The October 1984 Shuttle Imaging Radar B (SIR-B) flight made three radar passes over the Weddell Sea ice, providing the first high-resolution look at the Weddell marginal ice zone properties. Using these data, this paper discusses the effect of ocean waves on the radar return at the ice edge and compares ice concentrations derived from the SIR-B with coincident concentrations from the Nimbus 7 scanning multichannel microwave radiometer (SMMR). The comparison of the SIR and SMMR concentrations is possible because /SIR cross-track width and the diameter of the SMMR 37-GHz integrated field-of-view are both about 30 km. The SIR ice concentrations are computed in two ways: first, using a training area classification scheme at the Jet Propulsion Laboratory (JPL); second, using a manual classification method at the Scott Polar Research Institute. The SMMR ice concentrations are calculated using the Goddard Space Flight Center algorithm. At the ice edge, where there were no coincident SMMR data and where ice bands predominated to yield an ice concentration of the order or 10% of less, comparison of the two different analysis techniques on the same images showed that, for the JPL technique to avoid classifying some of the open water as ice, two classes of open water must be defined. These two classes accounted for the rougher ocean surface upwind of the bands and the smoother downwind surface. In the ice interior, comparison of the coincident SIR and SMMR ice concentrations shows that for concentrations greater than 40%, which was the smallest concentration jointly observed, the mean difference between the two data sets for 12 points is 2% and the standard deviation is 7%. ¿ American Geophysical Union 1987