Lidar is an acronym for light detection and ranging. The term lidar was originally a portmanteau of light and radar, but radar technology has evolved beyond the simple pulse that defines it, and “radar” is now generally used as an umbrella term that includes any electromagnetic wave-based sensor system. Scientists and engineers at NIST have been researching lidars since 1944. In fact, they developed one of the first lidars during World War II to detect enemy aircraft from their ground-based lasers so they could jam them.
The following sections describe what a lidar does as well as how it works:
What a Lidar Does
A lidar can scan across large areas in order to collect information about what it encounters. A lidar system typically comprises three major components:
1. A scanning device, which sweeps a laser beam across the target area to be mapped.
2. The receiver, which detects the reflection of the scattered light from the surface or objects in the scanned area and converts it to an electrical signal.
3. A processor that analyzes this information and creates a digital map of the scanned area according to the location of reflective surfaces detected by the lidar’s receiver.
How a Lidar Works
Lidars are similar to radars in that they emit energy pulses that are then reflected back into space by reflective surfaces such as buildings, cars, aircraft or birds present in their path of travel. It is also similar to radar in that the time required for the pulse to travel to a target and back is used to determine its distance from the lidar.
A lidar’s light source emits pulses of laser light in a specific direction—where it points depends on where you want to collect data. A spinning mirror directs these pulses out into space in a narrow beam, much like sweeping beams of flashlight across an area or bouncing them off walls.
Some lidars are tuned for vertical scanning, while others emit their energy horizontally so they can scan roofs or roadways with one device. For example, lidars have been used to produce precise three-dimensional maps of buildings by measuring reflected light from surfaces at several hundred locations, enabling construction crews to easily see any changes to the planned construction.
A lidar’s receiver measures the amount of light returned from each pulse and creates a range profile—an analog signal that shows distance versus intensity. A computer interprets these profiles to build a three-dimensional representation of the scanned area, such as an aerial map or point cloud.
For example, when you use lidar for 3D mapping in Google Maps’ Street View feature, the vehicles equipped with this technology capture millions of data points with their roof-mounted sensors every second they are on the road. The lidars generate more than 25 million discrete data points for each mile traveled by shooting lasers at reflective surfaces around them. An onboard processor quickly digitizes this information it can be viewed wirelessly on a laptop or smartphone.
Lidars can help make a city smarter by enabling drones to avoid collisions, cars to detect pedestrians and blind spots, and construction crews to easily see any changes made during the course of their work.
