The High Altitude MMIC Sounding Radiometer (HAMSR) was recently built by the Jet Propulsion Laboratory under the NASA Instrument Incubator Program. HAMSR is a combined atmospheric temperature and water vapor sounder operating in two millimeter wave bands – near 50 GHz and near 183 GHz. Using newly developed miniature technology, it is a compact, sensitive and accurate instrument. During the recent Convection and Moisture Experiment (CAMEX-4) – a multi-agency field campaign operating out of Jacksonville, FL from August 15 to September 25 2001 - HAMSR flew on the NASA ER-2 aircraft over a number of hurricanes and other convective systems in the Gulf of Mexico and the Atlantic. Preliminary data analysis has revealed substantial scattering, manifested as deep brightness temperature depression – sometimes as much as 100 K, observed in the 183-GHz channels while passing over intense convective cells. In some cases, the 50-GHz channels also exhibited scattering depression – usually in the centers of the most intense scattering regions observed in the 183-GHz channels. Such scattering signatures are presumed to be caused primarily by ice particles of various sizes above these convective cells.