LiDAR: Light Detection And Ranging

Elizabeth Borneman

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LiDAR is an acronym for ‘light’ and ‘radar,’ a tool developed to detect targets and to use reflected light off of objects as a kind of visual sonar. LiDAR systems can be outfitted on to planes, helicopters, drones, and other elevated platforms.

Light Detection And Ranging (LiDAR) can determine how far objects are away from each other by shining a laser onto a target and analyzing the light that bounces back.

The laser light pulses returns high resolution three-dimensional geographic coordinates (latitude, longitude, and height) of each point in the LiDAR point cloud data. LiDAR samples the surface of the Earth to return information about the depth and height of features.

LiDAR Pulse and Returns

A pulse of light is beamed down from the LiDAR system to the Earth’s surface and the return pulses contain information about the location and distance from that feature to the LiDAR system. Different return pulses can provide information about the geographical landscape depending on the order in which those pulses get returned.

The first return is measured as the highest point in the landscape. This may be the top of a building, the top of vegetation such as a tree canopy, or a mountain top. The last return is recorded as the lowest point in a landscape such as the ground.

An image of a plane with a LiDAR system sending light pulses to collect dat about a forest.
Pulses emitted by a LiDAR system are bounced back to the system in order to collect information about the height of features. Image: Jason Stoker, USGS, public domain.

Types of LiDAR Data

Two types of LiDAR are topographic and bathymetric data. Topography data collected with topographic LiDAR can then be interpolated to create digital elevation models (DEM).

Bathymetric lidar measures seafloor and riverbed elevations using water-penetrating green light.

LiDAR systems are used to create incredibly detailed maps and data that assist researchers in the fields of geography, archeology, geology, seismology, atmospheric sciences, laser studies, and much more.

When Was LIDAR First Developed?

LiDAR’s first applied use was in the 1960s and came soon after the invention of lasers. A LiDAR instrument is made up of three parts: a laser, a scanner, and a specialized GPS receiver.

Used in combination with radar, LiDAR was originally used in atmospheric studies to measure clouds by the National Center for Atmospheric Research.

Mapping the Surface of the Moon with LiDAR

LiDAR later became more publically known when the Apollo 15 mission used it to map the surface of the moon more accurately than ever before.

LiDAR – High Resolution Data

The technical aspects of LiDAR are many. LiDAR uses UV light and light close to infrared on the spectrum to beam light pulses that target certain objects and analyze their distances based on the refraction of light that is bounced back.

Scientists and mapping experts can use LiDAR to analyze both natural and man-made geographical features with accuracy, precision, and flexibility.

The theory is that objects of varying shapes, sizes, densities and distances will reflect light back at different speeds and thus create a high-resolution map of the surroundings.

LiDAR was used to Map Flooding from Hurricane Isaac. Source: USGS
LiDAR was used to Map Flooding from Hurricane Isaac. Source: USGS

Like Apollo 15 and the work done by atmospheric scientists to map the upper atmospheres, LiDAR is continuing to be instrumental technology in the future of space missions to planets like Mars, both for manned and unmanned missions. LiDAR technology can map surfaces of planets mankind can’t reach by space rovers (yet) and be integral for finding proper landing spaces for space vehicles in the future.

Basic Components of LiDAR

Most LiDAR is made up of the same basic components- the laser, a scanner and optics, photodetectors and receiver electronics, as well as position and navigation systems. The laser is generally eye-safe (meaning the laser isn’t strong enough to damage a human eye) except for very strong lasers used by atmospheric scientists to penetrate the highest reaches of the atmosphere.

Top image is an aerial photo of a road and a hill.  The bottom image is a topography surface of the same area.
Top: Aerial image of US Highway 191 north of West Yellowstone, Montana. Bottom:   LiDAR imagery shows the road passing through a landslide deposit. Brown and white are found at higher elevations, while green is found at lower levels.  Shading denotes steeper slopes. The landslide may be visible in the aerial photo with a trained eye, but it is more visible in the LiDAR. Images: Yellowstone Volcano Observatory (YVO), USGS, public domain.

The scanner, depending on its speed, develops images faster or slower depending on the quality and can scan a specific area. The optics of a LiDAR mechanism is developed to return a clear picture of what the laser and scanner have detected. Sensitive photodetectors are used to create a physical picture of the objects that have been scanned, all of which is mounted on platforms based on their use (i.e. airplanes, satellites, rovers, etc.). LiDAR can print in 2D or 3D.

Many Use of LiDAR

LiDAR has many other practical applications including mapping crop yields in agriculture, mapping terrestrial and extraterrestrial bodies, studying the atmosphere and contributing to military technology. LiDAR is also used to detect objects underground and is vitally important for archeologists.

LiDAR data can find previously unmapped or unknown fault lines contributing to localized earthquakes as well as faults in building structures.

References

USGS. 2014. Light Detection and Ranging. Web access 5 January, 2015. https://lta.cr.usgs.gov/LIDAR

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About the author
Elizabeth Borneman
My name is Elizabeth Borneman and I am a freelance writer, reader, and coffee drinker. I live on a small island in Alaska, which gives me plenty of time to fish, hike, kayak, and be inspired by nature. I enjoy writing about the natural world and find lots of ways to flex my creative muscles on the beach, in the forest, or down at the local coffee shop.

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