleet and comb large swaths of forest with a minimum of wasted effort.