Neutral Composition Information in ICON EUV Dayglow Observations

Since the earliest space-based observations of Earth's atmosphere, ultraviolet (UV) airglow has proven a useful resource for remote sensing of the ionosphere and thermosphere. The NASA Ionospheric Connection Explorer (ICON) spacecraft, whose mission is to explore the connections between ionosphere and thermosphere utilizes UV airglow in the typical way: an extreme-UV (EUV) spectrometer uses dayglow between 54 and 88 nm to measure the density of O⁺, and a far-UV spectrograph uses the O 135.6 nm doublet and N₂ Lyman-Birge-Hopfield band dayglow to measure the column ratio of O to N₂ in the upper thermosphere. Two EUV emission features, O⁺ 61.6 and 83.4 nm, are used for the O⁺ retrieval; however, many other features are captured along the EUV instrument's spectral dimension. In this study, we examine the other dayglow features observed by ICON EUV and demonstrate that it measures a nitrogen feature around 87.8 nm which can be used to observe the neutral thermosphere.