National Geographic : 2014 Jul
132 national geographic • july 2014 empty space. None of the cavers find this answer satisfying in the least. When I catch up with the scanning team, they are in the cracked mud near the meteorite, not far from the edge of the lake and the sheer face of a limestone wall that leads to the hidden roof of the cave. This is one of 17 scanning stations in Hong Meigui—so many because a laser scanner can see no better around a corner or a boulder than a human can. The scanner emits laser pulses and measures how long it takes for them to be reflected back. Distances are easily determined based on the speed of light. Our model is a Riegl VZ-400, used in architecture, engineering, and mining and now for the first time in caving. It’s a metal cylinder about the size of a human head and weighs 21 pounds, not including its two nine-pound batteries or the tripod or laptop and cables. When running, it sits at about eye level, spinning 360 degrees and taking up to 122,000 measurements per second of everything within a maximum 2,000-foot radius. To set up the scanning station, Walters uses a pocket level to ensure that the tripod is true, orients the scanner with a compass, then pulls a n Society Grant The British-led cave expedition and the rock climbing expedition by Cedar Wright, Emily Harrington, and Matt Segal were both funded in part by your National Geographic Society membership.