Ubiquitous adoption of lidar in self driving cars needs one major thing: lower cost. Lidar has proven to be a capable technology for level 4 autonomous driving, and is already used in self driving taxis by Waymo and Cruise. But the spinning lidar domes on top of these cars cost thousands of dollars, and that number needs to drop by at least an order of magnitude. In this post from Vik’s Newsletter Vik provides a valuable introduction to automotive lidar technology and its challenges.
There are over 140 startups in the lidar space looking to make that happen and more.
Lidar for Autonomous Vehicles
Lidar stands for Light Detection and Ranging and is a method where infrared laser light is used to measure the distance to a remote object. This technology is not new. For years, it has been used for imaging vegetation, urban terrain, hidden archeological sites, building construction and recently, in augmented reality. Its particular superpower is that it can generate high resolution images of its surroundings much better than radar can. While lidar and radar are fundamentally similar in operation, the use of shorter wavelengths (lasers) compared to radar (microwaves) gives it the ability to generate highly detailed images.
In last week’s article, we looked at the camera versus lidar debate for self driving cars. If you missed that, you can read it below.
Since 2020, lidar has become especially relevant as the “eyes” of autonomous vehicles. Its ability to rapidly generate precise 3D images of the surroundings is critical in making accurate distance estimations for self driving. The downside of lidar is cost. Laser sources, detectors and associated electronics and mechanics are expensive. The rise of solid-state lidar technologies may still offer a competitive price point for widespread adoption of lidar in self driving cars.
The next sections will explain the inner workings of lidar technology.
Wavelength of Operation
Lidar systems are predominantly designed to operate in one of two wavelengths that are in the infrared region (750 nanometers to 15 micrometers) of the electromagnetic spectrum, but outside visible range (380 to 700 nanometers).
905 nm (near infrared, or NIR)
1550 nm (short wave infrared, or SWIR)
The choice of wavelength in a lidar system depends on the output power of laser sources, sensitivity of detectors and the interference from natural and artificial light sources in the same spectrum.
Sunlight is one of the dominant sources of interference which has a lot of energy in the infrared region of the spectrum. A measure of sunlight’s impact is called the solar photon flux, which is the amount of sunlight hitting the earth at any given wavelength.
There are some noticeable dips at 905, 940 and 1550 nm due to absorption by water vapor in the upper atmosphere, which conveniently reduces interference in systems at ground level. Unfortunately, the same effect absorbs radiation in foggy and rainy road conditions. The proximity of the 905 nm wavelength to the visible range causes two other concerns:
905 nm laser wavelengths are easily absorbed by the retina causing damage from prolonged exposure. As a result, there are strict standards for lidar eye safety that must be adhered to.
There are plenty of interference sources near visible light, both from the sun and from vehicle headlamps that degrade the system performance.
However, at shorter wavelengths, photodetectors are generally more sensitive and laser sources are more powerful and inexpensive. Ouster, for example, has actually adopted 850 nm for its lidar technology despite high solar photon flux due to better visibility in damp conditions, improved source and detector performance, with patented approaches to rejecting environmental interference.
For the complete introduction to automotive lidar CLICK HERE.
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