A weighted FBP reconstruction for plasmasphere CT imaging

This paper proposes a new topic on tomographic algorithms for volume reconstructing the density of the plasmasphere from a set of emission Extreme Ultraviolet (EUV) radiation. The plasmasphere is a torus region in the Earth’s magnetosphere that consists of cold dense plasma. Approximately 20% of the plasmasphere’s plasma particles are He⁺. Under the solar radiation, He⁺ resonantly scatters the 30.4 nm radiation (EUV). The fundamentals of this EUV tomographic imaging are similar to SPECT or PET. However, the Earth completely absorbs all the EUV photons passing through it. The traditional CT reconstruction algorithms can not be used in this kind of imaging case. This paper introduces the fundamentals to use the CT methods to image plasmasphere density. A mathematical plasmasphere model is defined for EUV imaging. We propose tow data sufficiency conditions for parallel-beam and fan-beam reconstructions from EUV projections, respectively. Both parallel-beam and fan-beam algorithms are derived to reconstruct plasmasphere density from these EUV radiation projections. The key idea is to remove the complete absorption effect of the Earth with a specific weighting function. Computer-simulation studies are presented to verify our formulas.