AN IMPORTANT GOAL OF THE DPR IS TO DERIVE RAIN RATE AND RAINDROP SIZE DISTRIBUTION (DSD). TO OBTAIN THE DSD SEVERAL DUAL-WAVELENGTH RADAR RETRIEVAL TECHNIQUES HAVE BEEN DEVELOPED. SOME OF THEM ARE BASED ON THE TECHNIQUE THAT USES THE DIFFERENTIAL FREQUENCY RATIO (DFR) I.E. THE DIFFERENCE IN DB OF RADAR REFLECTIVITIES BETWEEN TWO WAVELENGTHS TO LINK RADAR MEASUREMENTS TO THE DSD PARAMETERS WHILE OTHERS RELY ON OPTIMIZATION METHODS IN WHICH ONE OR MORE ADJUSTMENT FACTORS ARE USED TO MODIFY SOME NOMINAL RELATIONSHIPS BETWEEN THE PARAMETERS OF THE RADAR AND THE PRECIPITATION. BECAUSE OF NEARLY IDENTICAL REFLECTIVITIES FOR LIGHT RAIN AT KU- AND KA-BAND AND ALSO BECAUSE OF THE DOUBLE-VALUED SOLUTIONS TO DUAL-WAVELENGTH RADAR EQUATIONS FOR LIGHT-TO-MODERATE RAIN THE DSD AND RAIN RATE ESTIMATES OBTAINED BY DIRECTLY SOLVING THE RADAR EQUATIONS AS IN THE DFR-BASED APPROACHES ARE SUSCEPTIBLE TO LARGE UNCERTAINTIES. PERFORMANCE OF OPTIMIZATION METHODS ON THE OTHER HAND DEPENDS ON THEIR MODEL ASSUMPTIONS AND CONSTRAINTS USED FOR THE SOLUTIONS. WITH THE OVERARCHING GOAL OF IMPROVING THE DPR RETRIEVALS OF HYDROMETEOR PROFILES WE WILL STRIVE TO DEVELOP INNOVATIVE AND VERSATILE RETRIEVAL TECHNIQUES THAT WILL BENEFIT THE DPR NOT ONLY BY IMPROVING THE RETRIEVAL BUT ALSO BY SERVING AS AN ALTERNATIVE RESEARCH ALGORITHM THAT CAN BE USED TO EXAMINE THE CONSISTENCY OF THE DPR ESTIMATES ACROSS VARIOUS SURFACE BACKGROUNDS AND METEOROLOGICAL CONDITIONS. TO CIRCUMVENT THE DOUBLE-VALUE PROBLEM A MODIFIED DFR DENOTED BY DFR* WILL BE FORMULATED IN OUR PROPOSED STUDY. PRELIMINARY RESULTS REVEAL THAT AN OPTIMAL APPROACH THAT MAKES USE OF DFR* SHOWS GREAT POTENTIAL TO IMPROVE RETRIEVAL ACCURACY. IN THE PROPOSED STUDY WE WILL FOCUS ON EXAMINING THE POTENTIAL OF DFR* AND DEVELOPING THE DPR*-BASED ALGORITHMS. THE ALGORITHMS WILL BE INTEGRATED INTO AN OFFLINE OPERATIONAL SYSTEM WHERE THE INPUTS WILL BE IDENTICAL TO THOSE OF THE OPERATIONAL ALGORITHM SO THAT THE PRODUCTS FROM OPERATIONAL AND RESEARCH ALGORITHMS CAN BE COMPARED DIRECTLY. ANOTHER IMPORTANT TASK OF OUR STUDY IS TO ESTABLISH A FRAMEWORK/TEST-BED THAT ENABLES AN ACCURATE AND REALISTIC ASSESSMENT OF THE PERFORMANCE OF SINGLE- AND DUAL-WAVELENGTH PROFILING RETRIEVAL ALGORITHMS WITH THE GOAL OF IDENTIFYING THE SOURCES OF THE ERROR AND CHARACTERIZING THEIR UNCERTAINTIES. TO ACHIEVE THIS MEASURED TIME-SERIES DSD DATA WILL BE USED TO CONSTRUCT VERTICAL RAIN PROFILES. A FAIRLY ACCURATE RADAR BRIGHT-BAND MODEL COUPLED WITH MEASURED DSD WILL BE USED TO REPRESENT THE MELTING-LAYER RADAR SIGNATURES TO ACCOUNT FOR THE ATTENUATION AND UNCERTAINTIES ASSOCIATED WITH THE MELTING REGION. THE BASIC APPROACH CAN BE USED TO EVALUATE THE IMPACT OF DIFFERENT MODEL ASSUMPTIONS AND VARIOUS CONSTRAINTS ADOPTED IN THE RETRIEVAL ALGORITHMS. OUR FOCUS WILL BE ON EXAMINING AND IMPROVING RAIN AND DSD RETRIEVALS PARTICULARLY FOR THE DPR-OPERATIONAL AND DFR*-BASED ALGORITHMS. VALIDATIONS OF THE DPROPERATIONAL AND PROPOSED RESEARCH ALGORITHMS WILL BE MADE THROUGH INSTANTANEOUS COMPARISONS WITH THE SAME QUANTITIES OBTAINED FROM THE WELL-CALIBRATED GROUND-BASED RADAR MEASUREMENTS AND ESTIMATES. OUR PROPOSED RESEARCH PROJECT INCLUDES: 1) DEVELOPMENT OF A NEW TECHNIQUE FOR POTENTIALLY IMPROVING RETRIEVAL ACCURACY; 2) OFF-LINE IMPLEMENTATION OF AN ALTERNATIVE RESEARCH ALGORITHM TO EXAMINE THE CONSISTENCY OF THE DPR ESTIMATES; 3) ASSESSMENT OF THE DPROPERATIONAL ALGORITHM PERFORMANCES FOR IDENTIFYING THE SOURCES OF ERROR AND CHARACTERIZING THEIR UNCERTAINTIES; 4) ESTABLISHMENT OF PHYSICAL EVALUATION TEST-BED FOR ACCURATE AND REALISTIC ASSESSMENT OF THE PERFORMANCE OF THE PROFILING RETRIEVAL ALGORITHMS; 5) VALIDATION OF THE DPR MEASUREMENTS AND ITS ESTIMATES OBTAINED FROM THE OPERATIONAL AND DFR*-BASED ALGORITHMS. IT IS ANTICIPATED THAT OUR PROPOSED STUDY WILL PROVIDE INSIGHT INTO WAYS IN WHICH THE SINGLE- AND DUAL-WAVELENGTH RADAR ESTIMATES OF RAIN AND DSD CAN BE IMPROVED.