Lidar (/ˈlaɪdɑːr/, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object with a laser and measuring the time for the reflected light to return to the receiver. Lidar can also be used to make digital 3-D representations of areas on the earth's surface and ocean bottom, due to differences in laser return times, and by varying laser wavelengths. It has terrestrial, airborne, and mobile applications.
Play mediaLidar is an acronym of "light detection and ranging"[1] or "laser imaging, detection, and ranging".[2] Lidar sometimes is called 3-D laser scanning, a special combination of a 3-D scanning and laser scanning.[3]
Lidar is commonly used to make high-resolution maps, with applications in surveying, geodesy, geomatics, archaeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics,[4] laser guidance, airborne laser swath mapping (ALSM), and laser altimetry. The technology is also used in control and navigation for some autonomous cars.[5]
History and etymology
Under the direction of Malcolm Stitch, the Hughes Aircraft Company introduced the first lidar-like system in 1961,[6][7] shortly after the invention of the laser. Intended for satellite tracking, this system combined laser-focused imaging with the ability to calculate distances by measuring the time for a signal to return using appropriate sensors and data acquisition electronics. It was originally called "Colidar" an acronym for "COherent Light Detecting And Ranging,"[8] derived from the term "radar", itself an acronym for "Radio Detection And Ranging". All laser rangefinders, laser altimeters and lidar units are derived from the early colidar systems. The first practical terrestrial application of a colidar system was the "Colidar Mark II", a large rifle-like laser rangefinder produced in 1963 which had a range of 7 miles and an accuracy of 15 feet, to be used for military targeting.[9][7] The first mention of lidar as a stand-alone word in 1963 suggests it originated as a portmanteau of "light" and "radar": "Eventually the laser may provide an extremely sensitive detector of particular wavelengths from distant objects. Meanwhile, it is being used to study the moon by 'lidar' (light radar) ..."[10][11]
Lidar's first applications were in meteorology, for which the National Center for Atmospheric Research used it to measure clouds and pollution.[12] The general public became aware of the accuracy and usefulness of lidar systems in 1971 during the Apollo 15 mission, when astronauts used a laser altimeter to map the surface of the moon. Although the English language no longer treats "radar" as an acronym, (i.e., uncapitalized), the word "lidar" was capitalized as "LIDAR" or "LiDAR" in some publications beginning in the 1980s. No consensus exists on capitalization. Various publications refer to lidar as "LIDAR", "LiDAR", "LIDaR", or "Lidar". The USGS uses both "LIDAR" and "lidar", sometimes in the same document;[13] the New York Times predominantly uses "lidar" for staff-written articles,[14] although contributing news feeds such as Reuters may use Lidar.[15]
General description
Lidar uses ultraviolet, visible, or near infrared light to image objects. It can target a wide range of materials, including non-metallic objects, rocks, rain, chemical compounds, aerosols, clouds and even single molecules.[4] A narrow laser beam can map physical features with very high resolutions; for example, an aircraft can map terrain at 30-centimetre (12 in) resolution or better.[16]
