THE FOCUS OF THIS PROPOSAL IS RELATED TO MEASUREMENTS OF RAINFALL WITH THE NEWLY PURCHASED METEOROLOGICAL PARTICLE SPECTROMETER (MPS) BY NASA FOR DEPLOYMENT AT THE WALLOPS PRECIPITATION SCIENCE RESEARCH FACILITY. THIS INSTRUMENT WILL BE COLLOCATED WITH EXISTING INSTRUMENTS SUCH AS 2D?VIDEO DISDROMETER (2DVD) RAIN GAGES AND SUPPORTING INSTRUMENTATION UNDER THE UMBRELLA OF NASA S S?BAND NPOL RADAR. THERE ARE THREE MAIN OBJECTIVES: (I) MPS DATA QUALITY ASSESSMENT LEADING TO ESTABLISHING THE ACCURACY OF DROP SIZE DISTRIBUTIONS AND DROP FALL SPEEDS IN A VARIETY OF RAIN TYPES AND INTENSITIES; (II) CONSTRUCTION OF THE FULL DROP SIZE DISTRIBUTION (DSD) FROM DRIZZLE TO PRECIPITATION SIZES BY COMBINING DATA FROM THE MPS AND 2DVD TO DETERMINE THE UNDERLYING SHAPE; AND (III) DEVELOPING METHODS FOR DSD RETRIEVALS FROM NPOL RADAR MEASUREMENTS WITH APPLICATION TO THE GPM DUAL?FREQUENCY PRECIPITATION RADAR (DPR).