Cameras capture aurora’s altitude

Caren B. Les, caren.les@photonics.com

Humans have long looked at the aurora borealis as a phenomenon of beauty and mystery, but some also look to those northern lights as a source of scientific information.

The aurora could give us important hints about how the Earth is connected to space, said Ryuho Kataoka, associate professor at the National Institute of Polar Research in Tokyo.

In 2010, Kataoka and collaborators headed to Alaska to begin a three-winter study of the aurora borealis. Their remotely controlled stereoscopic setup included two low-cost DSLR (digital single-lens reflex) cameras, placed 8 km apart. The cameras captured simultaneous all-sky images that were then combined to create a 3-D photograph of the aurora.

The researchers equipped each camera with a fish-eye lens to capture a very wide field of view, maximizing the overlapping regions of the two cameras. They also used GPS units to accurately find the overlapping emission patterns.

Subtle differences between the left and right images allow researchers to measure the altitude where electrons in the atmosphere emit the light that produces an aurora. Photo courtesy of Ryuho Kataoka et al, 2013

Using the parallax of these emission patterns, the group measured the emission altitude of the northern lights, or the altitude where electrons in the atmosphere emit the light that produces the aurora, Kataoka said. Parallax is defined as the difference in the apparent position of an object when observed at different angles.

“From the emission altitude of an aurora, we can calculate back the energy of electrons precipitating from space,” he said. The principle, he explained, is that more energetic electrons can penetrate into denser atmosphere – that is, lower altitudes.

It was the cameras’ spatial resolution that enabled the group to obtain aurora emission altitudes on such a fine scale for the first time, Kataoka said, adding that the number of pixels in DSLR images is more than an order of magnitude greater than that of typical scientific-grade CCD cameras.

The dynamics of the small-scale features of the aurora are still not well understood, Kataoka said. “We would like to find unexpected [or] unknown time variations of localized emissions of the northern lights. For example, if we find something like very low altitude transient spots, it would reflect the fundamental spatial scale and temporal scale of a very energetic process working in the northern lights.”

The research appears in Annales Geophysicae (doi: 10.5194/angeo-31-1543-2013).