Theoretical studies have shown the potential scientific value of multi-spacecraft radio tomographic imaging of the magnetosphere. The <10 RE WIND perigee passes during August 2000 afforded a unique opportunity to test and verify the capabilities of radio tomography by measuring interspacecraft electromagnetic wave propagation parameters using the Radio Plasma Imager (RPI) on IMAGE as the transmitter and the WAVES instrument on WIND as the receiver. The primary goal of this experiment was to measure Faraday rotation variations in the RPI signal and interpret them in terms of the path-integrated magnetic field and electron density. A special 6 W linearly-polarized 828 kHz RPI signal was clearly detected by WAVES more than 6 RE away and showed a distinct signature of time-varying Faraday rotation. We show how changes in the path-integrated electron density/magnetic field product can be unambiguously measured from this continuous, low signal to noise ratio, single frequency measurement. ¿ 2001 American Geophysical Union