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Image artifacts - Cosmic rays

Cosmic rays and solar energetic particles are highly energetic particles that travel through space. Some of these originate from the Sun. Others, known as galactic cosmic rays, come from outside the solar system. When they pass through the detectors, they produce thin bright spots or streaks.

cosmic ray
Close up of cosmic ray track seen on the STEREO Behind COR2 detector.

The high compression factors used for the temporary beacon images can cause cosmic ray events to be significantly distorted, as shown in the sample images below. Even the full resolution data have some compression applied to them, resulting in a small amount of distortion of the brightest cosmic rays.

Cosmic rays seen in beacon data   Cosmic rays seen in full resolution data
Two cosmic rays distorted by the high compression factors applied to beacon data, as seen by the STEREO Behind EUVI telescope on January 18, 2010   Same cosmic rays as seen in the full resolution data. Many more cosmic ray events are visible. Only the brightest two show up in the beacon image.

On July 19, 2011, the software for generating the browse images was changed to not apply smoothing when making JPEG images that are larger in size than the original data. The smoothing, as seen in the left image above, was found to contribute to making the cosmic ray features look like artificial structures. The unsmoothed images, although not quite as pleasing looking, are more representative of the actual data.

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Last Revised: Wednesday, 20-Jul-2011 13:34:54 EDT
Responsible NASA Official: [email address: therese.a.kucera<at>nasa<dot>gov]
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