You're driving down a twisting mountain road at night and all of a sudden the storm clouds open. Whatever you do with your headlights you can barely see more than a couple of feet. Fortunately, that's all set to change thanks to a team of scientists who can make the reflections from the rain disappear.
The researchers, from Carnegie Mellon University, have developed a system that can detect the distinctive streaks left by raindrops and snowflakes, and remove them by changing the way the headlights illuminate the path ahead of the vehicle.
To do that, their system uses a digital projector to illuminate the raindrops for a couple of milliseconds, then works out what their likely path is within the drivers field of view. Armed with that information, it's possible to selectively switch off beams of light from the headlights that would illuminate the drops as they fall—achievable when you have a matrix of lights which can be switched on and off rapidly to steer beams.
While that means that there is less light projected from the headlights, it also means that there is far less glare as the drops don't reflect back any of the light. Combined, the result is much improved visibility. While the system's been tested in the lab, it's also been used in a Toyota Prius and can effectively remove rain streaks up to four meters in front of the car—the so called "critical range" at which glare is most distracting.
The only snag is that the system doesn't currently cope too well at high speeds. While it can remove 70 per cent of streaks at 18mph, that drops to 15 to 20 per cent at 62mph—and it's not clear how that can be improved without some serious expense. [Technology Review, Carnegie Mellon]
Image by Chrisbkes under Creative Commons license and Carnegie Mellon