The microwave emission properties of first-year sea ice were investigated from the R/V Polarstern during the Antarctic Winter Weddell Gyre Project in 1989. Radiometer measurements were made at 611 MHz and 10 GHz and were accompanied by video and visual observations. Using the theory of radiometric emission from a layered medium, a method for deriving sea ice thickness from radiometer data is developed and tested. The model is based on an incoherent reflection process and predicts that the emissivity of saline ice increases monotonically with increasing ice thickness until saturation occurs. 22,569 22,570 MENASHI ET AL.' LoW-FREQUENCY PASSIVE-MICROWAVE OBSERVATIONS OF SEA ICE 0i Greenland, Nature, 345, 795-797, 1990. Wadhams, P., M. A. Lange, and S. F. Ackey, The thickness distribution across the Atlantic sector of the Antarctic Ocean in midwinter, J. Geophys. Res., A. W. Lohanick, Naval Oceanographic and Atmospheric Research Laboratory, Polar Oceanography Branch Office, Hanover, NH 03755.