Imagine a child lost in a national forest, missing for hours. Search and rescue professionals might scour the area by vehicle or foot, or fly a helicopter overhead in hopes of spotting the child. The limitations of such efforts are obvious—vehicle or foot searches can be painstakingly slow, while trees, brush, rocky terrain, and bodies of rushing water can impede progress. Helicopters, likewise, can only fly so low. Spotting the child depends on luck and how well the pilots can see.