Fully autonomous cars are edging closer to reality, driven by advanced sensors that can avoid a crash before it happens. Leading the charge in this area is LIDAR, a light sensing technology creates a 3-D map of a car’s surroundings using a laser and receiver. But how does it work?
If you’ve ever seen an autonomous vehicle you may have noticed a rapidly spinning tube mounted on its roof. This is a LIDAR unit. Its role is to measure the distance of objects relative to the position of the car in 3-D.
(LIDAR isn’t just used in self-driving cars. It’s also used extensively by aircraft to map large areas of inaccessible terrain in great detail, even detecting the shape of individual trees.)
First, a laser unit fires a short pulse of light. The pulse rebounds off a point such as the rear of the car in front and is detected by a sensor in the laser unit.
A computer connected to the unit measures the time between the initial pulse and the light return and, using the speed of light, calculates the distance the light has travelled.
This isn’t the full story, though. Knowing the distance between two objects is not just about measuring point-to-point distance, but also the angles of the LIDAR unit and on which the pulse was fired.
Roads aren’t completely smooth. When a car is on the move, it rocks side to side. So a laser pulse fired horizontally from the top of the car may not be horizontal to the road.
Taking this into account is vitally important when measuring a car’s surroundings. A slight angle change could mean the difference between two cars colliding or stopping in time because it changes light’s travel time between the two points.
Keeping track of these angle changes and feeding this data to the computer is the role of what’s called the Inertial Measurement Unit. It, the laser unit and computer track the distance of thousands of points each second around the entire vehicle. This helps to build a digital image that allows the car to ‘see’ what’s around it, and it works in pitch black.
Google’s LIDAR technology can see road works, parked cars and even hand signs from a cyclist. See it in action below.
Jake Port contributes to the Cosmos explainer series.
Read science facts, not fiction...
There’s never been a more important time to explain the facts, cherish evidence-based knowledge and to showcase the latest scientific, technological and engineering breakthroughs. Cosmos is published by The Royal Institution of Australia, a charity dedicated to connecting people with the world of science. Financial contributions, however big or small, help us provide access to trusted science information at a time when the world needs it most. Please support us by making a donation or purchasing a subscription today.