RADIATIVE TRANSFER PROPERTIES OF CLOUDS PLAY AN IMPORTANT ROLE IN THE ENERGY BALANCE OF THE EARTH. NUMEROUS NASA PROGRAMS AND EXPERIMENTS ARE DIRECTED TO MEASURING THESE EFFECTS. IN-SITU MEASUREMENTS ARE CRITICAL FOR SUPPORTING SATELLITE-BORNE INSTRUMENTS. WHILE RESEARCH AIRCRAFT CARRY THE BEST IN-SITU INSTRUMENTS, THE AIRCRAFT AND INSTRUMENTS ARE TOO EXPENSIVE TO PROVIDE SUFFICIENT COVERAGE. ANASPHERE IS DEVELOPING A SUITE OF LOW-COST, BALLOON-BORNE INSTRUMENTS THAT CAN QUANTIFY ALL THREE CONDENSED PHASES OF WATER IN CLOUDS: SUPERCOOLED LIQUID, LIQUID, AND ICE. THE FIRST TWO INSTRUMENTS HAVE BEEN DEVELOPED AND ARE USED AROUND THE WORLD. THIS PROJECT IS DIRECTED TO DEVELOPING THE ICE WATER CONTENT (IWC) SENSOR TO COMPLETE THE TRIO. ADDITION OF AN IWC SENSOR WILL YIELD A SUITE OF INSTRUMENTS THAT CAN BE USED FOR MEASUREMENTS OF ALL CLOUD TYPES INCLUDING MIXED-PHASE CLOUDS. IN PHASE I, AN IWC SENSOR WHICH IS A DERIVATIVE OF THE PRECEDING SUCCESSFUL INSTRUMENTS WILL BE DEVELOPED. THIS WILL ENTAIL THE DEVELOPMENT OF A SUITABLE ICE COLLECTION MEDIUM AND ASSOCIATED CALIBRATION EQUATIONS. SUPPORTING WORK TO BE COMPLETED WILL INCLUDE OPTIMIZING ANASPHERE S ICING WIND TUNNEL FOR PURE ICE PARTICLE CONDITIONS. PHASE I WILL CONCLUDE WITH THE NEW IWC SENSOR BEING OPERATED IN THE ICING WIND TUNNEL.