On-board CME detection algorithm for the Solar Orbiter-METIS coronagraph

The METIS coronagraph is one of the instruments part of the payload of the ESA – Solar Orbiter mission to be launched in 2017. The spacecraft will operate much like a planetary encounter mission, with the main scientific activity taking place with the remote-sensing instruments during three 10-days intervals per orbit: optimization of the different instrument observing modes will be crucial. One of the key scientific targets of METIS will be the study of transient ejections of mass through the solar corona (Coronal Mass Ejections – CMEs) and their heliospheric evolution. METIS will provide for the first time imaging of CMEs in two different wavelengths: VL (visible light 580- 640 nm) and UV (Lyman-α line of HI at 121.6 nm). The detection of transient phenomena shall be managed directly by the METIS Processing and Power Unit (MPPU) by means of both external triggers (“flags”) coming from other Solar Orbiter instruments, and internal “flags” produced directly by the METIS on-board software. METIS on-board algorithm for the automatic detection of CMEs will be based on running differences between consecutive images re-binned to very low resolution and thresholded for significant changes over a minimum value. Given the small relative variation of white light intensity during CMEs, the algorithm will take advantage of VL images acquired with different polarization angles to maximize the detection capability: possible false detections should be automatically managed by the algorithm. The algorithm will be able to provide the CME first detection time, latitudinal direction of propagation on the plane of the sky (within 45 degrees), a binary flag indicating whether a "halo CME" has been detected.