To intercompare various techniques used in reconstructing tomographic images, and to benchmark those results with direct observations obtained by the incoherent scatter technique, an experimental campaign and subsequent analysis program-the Russian-American Tomography experiment (RATE)-were implemented in late 1993. Russian experiment teams from the Polar Geophysical Institute in Murmansk and Moscow State University joined with American investigators from the Phillips Laboratory and the Massachusetts Institute of Technology, and an array of four receiving stations was set up in the northeastern United States and in eastern Canada to obtain data for the tomographic reconstructions. Phase-difference and total-phase tomographic reconstruction techniques have been employed and are intercompared. The spatial/altitude distribution of ionospheric electron content was observed by the MIT Millstone Hill incoherent scatter radar that scanned the ionosphere in a plane parallel to the satellite overflights. We present preliminary reconstructions of the ionospheric structure observed during a severe midlatitude ionospheric storm that took place during the campaign. The drastic large-scale changes in the ionospheric structure that accompanied the November 1993 storm were well observed by the two diagnostic techniques.©1994 John Wiley & Sons Inc