CHARACTERIZING THE SINGLE SCATTERING PROPERTIES (SSPS) OF REALISTIC HYDROMETEORS IS IMMEDIATELY AND INCREASINGLY NEEDED FOR A BETTER INTERPRETATION AND ANALYSIS OF PASSIVE AND ACTIVE MICROWAVE PRECIPITATION OBSERVATIONS. A FAITHFUL REPRESENTATION OF THE EM BEHAVIOR OF PRECIPITATION PARTICLES REQUIRES A NUMERICALLY EFFICIENT MODEL TO RIGOROUSLY CALCULATE THE SCATTERING BY ELECTRICALLY LARGE PARTICLES WITH REALISTIC COMPLEX SHAPES AND DIELECTRIC PROPERTIES AND THIS OVER A SUFFICIENTLY LARGE NUMBER OF PARTICLE ORIENTATIONS. THE DISCRETE DIPOLE APPROXIMATION (DDA) IS ONE OF THE MAIN APPROACHES THAT HAS BEEN USED TO THIS END IN THE LAST DECADE BEING A GEOMETRY-FLEXIBLE AND NUMERICALLY LOW-COST TECHNIQUE FOR COMPUTING SCATTERING AND ABSORPTION OF LIGHT BY PARTICLES OF ARBITRARY GEOMETRY AND INTERNAL DIELECTRIC COMPOSITION. THE DDA IS A POWERFUL TECHNIQUE BASED ON MAPPING THE COMPLEX-SHAPED PARTICLE INTO AN ARRAY OF N DIPOLES THAT TOGETHER REPRODUCE THE SHAPE AND INTERNAL OPTICAL RESPONSE OF THE ORIGINAL PARTICLE. NEVERTHELESS THE DDA PRESENTS TWO MAJOR LIMITATIONS. FIRST THE ACCURACY OF THIS APPROXIMATION STRONGLY DEPENDS ON THE PRECISION OF THE PARTICLE DISCRETIZATION NAMELY THE INTER-DIPOLE DISTANCE D WHICH MUST FULFILL THE VALIDITY CRITERIA M KD<0.5 WHERE M IS THE COMPLEX REFRACTIVE INDEX AND K IS WAVELENGTH NUMBER. THEN SINCE THE CURRENT IMPLEMENTATIONS OF THE DDA (DDSCAT AND ADDA) ARE ITERATIVE-SOLVER BASED THE CALCULATION OF ORIENTATIONALLY-AVERAGED SSPS REQUIRES REPEATEDLY SOLVING COMPUTATIONALLY DEMANDING LINEAR EQUATIONS FOR EACH PARTICLE ORIENTATION. IN AGGREGATE TERMS BEING BASED ON ITERATIVE METHODS THE DDA IS TODAY EXCESSIVELY SLOW FOR LARGE PARTICLE SIZE PARAMETERS (X=KA) LARGE VALUES OF THE REFRACTIVE INDEX LARGE NUMBERS OF DIPOLES AND LARGE TARGET ORIENTATIONS. FOR EXAMPLE TH CALCULATION OF THE SCATTERING PROPERTIES OF ONE SINGLE MEDIUM SIZE SNOW AGGREGATE (X=24) COMPOSED OF N = 140 896 DIPOLES OVER ONLY 2000 TARGET ORIENTATIONS AT F = 200 GHZ REQUIRES ALMOST 1 YEAR OF CPU TIME WITH DDSCAT. TO OVERCOME THIS LIMITATION WE HAVE CHOSEN TO APPLY RATHER A DIRECT SOLVER-BASED METHOD KNOWN AS THE CHARACTERISTIC BASIS FUNCTION METHOD (CBFM). THIS DOMAIN DECOMPOSITION METHOD IS BASED ON THE GENERATION OF A NEW SET OF BASIS FUNCTION ADAPTED TO THE GEOMETRY OF THE SCATTERER IN ORDER TO SIGNIFICANTLY REDUCE THE NUMERICAL SIZE OF THE INITIAL EM PROBLEM. THIS ENABLES US TO USE A DIRECT SOLVER FOR THE RESOLUTION OF THE FINAL COMPRESSED SYSTEM OF LINEAR EQUATIONS WHICH IS BETTER ADAPTED THAN AN ITERATIVE SOLVER FOR MULTIPLE RIG HAND SIDES PROBLEMS. NAMELY THE CBFM WILL ENABLE US TO TRANSFORM THE ORIGINAL PROBLEM OF SIZE 3N 3N TO A COMPRESSED ONE OF SIZE K K WITH K<<3N THEN INVERT THE FINAL COMPRESSED MATRIX ONLY ONCE FOR ALL THE NEEDED INCIDENT DIRECTIONS (EQUIVALENT TO TARGET ORIENTATION WITH A FIXED INCIDENT DIRECTION). THUS THE CBFM-BASED MODEL IS MUCH BETTER ADAPTED FOR THE CALCULATION OF EM SCATTERING BY NUMERICALLY AND ELECTRICALLY LARGER PARTICLES WITH A LARGER NUMBER OF PARTICLE ORIENTATIONS. APPLIED TO NUMERICALLY MEDIUM SNOW PARTICLES OUR CBFM-BASED MODEL FOR NUMERICALLY EFFICIENT SCATTERING BY COMPLEX-SHAPED PARTICLES (NESCOP) HAS BEEN SHOWN IN GOOD AGREEMENT WITH DDSCAT WHILE PROVIDING A DRAMATIC GAIN IN CPU TIME REDUCING IT FOR EXAMPLE FOR THE SNOW AGGREGATE ABOVE FROM 1 YEAR TO FEW HOURS. THESE PROMISING RESULTS ARE SPURRING US TO CONTINUE OUR EFFORTS TO IMPROVE THE ACCURACY AND COMPUTATIONAL PERFORMANCE OF NESCOP IN ORDER TO OVERCOME THE DIFFICULTIES THAT THE PMM COMMUNITY IS FACING TODAY TO CALCULATE THE SSPS OF REALISTIC SOLID AND MIXED-PHASE HYDROMETEORS. IF THIS PROJECT ACHIEVES ITS GOALS NESCOP WILL ENABLE US NOT ONLY TO SUBSTANTIALLY REDUCE THE TIME COST ASSOCIATED TO LARGE COMPLEX-SHAPED HYDROMETEORS WITH LARGE NUMBER OF PARTICLE ORIENTATIONS BUT MORE IT WILL ALLOW US TO RUN CALCULATIONS THAT ARE IMPOSSIBLE TO PERFORM WITH AVAILABLE DDA IMPLEMENTATIONS.