A technique for using measured ionosphere density gradients and GPS occultations for inferring the nighttime ionospheric electron density

Abstract

We present a technique for using the measured variations of ultraviolet emissions produced by radiative recombination at 911 or 1356 Å in conjunction with occultations of Global Positioning Systems (GPS) satellites observed from a low Earth-orbiting satellite to inter the two-dimensional structure of the nighttime ionosphere. We present the results of simulations that demonstrate the applicability and accuracy of the algorithm and observational concept. Our technique uses UV nadir radiances to infer the electron density gradients and total electron content measurements at the limb from an onboard GPS receiver to infer the altitude versus latitude structure of the ionosphere. To test our technique, we simulated "data" in a region of high gradient using the international reference ionosphere (IR-90; Bilitza [1990]) to generate the ionosphere. In the simulation the satellite was assumed to be in a polar orbit at 750 km, the proposed altitude for the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites. We simulated the limb total electron content (TEC) and the nadir radiances and superimposed noise on these "data." These data were then inverted using a newly developed algorithm that assumes a constant altitude variation of the electron density with latitude but scales this profile shape by the peak electron density, which varies with latitude. We find that our technique more accurately determines the electron density that direct inversion of the TEC data using Abel inversion techniques.