Self-driving cars are developing apace and are ultimately expected to become safer than those driven by people, but first they will have to overcome their biggest nemesis: snow. It's slippery, unpredictable and obscures road markings. Ford has given some insight into how its autonomous cars will deal with the white stuff.

The main weapon in the autonomous car's arsenal against snow is the LiDAR sensor. LiDAR (or Light Detection And Ranging) is widely used by autonomous cars as a means of scanning the world around them to create a navigable 3D model.

Of course, for an area to be accurately mapped using LiDAR, it can't be covered in snow. Ford says that an area that is covered in snow, however, can be navigated if it has been mapped by LiDAR previously. An existing map of the road and surrounding infrastructure created when the weather was good can be used as a baseline to identify the car's position even when it is snowy.

According to Ford, the LiDAR sensors used by its autonomous cars are able to scan 2.8 million laser points a second and are so powerful that they can identify falling snowflakes and raindrops. While this allows them to create high-resolution 3D maps, it also means that snow or rain can be viewed as an obstacle by autonomous cars. In order to avoid this, Ford has developed an algorithm that identifies precipitation and filters it out of a car's "vision."

In addition to LiDAR sensors, Ford's autonomous vehicles use cameras and radar to map and monitor the environment around them. Using multiple different sensors allows the vehicles to build up a more detailed view of their environment, with the data collected combined in a process called "sensor fusion."

As well as providing what Ford calls "robust 360-degree situational awareness," sensor fusion allows for a degree of redundancy. In the event that one of a vehicle's sensors is covered by ice, snow, grime or debris, the vehicle can still operate using the data provided by the other sensors. Ford suggests that, in the future, autonomous vehicles may be able to clean or defog sensors themselves.

These approaches to scanning and modelling their environments are said to allow Ford's autonomous vehicles to locate themselves to within 1 cm (0.4 in), compared to over 30 ft (9.1 m) as is the case with GPS, the carmaker says. They do, however, produce and process over 600 GB of data every hour, which Ford says is more data than the average person uses in 10 years on their smartphone.

Ford carries out its winter weather road testing in Michigan, including at Mcity, and claims to be the first automaker to publicly demonstrate autonomous vehicle operation in the snow.

The video below provides an overview of some the technologies used by Ford's autonomous vehicles for navigating in the snow.

Source: Ford

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