TOMOGRAPHIC RECONSTRUCTION OF THE IONOSPHERE OVER NORTH-AMERICA WITH COMPARISONS TO GROUND-BASED RADAR

Data collection for the first ground-based ionospheric tomography camp aign in North America was conducted over a 48-hour period in mid-Novem ber 1991. The data consist of records of ionospheric total electron co ntent (TEC) from a number of passes of the U. S. Navy Navigation Satel lite System spacecraft over a chain of ground-based receiving stations . Data collection and reduction techniques are discussed; these includ e the determination of absolute TEC from the different phase advances induced by the ionosphere in each component of the dual-frequency spac ecraft signal. The use of tomographic methods to reconstruct ionospher ic electron densities over a two-dimensional (2-D) region of the Earth 's ionosphere at a number of different times is demonstrated. Specific ally, two distinct tomographic methods, the algebraic reconstruction t echnique and a maximum entropy method, are used to mathematically inve rt the records of TEC. The resulting 2-D contour ''maps'' of ionospher ic electron density are then compared to similar maps produced by the Millstone Hill incoherent backscatter radar facility located at Westfo rd, Massachusetts. Both qualitative and quantitative measures of agree ment among the different reconstructions and the radar maps are presen ted. The behavior of the ionosphere over the course of the experiment is discussed.