High-speed camera system catches close-ups of snowflakes in mid-air
By Ben Coxworth
April 10, 2013
Falling snow can play havoc with radar systems, so the more that we know about the manner in which snow falls, the better that those systems can be equipped to compensate for it. That’s why for the past three years, researchers from the University of Utah have been developing a device known as the Multi-Angle Snowflake Camera – or MASC. Using three cameras and two motion sensors, it captures 3D photos of snowflakes in free-fall.
The physical form of a snowflake has a marked effect on how it falls, and it turns out that the super-close-up photos of snowflakes that we’re used to seeing don’t depict what a typical snowflake looks like. According to associate professor of atmospheric sciences Tim Garrett, “These perfectly symmetric, six-sided snowflakes, while beautiful, are exceedingly rare.” They’re usually selected by hand, because their flat shape allows them to sit nicely on a microscope slide.
In reality, however, falling snowflakes accumulate water droplets that freeze onto them, they collide and meld with other snowflakes, and generally form into all sorts of oddball shapes. By photographing whatever passes in front of it in high-resolution 3D, the MASC provides a more accurate overview of what forms snowflakes typically take – it also measures the speed at which they fall past it.
The ring-shaped device is roughly one foot (30 cm) wide by four inches (10 cm) tall, and incorporates two 1.2-megapixel cameras and one 5-megapixel camera. When triggered by the top-mounted motion sensor, the three cameras all snap simultaneous images of the flake(s) falling through the ring, from three different angles. The lower motion sensor then detects when those same flakes exit the bottom of the ring, allowing their speed to be calculated.
The MASC cameras take their shots at an aperture of f/5.6 and shutter speeds of up to one 40,000th of a second. Tens of thousands of images can be recorded in one day, although all of the photos are black-and-white, as color filters block some of the light.
Garrett and mechanical engineer Cale Fallgatter are now commercially developing the system through their spin-off company, Fallgatter Technologies. NASA and the U.S. Army provided funding to develop the technology, while the snowflake observation trials were funded by the National Science Foundation.