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Lidar

Lidar is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Lidar rather than just read about it. In short: Lidar (, an acronym of light detection and ranging or laser imaging, detection, and ranging, often stylized LiDAR) is a method for determining ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the optical receiver. Lidar may operate in a fixed direction (e.g., vertical) or it may scan directions, in a special combination of 3D scanning and laser scann…

Lidar — main illustration
Lidar — illustration

Key takeaways

  • Lidar belongs to engineering; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Lidar to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Lidar from memory before moving on to harder problems.

Reference excerpt

Lidar (, an acronym of light detection and ranging or laser imaging, detection, and ranging, often stylized LiDAR) is a method for determining ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the optical receiver. Lidar may operate in a fixed direction (e.g., vertical) or it may scan directions, in a special combination of 3D scanning and laser scanning.

LiDAR is used within terrestrial, airborne, and mobile equipment around the globe. It is commonly used to make high-resolution maps, with applications in surveying, geodesy, geomatics, archaeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics, laser guidance, airborne laser swathe mapping (ALSM), and laser altimetry. It is used to make digital 3-D representations of areas on the Earth's surface and ocean bottom of the intertidal and near coastal zone by varying the wavelength of light. It has also been increasingly used in control and navigation for autonomous cars and for the helicopter Ingenuity on its record-setting flights over the terrain of Mars. Lidar has since been used extensively for atmospheric research and meteorology. Lidar instruments fitted to aircraft and satellites carry out surveying and mapping – a recent example being the U.S. Geological Survey Experimental Advanced Airborne Research Lidar. NASA has identified lidar as a key technology for enabling autonomous precision safe landing of future robotic and crewed lunar-landing vehicles.

History and etymology The essential concept of lidar was originated by E. H. Synge in 1930, who envisaged the use of powerful searchlights to probe the atmosphere. Under the direction of Malcolm Stitch, the Hughes Aircraft Company introduced the first lidar-like system in 1961, 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", 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 11 km and an accuracy of 4.5 m, to be used for military targeting. The first mention of lidar as a stand-alone word in 1963 suggests that 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) ..." The name "photonic radar" is sometimes used to mean visible-spectrum range finding like lidar. Lidar's first applications were in meteorology, for which the National Center for Atmospheric Research used it to measure clouds and pollution. 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; the New York Times predominantly uses "lidar" for staff-written articles, although contributing news feeds such as Reuters may use Lidar.

Theory

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. 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. Wavelengths vary to suit the target: from about 10 micrometers (infrared) to approximately 250 nanometers (ultraviolet). Typically, light is reflected via backscattering, as opposed to pure reflection one might find with a mirror. Different types of scattering are used for different lidar applications: most commonly Rayleigh scattering, Mie scattering, Raman scattering, and fluorescence. Suitable combinations of wavelengths can allow remote mapping of atmospheric contents by identifying wavelength-dependent changes in the intensity of the returned signal. The name "photonic radar" is sometimes used to mean visible-spectrum range finding like lidar, although photonic radar more strictly refers to radio-frequency range finding using photonics components. A lidar determines the distance of an object or a surface with the formula:

d = c ⋅ t 2 {\displaystyle d={\frac {c\cdot t}{2}}}

… excerpt ends here. Continue reading the full article.

Illustrations

Lidar: Lidar-derived image of the Marching Bears Mound Group, Effigy Mounds National Monument, United States
Lidar-derived image of the Marching Bears Mound Group, Effigy Mounds National Monument, United States
Lidar: A frequency addition source of optical radiation (FASOR) used at the Starfire Optical Range for lidar and laser guide star experiments is tuned to the sodium D2a line and used to excite sodium atoms in the upper atmosphere.
A frequency addition source of optical radiation (FASOR) used at the Starfire Optical Range for lidar and laser guide star experiments is tuned to the sodium D2a line and used to excite sodium atoms in the upper atmosphere.
Lidar: This lidar may be used to scan buildings, rock formations, et cetera, to produce a 3D model. The lidar can aim its laser beam in a wide range: its head rotates horizontally; a mirror tilts vertically. The laser beam is used to measure the distance to the first object on its path.
This lidar may be used to scan buildings, rock formations, et cetera, to produce a 3D model. The lidar can aim its laser beam in a wide range: its head rotates horizontally; a mirror tilts vertically. The laser beam is used to measure the distance to the first object on its path.
Lidar: Basic time-of-flight principles applied to laser range-finding
Basic time-of-flight principles applied to laser range-finding
Lidar: A basic lidar system involves a laser range finder reflected by a rotating mirror (top). The laser is scanned around the scene being digitized, in one or two dimensions (middle), gathering distance measurements at specified angle intervals (bottom).
A basic lidar system involves a laser range finder reflected by a rotating mirror (top). The laser is scanned around the scene being digitized, in one or two dimensions (middle), gathering distance measurements at specified angle intervals (bottom).

Worked examples

Example 1 — a first encounter with Lidar

Start with the simplest possible case. Write down what Lidar claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lidar before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lidar ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lidar

In research
Lidar appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Lidar in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Lidar is common in secondary-school and first-year university syllabi. It links to neighbouring topics Lidar, Meteorological instrumentation and equipment, Robotic sensing, so understanding it makes those chapters shorter.
In everyday life
Look for Lidar outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Lidar in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Lidar means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Lidar out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lidar in simple terms?

Lidar (, an acronym of light detection and ranging or laser imaging, detection, and ranging, often stylized LiDAR) is a method for determining ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the optical receiver. Lidar may operate…

Why does Lidar matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lidar?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lidar.

Tags

  • Lidar
  • Meteorological instrumentation and equipment
  • Robotic sensing
  • Sensors

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