Solar image analysis and visualization

Two STEREO spacecraft each carry a SECCHI instrument suite. Each suite includes one Extreme Ultra-Violet Imager (EUVI), two white-light coronagraphs (COR1 and COR2), and two wide-angle heliospheric imagers (HI1 and HI2). Detailed technical accounts of EUVI, COR1 and the HIs appear in separate published papers.

SECCHI images pose a visualization challenge on two fronts. Full frames are 2048 by 2048 pixels, except the HIs, which are usually binned 2 by 2 onboard, so most computer screens cannot show them at full size and full resolution. More significantly, the five instruments were built to follow a coronal mass ejection (CME) from its birth, seen by EUVI, through its travel across the heliosphere, seen by the HIs. A sequence tracing a CME from its starting point to Earth therefore mixes images of very different resolution, ranging from 1.7 arcseconds per pixel for EUVI to 2.15 arcminutes per pixel for HI2, a difference of roughly 75 times.

The apparent size of the ejections poses a similar problem. A CME grows by orders of magnitude as it expands through the heliosphere, so the angular scale of the object changes just as dramatically as the image resolution does.