1 The location of ancient ruins can pose a challenge for archaeologists who wish to excavate and understand them. For example, reaching the Mayan ruins at Caracol on the Vaca Plateau in Belize initially required hiking to a remote location within a rain forest. But with a measuring technology called lidar (light detection and ranging), archaeologists can produce a highly accurate three-dimensional map of 80 square miles of rain forest in a few weeks. 2 Lidar is similar to radar, which measures distance by sending out radio waves. Radio waves from a radar device travel to the target area at the speed of light (300 million meters per second) and bounce back. The device measures how long the round-trip takes. The duration of the round-trip is multiplied by the speed of light to calculate the total distance the radio waves traveled to and from the target area. 3 Instead of using radio waves, though, lidar uses a laser to send out pulses of light in the infrared to ultraviolet range. To map the Mayan ruins at Caracol, an airplane flew back and forth over the site while the lidar device fired 50,000–150,000 laser light pulses per second. These pulses reflected off the target area, including some pulses that penetrated the forest canopy. When the pulses returned, the lidar device detected them. At the same time, a global positioning and navigation system recorded the airplane′s position and orientation in the air. Using this information, lidar calculated the distance from each object it scanned, and thus each object′s elevation. The graph shows an example of raw lidar data collected during this study. The data were generated from any object that caused the lidar light pulses to be reflected off the target area, such as trees or human-made structures. 4 In addition to its use in archaeology, lidar is used to map geologic faults, flood plains, and coastal areas. It is also used in forestry, transportation studies, and ocean research.