Headlights That See Through a Downpour by Tracking and Hiding Raindrops

"Seeing" Through Raindrops
Srinivasa G. Narasimhan and Carnegie Mellon University via Technology Review

Researchers at Carnegie Mellon University have figured out how to thwart the weather when you're behind the wheel by looking straight through the rain drops or snow that create that white-out effect when headlights meet heavy precipitation at night. By detecting and tracking individual rain droplets or snow as they fall through a car's headlight beams, they've created a system that can "dis-illuminate" them by adjusting the headlight beams to only shine around them rather than on them.

The system works out to roughly 13 feet in front of the headlights, the range in which heavy snow or rain reflecting headlights can obscure a driver's vision. A digital projector illuminates incoming raindrops for a few milliseconds, long enough for a camera mounted on the side of the projector to capture their positions and trajectories. Software then calculates exactly where those raindrops are headed and sends a signal to the headlights, which adjust so that the light rays that would hit that raindrop are switched off.

In other words, in the middle of a downpour (and while moving) the system tracks raindrops in realtime and adjusts light rays just as quickly as those raindrops can fall. The system isn't perfect--in heavy rain accuracy is at 70 percent (that is, it removes 70 percent of the rain from view) at roughly 18 miles per hour. At 60 miles per hour, that drops to just 15 or 20 percent. But even 20 percent is a fairly good bump in visibility--certainly better than zero percent. The next step is to make the the system better at accounting for car movements that aren't simply straight forward (presumably compensating for turning or lane changes and the like).