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



[1] 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.