A Technique for Removing Background Features in SECCHI--EUVI He II 304 A Filtergrams: Application to the Filament Eruption of 22 May 2008

TL;DR

This paper introduces a novel image processing technique that effectively removes background features from EUV He II 304 A images, enhancing the visibility of filament structures during eruptions, demonstrated on a 2008 event.

Contribution

The paper presents a new method for isolating filament structures in EUV images by subtracting geometrically aligned images from STEREO spacecraft, improving filament eruption analysis.

Findings

Successfully applied to the 22 May 2008 filament eruption

Enhanced visibility of filament dynamics in EUV images

Technique reduces background noise in STEREO observations

Abstract

The STEREO mission has been providing stereoscopic view of filament eruptions in EUV. The clearest view during a filament eruption is seen in He II 304 A observations. One of the main problems visualizing filament dynamics in He II 304 A is the strong background contrast due to surface features. We present a technique that removes background features and leaves behind only the filamentary structure, as seen by STEREO-A and B. The technique uses a pair of STEREO He II 304 A images observed simultaneously. The STEREO-B image is geometrically transformed to STEREO-A view so that the background images appear similar. Filaments being elevated structures, i.e., not lying on the same spherical surface as background features, do not appear similar in the transformed view. Thus, subtracting the two images cancels the background but leaves behind the filament structure. We apply this technique to study the dynamics of the filament eruption event of 22 May 2008, which was observed by STEREO and followed by several ground-based observatories participating in the Joint Observing Programme (JOP 178).