One of the most recent applications for tomographic imaging is the measurement of the electron density distribution in the ionosphere. This imaging system is a unique and challenging tomographic system because of the physical constraints of the system and the nature of the electron density distribution. To fully understand the potential and limitations of this imaging system, analysis of the resolving capabilities is needed. This article provides a review of current analysis methods for both system evaluation and characterization of the effects of individual degradation parameters. This article also presents a study of the effect of system configuration on the information content of projections.©1994 John Wiley & Sons Inc