Thermospheric Density Profiles from EUV Airglow

The middle thermosphere represents the largest observational gap in neutral densities between Earth's surface and exosphere, as evidenced by the fact that no observations in this region are used to estimate the MSIS 2.0 parameters. New observations of this region are needed to contribute to modeling and assimilation efforts as the characterization of near-Earth space grows in importance. Thermospheric O and N2 are often observed using far-UV dayglow at 135.6 nm and in the N2 LBH bands; however, these observations suffer from ionospheric contamination via radiative recombination and from poorly modeled electron precipitation. In this work, we detail the formulation and validation of thermospheric O and N2 density measurements at 150-400 km altitude derived from extreme-UV dayglow (EUV) at 61.6 nm and 87.8 nm measured by the Ionospheric Connection Explorer (ICON). These bands are not believed to suffer from contamination by the ionosphere or by conjugate photoelectrons and auroral electrons, and thus these methods could eventually be used for observations of the thermosphere in regions previously unobserved.