Ionospheric nighttime electron density profiles were derived using 1356-¿ ultraviolet limb scans from the Low-Resolution Airglow and Aurora Spectrograph (LORAAS) instrument on the Advanced Research and Global Observing Satellite (ARGOS). Successive limb scans along the Sun-synchronous orbit were inverted using a tomographic algorithm and were used to reconstruct the ionosphere in latitude and altitude in the 0230 local time frame. Total electron content (TEC) as a function of latitude was obtained by vertically integrating the tomographic densities. Similarly, dual-frequency radar altimeter on TOPEX/Poseidon provided estimates of vertically integrated TEC along the satellite orbit. Comparisons were made between coincident ARGOS and TOPEX satellite passes for several days in December 1999 and November 2000. The comparisons demonstrate the performance of the tomographic algorithm to reconstruct latitudinal variations in the ionosphere, namely the location and magnitude of the nighttime tropical arcs. The comparisons also demonstrate a technique for independently calibrating the limb imager sensitivity.