WITH RISING DEMANDS OF FOOD AND FIBER FROM A GROWING GLOBAL POPULATION AGRICULTURAL LANDSCAPE PLAYS AN INCREASINGLY IMPORTANT ROLE IN THE GLOBAL CARBON CYCLE. CROPLAND ALSO REPRESENTS ONE OF THE BIGGEST OPPORTUNITIES FOR CARBON SEQUESTRATION. ACCURATE QUANTIFICATION OF REGIONAL SCALE CROPLAND CARBON CYCLING IS CRITICAL FOR DESIGNING EFFECTIVE POLICIES AND MANAGEMENT PRACTICES THAT CAN CONTRIBUTE TO STABILIZING ATMOSPHERIC CO2 CONCENTRATIONS. A COMPREHENSIVE CARBON MONITORING SYSTEM SHOULD INCLUDE THE INTEGRATION OF BOTTOM-UP AND TOP-DOWN ESTIMATES OF CARBON FLUX. HOWEVER THE CURRENT CROPLAND-BASED CARBON MONITORING SYSTEMS FACE THE FOLLOWING CHALLENGES: (1) THEY PRIMARILY FOCUS ON BOTTOM-UP APPROACHES WITH LACK OF INTEGRATION AND CROSS-VERIFICATION BETWEEN BOTTOM-UP AND TO-DOWN APPROACHES; (2) THEY ARE LACK OF SPATIALLY EXPLICIT CHARACTERIZATION IN EITHER BOTTOM-UP PROCESS-BASED MODELS OR TOP-DOWN ATMOSPHERIC INVERSIONS. NOVEL SATELLITE DATA (INCLUDING SOLAR INDUCED CHLOROPHYLL FLUORESCENCE AND ATMOSPHERIC COLUMN-AVERAGE CO2 AND OTHER EXISTING NASA SATELLITE DATA PROVIDE UNIQUE OPPORTUNITIES IN ADDRESSING THESE CHALLENGES AND IMPROVING BOTH BOTTOM-UP AND TOP-DOWN APPROACHES. HERE WE PROPOSE ONE OF THE FIRST CARBON MONITORING SYSTEMS (CMS) THAT WILL INTEGRATE BOTH BOTTOM-UP AND TOP-DOWN APPROACHES TO JOINTLY QUANTIFY THE CARBON BUDGET FOR THE US CORN BELT. THE PROPOSAL PLANS TO ACHIEVE THREE MAJOR IMPROVEMENTS FOR BOTTOM-UP AND TOP-DOWN (TASK 1-3) WITH TASK 4 TO INTEGRATE AND SYNTHESIZE RESULTS FROM THE TWO APPROACHES TO GENERATE A CONSISTENT US CORN BELT CARBON FLUX PRODUCT INCLUDING A THOROUGH UNCERTAINTY ASSESSMENT COVERING THE PERIOD OF 2007 TO 2017. SPECIFICALLY THE FOUR TASKS ARE: TASK 1 (BOTTOM-UP APPROACH INVENTORY/SATELLITE): COMBINE USDA CROP STATISTICS-BASED AND SATELLITE-BASED SOLAR-INDUCED FLUORESCENCE (GOME-2 AND OCO-2) TO GENERATE AN IMPROVED 10 KM CARBON BUDGET INVENTORY (NPP GPP AND RA) FOR THE US CORN BELT. TASK 2 (BOTTOM-UP APPROACH MODELING/SATELLITE): ASSIMILATE MULTI-SOURCES OF SATELLITE DATA (MODIS LAI SMAP SOIL MOISTURE) AND NEWLY DERIVED CROP INVENTORY DATA (FROM TASK 1) INTO THE CLM-APSIM FRAMEWORK TO EXPLICITLY CONSTRAIN THE CROP PARAMETERS IN SPACE AND IMPROVE CARBON BUDGET SIMULATION. TASK 3 (TOP-DOWN APPROACH SATELLITE/IN-SITU): USE SATELLITE AND IN SITU DATA TOGETHER TO SOLVE FOR CO2 FLUXES AT HIGH-RESOLUTION IN A REGIONAL INVERSION OVER THE US CORN BELT. TASK 4 (BOTTOM-UP/TOP-DOWN INTEGRATION): INTEGRATE BOTTOM-UP AND TOP-DOWN APPROACHES TO JOINTLY CONSTRAIN THE CARBON BUDGET CROSS-VERIFY ESTIMATES AND PROVIDE ROBUST UNCERTAINTY CHARACTERIZATION. THIS CURRENT PROPOSAL TARGETS AT THE 2ND RESEARCH TOPIC THAT IS LISTED IN THE NASA CMS SOLICITATION I.E STUDIES THAT ADDRESS RESEARCH NEEDS TO ADVANCE REMOTE SENSING-BASED APPROACHES TO MONITORING REPORTING AND VERIFICATIONS. THE PROPOSED PROJECT DIRECTLY ADDRESSES NASA S STRATEGIC GOAL FOR THE EARTH SCIENCE TO STUDY PLANET EARTH FROM SPACE TO ADVANCE SCIENTIFIC UNDERSTANDING AND MEET SOCIETAL NEEDS . THE PROJECT WILL FULLY UTILIZE THE SIF AND XCO2 RETRIEVALS FROM THE NEW NASA SATELLITE OCO-2 AS WELL AS DATA FROM OTHER EXISTING NASA SATELLITE PRODUCTS (E.G. FROM SMAP MODIS CERES AND LANDSAT-BASED CROP DATA LAYER) TO DEVELOP IMPROVED CARBON FLUX ESTIMATIONS FROM BOTTOM-UP APPROACHES (INVENTORY-SATELLITE BASED AND PROCESS-MODEL BASED) AND TOP-DOWN APPROACHES (JOINTLY USING SATELLITE AND IN SITU DATA IN THE ATMOSPHERIC INVERSION). PUBLIC AND PRIVATE SECTORS CAN USE THIS PRODUCT TO INFORM AGRICULTURAL PRODUCTIVITY AND MANAGEMENTS WHICH WOULD FURTHER REALIZE THE VALUE OF NASA DATA. THIS EFFORT THUS CARRIES A GREAT PROMISE TO FURTHER CONSTRAIN THE REGIONAL AND GLOBAL CARBON CYCLE AND ALSO TO DIRECTLY ADDRESS ONE OF NASA S KEY SCIENTIFIC QUESTIONS FOR EARTH SCIENCE: HOW WILL CARBON CYCLE DYNAMICS AND ECOSYSTEM CHANGE IN THE FUTURE?