A New Algorithm for Sensing the Global Nightside Ionosphere from Space 
 
 
K. F. Dymond 
Space Science Division 
Naval Research Laboratory 
Washington, DC 20375 
  
Abstract 
 
We present the results of simulations of a newly developed algorithm for 
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.  These emissions 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.  When viewing in the nadir, the 135.6 nm 
emission has been used to infer the peak electron density and if a vertical 
distribution of O+ ions is assumed, the total electron content.  By adding the 
130.4 nm emission to the mix, it has been shown that in addition to the 
determination of the peak electron density from the 135.6 nm emission, it is 
possible to infer the peak height of the O+ ions from the ratio of the two 
radiances as this quantity is dependent on the overlap of the O+ distributi 
 on with the background O density.  We present a new study of these emissions 
and 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 also examine the sensitivity of the retrievals 
to the background atmospheric state and to the signal-to-noise ratio of the 
observations.  This algorithm enables the determination of the peak height and 
peak density of the nighttime F-region ionosphere from geostationary platforms.