Remote sensing of nighttime F region peak height and peak density using ultraviolet line ratios

Abstract

We present a newly developed algorithm for simultaneously inferring the peak height and peak density of the O+ ions in the nighttime ionosphere. The technique relies on the simultaneous observation of the emissions of atomic oxygen at 130.4 and 135.6 nm that are primarily produced by radiative recombination, a natural decay process of the ionosphere. The 135.6 nm emission has become the workhorse for sensing O+ distribution from space from low‐Earth platforms where it has been used to infer the peak electron density. A previous study showed that the line ratio of the intensity of the 130.4/135.6 nm radiances is sensitive to the peak height of the ionosphere, as the ratio of the two radiances is dependent on the overlap of the O+ distribution with the thermospheric O layer. We present a new parametric study of these emissions using a new algorithm that permits the retrieval of the peak electron density and the peak height of the F region ionosphere from the measured radiances of the 135.6 and 130.4 nm emissions. We examine the sensitivity of the retrievals to the ionospheric and thermospheric state and to the signal‐to‐noise ratio of the observations. This new technique enables the determination of the peak height and peak density of the nighttime F region ionosphere as functions of latitude and longitude from nadir‐viewing geostationary satellites.