A new strategy for ionospheric remote sensing using the 130.4/135.6 nm airglow intensity ratios

We demonstrate here that global-scale determination of a key ionospheric parameter, the peak height of the F₂ region (h_mF₂), can be obtained by making a simple ratio measurement of the atomic oxygen 130.4 and 135.6 nm emissions in the far-ultraviolet nightglow with a nadir-viewing system such as a pair of photometers suitable for flight on a CubeSat. We further demonstrate that measurements from an altitude that is within the typical range of nighttime h_mF₂ \simeq 250−450 km can provide the ratios that are needed for retrieval of the h_mF₂. Our study is conducted mostly through numerical simulations by using radiative transfer models of the two emissions coupled with empirical models of the atmosphere and ionosphere. Modeling results show that the relationship between the h_mF₂ and the intensity ratio is sensitive to the altitude from which the emissions are observed, primarily because of the distinctly different degrees of resonant scattering of the two emissions in the atmosphere. A roughly quadratic relationship can be established for observations from an orbit of ~400 km, which enables h_mF₂ retrieval. Parametric analysis indicates that the relationship can be affected by the ambient atmospheric conditions through resonant scattering and O₂ absorption. For typical nighttime conditions with h_mF₂ \simeq 250−450 km, retrieval of the h_mF₂ from synthetic observations shows that the typical errors are only a few kilometers (up to ~20 km), depending on the accuracy of the ambient conditions predicted by the empirical models. Our findings pave the way for use of the 130.4/135.6 nm intensity ratios for global-scale monitoring of the nighttime ionosphere at mid to low latitudes.