Characterization of the Daytime Ionosphere with ICON EUV Airglow Limb Profiles

The NASA Ionospheric Connection Explorer Extreme Ultraviolet spectrograph, ICON EUV, images one-dimensional altitude profiles of the daytime extreme-ultraviolet (EUV) airglow between 54-88 nm. This spectral range contains several OII emission features derived from the photoionization of atomic oxygen by solar EUV. The primary target of the ICON EUV is the bright OII (P-4 - S-4) triplet emission spanning 83.2-83.4 nm that is used in combination with a dimmer but complementary feature (P-2 - D-2) spanning 61.6-61.7 nm that are jointly analyzed with an algorithm that uses discrete inverse theory to optimize a forward model of these emissions to infer the best-fit solution of ionospheric O+ density profile between 150-450 km. From this result, the daytime ionospheric F-region peak electron density and height, NmF2 and hmF2 respectively, are inferred. The science goals of ICON require these measurements be made in the regions of interest with a vertical resolution in hmF2 of 20 km and a 20% precision in NmF2 within a 60-second integration corresponding to a 500 km sampling along the orbit track. This paper describes the results from the ICON EUV over the first year of the mission, which occurred primarily under solar minimum conditions. It describes adjustments made to the algorithm to improve not only the quality of data products during this time, but also to improve speed and performance while simultaneously meeting the ICON measurement requirements. It also provides examples of results and an overview of key features and limitations to consider when using these products for scientific studies.