A New Algorithm for Sensing the Global Daytime Ionosphere from Space 
 
K. F. Dymond and J. M. Picone 
Space Science Division 
Naval Research Laboratory 
Washington, DC 20375 
 
Abstract 
 
We present and demonstrate a newly developed algorithm for inferring key 
information about the distribution of O+ ions in the dayside ionosphere using 
measurements of the nadir radiance of the 83.4 nm emission.  The 83.4 nm 
emission is produced during the daytime primarily by photoionization excitation 
of O atoms to produce O+ ions.   The 83.4 nm photons enter the F-region 
ionosphere where they are resonantly scattered by the O+ ions several times 
before they escape to space.  The multiple resonant scattering of the photons 
impresses information about the density and distribution of the O+ ions on the 
radiation field.  Previous studies of the 83.4 nm emission have focused on 
retrieving information about the density and distribution of the O+ on the 
Earth’s limb as viewed from low-Earth orbiting limb scanning systems.  We 
present a newly developed algorithm that inverts the emission when viewed in the 
nadir, either from low-Earth orbit or from geostationary orbit.  This algorithm 
enables, for the first time, imaging of the Earth’s dayside ionosphere from 
a high altitude platform analogous to imaging of tropospheric weather from 
geostationary satellites.