THE GPM CONSTELLATION CONCEPT USES OBSERVATIONS FROM A COLLECTION OF RESEARCH AND OPERATIONAL SPACEBORNE MICROWAVE RADIOMETERS TO PROVIDE HIGH-QUALITY FREQUENT GLOBAL PRECIPITATION ESTIMATES FOR HYDROLOGICAL AND OTHER APPLICATIONS. IT HAS SUBSEQUENTLY BEEN EXTENDED TO INCLUDE THE TRMM-ERA RADIOMETERS AND WILL SHORTLY BE EXTENDED BACK TO SSM/I ON BOARD DMSP F08 IN 1987. AS A RESULT AN INTERCALIBRATED BRIGHTNESS TEMPERATURE (I.E. LEVEL 1C TB) DATASET AND ASSOCIATED LEVEL 2 PRECIPITATION ESTIMATES WILL SOON BE AVAILABLE FOR A 30+ YEAR RECORD FROM A TOTAL OF 14 CONICAL-SCANNING MICROWAVE IMAGING AND 10 CROSS-TRACK SCANNING WATER VAPOR SOUNDING RADIOMETERS. THIS CONSTELLATION CONTINUES TO EVOLVE AS OLDER SENSORS IN THE GPM CONSTELLATION FAIL AND NEW ONES ARE LAUNCHED. THE FOCUS OF PRIOR INTERCALIBRATION AND RELATED ACTIVITIES THEREFORE MUST EVOLVE TO ADDRESS THESE CHANGES AS WELL AS TO EXTEND AND IMPROVE THE CONSISTENCY OF BOTH THE CURRENT GPM-ERA AND LONG-TERM PRECIPITATION DATA RECORDS. THE PROPOSED WORK WILL BUILD ON PROGRESS MADE UNDER PREVIOUS PMM FUNDED EFFORTS BY FOCUSING ON THE EVOLUTION OF THE RADIOMETER CONSTELLATION. SPECIFIC OBJECTIVES INCLUDE 1) ADDRESSING CHANGES TO THE RADIOMETER CONSTELLATION 2) IMPROVING QUALITY AND CONSISTENCY IN THE LEVEL 1C TB AND LEVEL 2A PRECIPITATION DATASETS AND 3) QUANTIFYING SENSOR-DEPENDENT PRECIPITATION UNCERTAINTIES. THE FIRST OBJECTIVE WILL FOCUS ON RESPONDING TO INSTRUMENT ISSUES IN AGING SENSORS CALIBRATION CHANGES TO PARTNER RADIOMETERS AND INCORPORATING NEWS SENSORS INTO THE CONSTELLATION. THIS WILL INVOLVE MONITORING THE EXISTING SENSORS INVESTIGATING CHARACTERIZING AND CORRECTING CALIBRATION DIFFERENCES FOR NEW SENSORS AND CHANGES TO PARTNER SENSORS AND WORKING WITH INSTRUMENT TEAMS FROM PARTNER AGENCIES (NOAA EUMETSAT JAXA ETC.). THE SECOND OBJECTIVE WILL INVOLVE REVISITING CORRECTIONS AND INTERCALIBRATION OFFSETS FOR CONSTELLATION RADIOMETERS WITH KNOWN ISSUES AS WELL AS WORKING TO EXPAND THE AVAILABLE LEVEL 1C DATA BY RE-EXAMINING REJECTED DATA FROM SENSORS SUCH AS AMSU AND SSMIS AND ACQUIRING ADDITIONAL DATA SUCH AS CORIOLIS WINDSAT. WE WILL ALSO WORK WITH ALGORITHM DEVELOPERS TO ENSURE THE CONSISTENT APPLICATION OF RADIATIVE TRANSFER MODELS PROPERLY ACCOUNTING FOR SENSOR DIFFERENCES AND REVISITING THE SENSOR CHANNEL ERRORS USED IN THE RETRIEVAL ALGORITHM. THE GOAL OF THESE OBJECTIVES IS TO MAXIMIZE THE AVAILABILITY QUALITY AND CONSISTENCY OF THE LEVEL 1C BRIGHTNESS TEMPERATURES AND LEVEL 2A PRECIPITATION ESTIMATES FROM THE CONSTELLATION MICROWAVE RADIOMETERS OVER THE FULL 30+ YEAR DATA RECORD. THE THIRD OBJECTIVE WILL FOCUS ON QUANTIFYING SENSOR-DEPENDENT UNCERTAINTIES IN THE RADIOMETER PRECIPITATION ESTIMATES AS A FUNCTION OF REGION AND TIME. WE WILL INVESTIGATE UNCERTAINTIES ASSOCIATED WITH BOTH SENSOR CALIBRATION AND DIFFERENCES IN PRECIPITATION-RELATED INFORMATION BETWEEN SENSORS DUE TO DATA QUALITY SPATIAL RESOLUTION CHANNEL FREQUENCIES ETC. A CRITICAL ASPECT OF THIS OBJECTIVE WILL BE TO ACCOUNT FOR BOTH RANDOM AND SYSTEMATIC UNCERTAINTIES AS WELL AS CORRELATED ERRORS FOR SPATIALLY AND TEMPORALLY AVERAGED PRECIPITATION ESTIMATES. WE WILL USE GPM DPR ESTIMATES AND GROUND VALIDATION DATASETS SUCH AS MRMS ALONG WITH SYNTHETIC RETRIEVALS TO INVESTIGATE HOW CHANGES IN SPATIAL RESOLUTION AND CHANNEL AVAILABILITY LEAD TO BIASES IN PRECIPITATION DETECTION AND INTENSITY OVER VARIOUS METEOROLOGICAL REGIMES AND/OR SURFACE TYPES. THE EXPECTED SIGNIFICANCE OF THIS WORK IS TO EXTEND AND IMPROVE THE AVAILABILITY AND CONSISTENCY OF HIGH-QUALITY PRECIPITATION ESTIMATES FROM THE RADIOMETER CONSTELLATION AND TO PROVIDE REALISTIC UNCERTAINTY ESTIMATES FOR CLIMATE AND OTHER APPLICATIONS.