Results from the June 1998 Combined Ionospheric Campaign (CIC) will be presented. The CIC represents an attempt to focus a large number of different instruments on one interesting geophysical region. One of the objectives of these campaigns is to develop suitable data sets for ingestion into data assimilative models and also to serve as validation sets for these models. The Center for Ionospheric Research (CIR) at Applied Research Laboratories, University of Texas at Austin, has had several computerized ionospheric tomography (CIT) receivers deployed in the Caribbean region since July 1997. Analysis of the CIT data from the first CIC will be presented, and comparison with other data sets will be made. Analysis will initially focus on examining the total electron content (TEC) data from the CIT receivers and ground-based GPS TEC data and correlating it with other data sets. Subsequently, the analysis will shift to performing four-dimensional electron density estimations using the Ionospheric Data Assimilation 3D (IDA3D) algorithm developed at CIR. The resulting electron density estimates will be compared with other data sources both for accuracy of the technique and scientific investigations. ¿ 2001 American Geophysical Union