Digital cameras used to measure height of Northern Lights

Scientists have used two digital single-lens reflex (SLR) cameras set 8 km apart to capture 3D images of Northern Lights and determine the exact height of the phenomenon.
Ryuho Kataoka from the National Institute of Polar Research in Tokyo, Japan, and colleagues, used the cameras to determine the altitude where electrons in the atmosphere emit the light that produces aurora.
While scientists have obtained altitude maps of aurora before, this is the first time the emission height of Northern Lights has been measured using images captured with digital SLR cameras.
Kataoka came up with the idea of using cameras to measure the height of Northern Lights or aurora borealis after working on a 3D movie for a planetarium.

"We had initial success when we projected the digital SLR images at a planetarium and showed that the aurora could be seen in 3D. It was very beautiful, and I became confident that it should be possible to calculate the emission altitude using these images," said Kataoka, who also works at the Graduate University for Advanced Studies (Sokendai) in Hayama, Japan.
He teamed up with other Japanese researchers and an American scientist to do it.

The separation distance between the human eyes is what allows us to see in 3D. When we look at an object, the images captured by the left and right eyes are slightly different from each other and when combined they give the brain the perception of depth.

But because the distance between our eyes - about 5 cm - is small, this only works for objects that are not very far away.
Since aurora extend between about 90 and 400 km in altitude, a much larger separation distance is needed to see them in 3D.
The researchers used two cameras, mimicking the left and right eyes, separated by 8 km across the Chatanika area in Alaska.
Their two digital SLRs, equipped with fisheye lenses and GPS units, captured two simultaneous all-sky images that the researchers combined to create a 3D photograph of the aurora and measure the emission altitude.

"Using the parallax of the left-eye and the right-eye images, we can calculate the distance to the aurora using a [triangulation] method that is similar to the way the human brain comprehends the distance to an object," said Kataoka.
Parallax is the disparity in the perceptible position of an object when seen at different angles.
The new technique is low cost and allows researchers to measure the altitude of small-scale features in the aurora. Further, it opens up the door for citizen scientists to get involved with auroral research.
The results are published in Annales Geophysicae, a journal of the European Geosciences Union (EGU).