MEASUREMENTS OF CO2 CONCENTRATIONS OVER HALF A CENTURY HAVE REVEALED THAT THE TERRESTRIAL BIOSPHERE HAS ACCUMULATED CARBON FORDECADES AT ABOUT A QUARTER OF THE RATE OF FOSSIL FUEL EMISSIONS. THE TERRESTRIAL CARBON SINK MAY OR MAY NOT BE CLOSE TO SATURATING[CANADELL ET AL. 2007; LEQUERE ET AL. 2009; HAYES ET AL. 2011; PAN ET AL. 2011; BALLANTYNE ET AL. 2012] WITH POTENTIALLY DIRECONSEQUENCES FOR AMPLIFICATION OF FUTURE CLIMATE CHANGE [COX ET AL. 2000; FUNG ET AL. 2005; FRIEDLINGSTEIN ET AL. 2006; LUO 2007; REAYET AL. 2007; HUNTINGFORD ET AL. 2008; GREGORY ET AL. 2009]. ATMOSPHERIC CO2 DATA CLEARLY CONTAINS INFORMATION THAT CAN BE USED TOBETTER UNDERSTAND SOURCES AND SINKS OF CARBON. HOWEVER CONCENTRATION DATA CONTAIN A MIX OF SIGNALS FROM A VARIETY OF UPWIND SOURCESAND SINKS WHICH FORCES ONE TO EMPLOY ATMOSPHERIC FLUX INVERSION TECHNIQUES A BLEND OF ATMOSPHERIC TRANSPORT MODELING AND STATISTICALMODELING TO DETANGLE THE CONVOLUTION OF SURFACE CO2 FLUXES AND ATMOSPHERIC TRANSPORT AND ALLOW INSIGHT INTO REGIONAL CARBON FLUXPROCESSES.IN THE LAST OCO-2 SCIENCE TEAM CALL WE WERE SELECTED (#NNX15AG93G) TO DEVELOP A PULSE-BASED INVERSION SYSTEM WHERE CO2 FLUXCORRECTIONS TOOK THE FORM OF LOW ORDER SEASONAL HARMONICS OF CO2 FLUX PARTITIONED SPATIALLY AND BY PLANT FUNCTIONAL TYPE FROM THESIB4 BIOSPHERE MODEL. WE ALSO PROPOSED TO INCORPORATE OCO-2 SOLAR INDUCED FLUORESCENCE (SIF) MEASUREMENTS INTO THE INVERSIONSCHEME AS A CONSTRAINT TO GPP. WE'RE IN OUR THIRD YEAR OF THE PROPOSAL AND HAVE BUILT THE INVERSION SYSTEM AND USED IT IN SEVERALCAPACITIES (SECTION 2). WE ARE USING OUR LAST YEAR OF THE PROPOSAL TO FOCUS ON INCORPORATING SIF BUT HAVE NOTICED SEVERAL DEFICIENCIESWITH ITS USE AS A DIRECT CONSTRAINT ON GPP IN THE INVERSION.WE THEREFORE ARE PROPOSING AN EFFORT TO CONTINUE PERFORMING INVERSE MODELING OF OCO-2 DATA (AND OCO-3 WHEN AVAILABLE) WHERE WEWILL FOCUS ON FOUR ITEMS. FIRST WE WILL INCORPORATE THE USE OF GPP FLUX DATA FROM EDDY COVARIANCE TOWERS INTO THE INVERSION FRAMEWORKTO OVERCOME AN OBSTACLE IN THE USE OF OCO-2 SIF TO CONSTRAIN REGIONAL GPP AND RESPIRATION. SECOND AS SOMEWHAT OF A BONUS THISADDITIONAL EDDY FLUX CONSTRAINT WILL ALLOW THE CONSTRAINING OF A LEAF-TO-CANOPY SCALING FACTOR SPECIFIC TO FLUORESCENCE TO BE ESTIMATED EMPIRICALLY AS PART OF THE INVERSION FRAMEWORK. THIRD WE WILL INVESTIGATE THE MODIFICATIONS OF RADIATION CODE IN SIB4 TO BETTER MODELSIF FROM FIRST PRINCIPLES ALLOWING BOTTOM-UP TOP-DOWN COMPARISONS OF A LEAF-TO-CANOPY PFT SPECIFIC SCALING FACTOR. FINALLY WE WILLCONTINUE TO PERFORM ATMOSPHERIC INVERSIONS OF EMERGING OCO-2 XCO2 DATA SETS AS WE HAVE FOR TWO YEARS AND ASSIST IN BOTH INTERCOMPARISONEXERCISES (MIP) TRANSPORT ERROR -- CARBON FLUX RELATIONSHIPS (JOINTLY WITH ACT-A CAMPAIGN) AND XCO2 L2 BIAS EVALUATIONEXERCISES.