KATHMANDU: LiDAR is the integration of three technologies into a single system capable of acquiring data to produce accurate digital elevation models. These technologies are lasers, the Global Positioning System, and Inertial Navigation Systems. Combined, they allow the positioning of the footprint of a laser beam as it hits an object, to a high degree of accuracy. A LiDAR system combines a single narrow-beam laser with a receiver system. The laser produces an optical pulse that is transmitted, reflected off an object, and returned to the receiver. Helicopters are used for taking the data and images. The system can record "multiple re­turns" from the same pulse. In such systems, the beam may hit leaves at the top of tree canopy, while part of the beam travels further and may hit more leaves or branches. Some of the beam would likely hit the ground and be reflected back, ending up with a set of recorded multiple returns.