Camera Images Aurora Hyperspectrally

The first-ever hyperspectral pictures of the aurora borealis, or northern lights, revealed a previously unknown atmospheric phenomenon.

The Norusca II hyperspectral camera was tested in late January at the Kjell Henriksen Observatory, where it imaged a major solar flare that jettisoned a burst of high-energy particles known as a coronal mass ejection (CME). This new phenomenon produced magnificent auroras—nature’s celestial fireworks—when it eventually slammed into the Earth’s magnetic field.

“Our new all-sky camera opens up new frontiers of discovery and will help in the detection of auroras and the understanding of how our sun impacts the atmosphere here on Earth,” said Fred Sigernes of the University Center in Svalbard.

The aurora as seen as a color composite image from the Norusca II camera. Three bands were combined to make the image. Each band was assigned a different color — red, green and blue — to enhance the features of the aurora for analysis. The research from the University Center in Svalbard could help scientists to better understand how the sun impacts the Earth’s atmosphere. Courtesy of Optics Express.

The space-weather researchers imaged the aurora with unprecedented clarity through a layer of low-altitude clouds, which would have thwarted earlier-generation instruments. The camera also revealed something unexpected: a very faint wave pattern of unknown origin in the lower atmosphere. The wave pattern resembles “airglow” — the natural emission of light by Earth’s atmosphere. Airglow can be produced by a variety of known sources, including chemical reactions and cosmic rays striking the upper atmosphere.

“After the January CME, we think we saw an auroral-generated wave interaction with airglow,” Sigernes said. This would be an entirely new phenomenon and, if confirmed, would be the first time airglow has been associated with auroras.

“Additional development and commissioning will also hopefully verify our intriguing first results,” he said.

The red arrow points to the unidentified low-intensity wave pattern, which the researchers suspect is an auroral-generated wave interaction with airglow. For contrast, the blue arrow points to the faint emission of the Milky Way. Courtesy of Optics Express.

Current cameras used to study such atmospheric phenomena collect all the light together into one image; they lack the ability to separately capture and analyze multiple slivers of the visible spectrum. This means that researchers wanting to study specific bands or small portions of an aurora’s spectrum would have to use a series of filters to block out the unwanted wavelengths.

The Norusca II can achieve the same result without any moving parts, using its advanced optics to switch among all of its 41 separate optical bands in a matter of microseconds — orders of magnitude faster than an ordinary camera. This opens up new possibilities for discovery by combining specific bands of the same ethereal phenomenon into one image, revealing previously hidden details. This form of multispectral imaging also will enable scientists to better classify auroras from background sky emissions and study the way they cluster in the atmosphere.

Students perform measurements of the aurora in front of the Kjell Henriksen Observatory in Svalbard, Norway, November 2010. Courtesy of Njaal Gulbarndsen.

“A standard filter wheel camera that typically uses six interference filters will not be able to spin the wheel fast enough compared to the Norusca II camera,” Sigernes said. “This makes the new hyperspectral capability particularly useful for spectroscopy, because it can detect specific atmospheric constituents by their unique fingerprint, or wavelengths, in the light they emit.”

Details on the camera and results of its first images were published in the open-access journal Optics Express.

For more information, visit: www.unis.no