[P-EM12] Coupling Processes in the Atmosphere-Ionosphere System

[PEM12-P35] Reconstruction of ionospheric oxygen ion density distribution from ISS-IMAP/EUVI data

*中野 慎也^1,2,3、穂積 裕太^4,5、齊藤 昭則⁶、吉川 一朗⁷、山崎 敦⁸、吉岡 和夫⁷、村上 豪⁸ (1.情報・システム研究機構　統計数理研究所、2.情報・システム研究機構　データサイエンス共同利用基盤施設、3.総合研究大学院大学、4.Catholic University of America、5.NASA Goddard Space Flight Center、6.京都大学大学院理学研究科、7.東京大学大学院新領域創成科学研究科、8.JAXA 宇宙科学研究所)

キーワード：極端紫外光トモグラフィ、酸素イオン、ポアソンノイズ、F層

We have developed a method for reconstructing the oxygen ion density distribution in the nightside ionosphere from EUV images taken by the EUVI-B imager of ISS-IMAP. The EUVI-B imager mainly observed the 91.1 nm emission from the recombination of O+ ions and electrons. Assuming that the electron density is equal to the O+ density in the F-region where the imager observes, the EUV intensity observed by EUVI-B is approximately proportional to the line-of-sight integral of the square of the O+ density. This enables us to estimate the O+ density distribution in the F-region from a sequence of EUVI-B data in each International Space Station (ISS) orbit. We represent the square of the O+ density with 2nd-order B-spline functions. The weights of the basis functions are then estimated to reconstruct the density distribution. To guarantee that the estimated density is non-negative, we convert each weight into a logarithm and the optimal value of the logarithm is obtained with a Bayesian approach. An estimate of the O+ distribution was obtained each orbital period of ISS, approximately every 90 minutes. It is demonstrated that the proposed method successfully reconstruct the O+ density distribution in the ionosphere.