SUBOPTIMAL WEIGHTING OF THE INFORMATION PROVIDED BY MODELS AND MEASUREMENTS POSES A FUNDAMENTAL LIMITATION ON THE PERFORMANCE OF ATMOSPHERIC DATA ASSIMILATION SYSTEMS (DAS).THIS PROJECT AIMS TO OPTIMIZE THE INFORMATION CONTENT OF OBSERVATIONS IN THE NASA GODDARD EARTH OBSERVING SYSTEM (GEOS) DAS BY COMPLETING THE FOLLOWING RESEARCH OBJECTIVES: A POSTERIORI STATISTICAL ANALYSIS OF DATA ASSIMILATION PRODUCTS AND DIAGNOSIS OF THE OBSERVATIONAL ERROR CORRELATION STRUCTURES; IDENTIFICATION OF THOSE STATE AND OBSERVING SYSTEM COMPONENTS WHOSE IMPROVED ESTIMATES OF THE ERROR STATISTICS WILL CONTRIBUTE MOST TO REDUCING THE ANALYSIS AND FORECAST UNCERTAINTIES; A PRIORI QUANTIFICATION OF THE GAIN IN FORECAST SKILL THAT MAY ACHIEVED FROM ADJUSTMENTS IN THE ERROR COVARIANCE MODELS; ERROR COVARIANCE PARAMETER TUNING AND VALIDATION USING OBSERVING SYSTEM EXPERIMENTS (OSES).THIS RESEARCH WILL ESTABLISH A SYNERGISTIC LINK BETWEEN VARIOUS METHODOLOGIES TO ANALYZE THE DAS PERFORMANCE: ADJOINT-DAS OBSERVATION SENSITIVITY AND IMPACT ASSESSMENT ERROR COVARIANCE SENSITIVITY AND A POSTERIORI CONSISTENCY DIAGNOSIS. EMPHASIS WILL BE PLACED ON THE DIAGNOSIS AND FORECAST IMPACT ESTIMATION OF THE OBSERVATION ERROR COVARIANCES FOR THE REMOTE SENSING INSTRUMENTS AND ON THE OPTIMAL WEIGHTING IN THE DAS BETWEEN THE INFORMATION PROVIDED BY THE PRIOR STATE ESTIMATE (BACKGROUND) AND THE INFORMATION PROVIDED BY THE OBSERVING SYSTEM. ADVANCED MATHEMATICAL TOOLS WILL BE USED TO DEVELOP NOVEL ERROR COVARIANCE MODELS THAT INCORPORATE BOTH SPATIAL AND INSTRUMENT INTERCHANNEL ERROR CORRELATIONS.THE RESEARCH OBJECTIVES ARE DIRECTLY RELATED TO THE PROGRAMMATIC PRIORITY OF THE NASA MAP PROGRAM TO CHARACTERIZE AND REDUCE UNCERTAINTIES IN THE MODELS AND DATA ASSIMILATION PRODUCTS. THIS PROJECT WILL DEVELOP THE TOOLS THAT ARE NECESSARY TO OPTIMIZE THE GEOS DAS CAPABILITIES TO ASSIMILATE HIGH-RESOLUTION TIME-DISTRIBUTED DATA AND TO MAXIMIZE THE SATELLITE DATA UTILITY. THE PROJECT WILL LEVERAGE CURRENT RESEARCH AT NASA GLOBAL MODELING AND ASSIMILATION OFFICE (GMAO) ON OBSERVATION IMPACT ASSESSMENT AND OBSERVING SYSTEM SIMULATION EXPERIMENTS (OSSES) AND WILL CONTRIBUTE TO THE NASA/GMAO EFFORTS TO ACHIEVE AN OPTIMAL USE OF SATELLITE AND IN SITU OBSERVATIONS IN THE GEOS DAS.