In other words, lidar is the same as radar, except the energy source, a laser , is in the optical part of the electro-magnetic spectrum. Range Finder Conceptually, the simplest lidar to understand is the range finder, like the one used on the battle field to determine distance to an enemy tank. In a range finder, a laser sends out a pulse and a receiver, often little more than a lens, a detector, and some electronics, registers a pulse when reflected light is incident on the detector. An altimeter is a kind of range finder.
More sophisticated systems work off of the same principle as the range finder.
By adding multiple receivers at different locations and triangulating the results, the target can be accurately located in 3 dimensions. Alternately, by adding a scan mirror to the laser output , the beam can be directed to various parts of the target. By determining the small differences in distance to the target, the surface contours can be determined. At the current time, this technique is only useful to look at the gross features of large objects. Similar information can be determined by replacing the detector with an array.