What Is Lidar?
Lidar technology can create accurate topographic maps.
CREDIT: U.S. Geologic Survey
Whether you need to map out a landscape or discover an ancient city, lidar — an advanced application of laser technology — is probably your best bet.
Recently, a global team of researchers using lidar technology discovered the lost city of Mahendraparvata underneath the temples of Angkor Wat in Cambodia. The unobtrusive scanning method allowed researchers to unearth an entire network of streets and city blocks without harming the priceless structures above.
Although lidar uses sophisticated technology, there's nothing mysterious about how it works, or why it presents so many opportunities for researchers of all stripes.
What is lidar?
Lidar is an acronym that stands for "light detection and ranging," although its name may originate from a combination of "light" and "radar." A lidar device is usually attached to an airplane or helicopter, and then flown above an area that scientists wish to study.
A lidar device sends out pulses of laser light over an area of interest, while a scanner and a GPS receiver interpret the data and assemble it into a detailed 3D map. The targeted area reflects the light, and depending on how long it takes, the scanner and the receiver can calculate the shape and elevation of the target.
What is the difference between lidar and radar?
Although lidar and radar have similar names, the two scanning methods function in very different ways.
Radar ("radio detection and ranging") devices broadcast radio waves to bounce off of objects. When a radar dish or antenna receives "pings" from distant bodies, it can calculate an object's distance, size and rough trajectory with fair accuracy.
The wavelengths in radar scanning are much longer than those in lidar. This means that radar scans do not need a particular target, and can sweep a wide area over a very short amount of time. As a practical example, a policeman could set up a radar system to determine which cars are speeding, or use a lidar device to determine if a car in question is speeding.
What is lidar used for?
Lidar's primary function is for scanning and mapping either geographic regions or man-made objects. When creating topographic maps, lidar uses infrared light over land, and visible green light to penetrate water and depict seafloors.
As with the city of Mahendraparvata, archaeologists can use lidar to scan beneath vegetation, and even existing structures, to see long-standing features that have been covered by plants or erosion. Alternatively, if plants are of interest, lidar can create forest maps accurate enough to estimate an entire ecosystem's biomass.
Aiming lidars skyward can help meteorologists determine the weather and astrophysicists detect minerals on the surface of foreign planets, like Mars, through lidar tech in rovers and landers. Robotic vehicles and other autonomous devices use lidar to navigate, while architects and engineers can scan structures with lidar in order to recreate them or examine their stresses under real-world conditions. [See also: 10 Technologies Poised to Transform our World]
Who invented lidar?
Lidar does not have one specific inventor. It came into being in the early 1960s in the United States, alongside the widespread use of lasers in military applications. The National Center for Atmospheric Research used it to research weather patterns in clouds. As the technology became cheaper and more widely available, industries from farming to law enforcement adopted it.
How accurate is lidar?
The accuracy of lidar depends on a number of factors, including scanning distance and the brand of scanner used. According to Airborne 1, one of the foremost lidar mapping outfits in the United States, lidar scanners that attach to airplanes or helicopters can generally scan with an accuracy of about 2 centimeters (0.79 inches) at an elevation of 4,000 feet (1,219 meters). At this elevation, a lidar device can generally scan an area in intervals of 4.5 feet (1.4 m). Favorable flying conditions and more advanced GPS models can improve these numbers, while obstructions and old equipment can hinder its accuracy.
Lidar is one of the most versatile technologies available, and with any luck, it hasn't uncovered its last lost city.