That all changed when scientists began using lidar, a remote sensing technique that shoots lasers from low-flying planes. By measuring a laser's travel time, scientists can determine the shape of the ground within a few centimeters and create a picture of the landscape stripped bare of vegetation. In Central America, the technique has exposed thousands of structures previously concealed by the forest canopy. The latest study used lidar to uncover a network of ancient canals and farming fields in the low-lying wetlands of northwestern Belize.