Remote sensing the Ionosphere using RAIDS: Comparisons of 83.4 nm airglow to ground-based ion density profiles

We present results which support that the Remote Atmospheric and Ionospheric Detection System (RAIDS) is able to identify changes in the daytime ionosphere via changes in the emission profile of the OII 83.4 nm airglow. As a sensor suite aboard the International Space Station, RAIDS is ideally placed to remotely sense these changes during solar minimum due to the lower altitude of the platform. The RAIDS EUV Spectrometer collects global measurements of the daytime O+ airglow at 83.4 nm. This emission feature originates in the lower thermosphere and then radiates into the ionosphere, where it is resonantly scattered by O+ ions. Due to this resonant scattering, the altitude profiles of the emission's intensity take on the characteristics of the F2 layer. These profiles are obtained while RAIDS is in limb scan mode, which surveys the atmosphere from approximately 75-325 km. The profiles are compared with coincident ionosonde and incoherent scatter radar measurements as well as forward models to test their response to changes in ionospheric conditions. Changes in the peak altitude and density of the daytime ionosphere become apparent in the emission profiles at varying latitudes, solar zenith angles, and local times. At higher latitudes the emission profiles peak at approximately 200 to 250 km, as expected during solar minimum. At lower latitudes the profile flattens out indicating a higher electron density. Changes in the peak intensity are also seen as a function of solar zenith angle. These data show that the emission profiles obtained by RAIDS of 83.4 nm airglow intensity provide, at a minimum, the means to qualitatively probe the global daytime ionosphere.