URBAN ECOSYSTEMS OFFSET GREENHOUSE GAS EMISSIONS REMOVE AIR AND WATER POLLUTANTS COOL LOCAL CLIMATE AND IMPROVE PUBLIC HEALTH BUT THEIR INFLUENCE ON CARBON SEQUESTRATION HAS RECEIVED LESS ATTENTION AND REMAINS POORLY CONSTRAINED. HERE WE PROPOSE TO QUANTIFY URBAN BIOGENIC CO2 FLUXES IN THE LOS ANGELES (LA) BASIN FOR A TOTAL OF 3 YEARS TO DISENTANGLE ANTHROPOGENIC VS BIOGENIC CONTRIBUTIONS TO URBAN CARBON CYCLING AND ATMOSPHERIC CO2 ENHANCEMENTS. A PRIMARY OUTCOME WILL BE A GENERALIZED MODEL-OBSERVATION FRAMEWORK TO STUDY GLOBAL URBAN CO2 SOURCE AND SINK PROCESSES DRIVEN BY REMOTE SENSING OBSERVATIONS OF SOLAR INDUCED CHLOROPHYLL FLUORESCENCE (SIF) FROM NASA OCO-2 OCO-3 AND GEOCARB MISSIONS. OUR STRATEGY LEVERAGES THE DENSE SIF REMOTE SENSING OBSERVING NETWORK IN LA TO CONSTRAIN DIURNAL SPATIAL AND SEASONAL VARIABILITY IN PHOTOSYNTHETIC ACTIVITY ACROSS DIVERSE URBAN AND NATURAL LANDSCAPES IN LA AND FEEDS THIS INFORMATION INTO A NEW URBAN LIGHT USE EFFICIENCY MODEL THE URBAN VEGETATION PHOTOSYNTHESIS AND RESPIRATION MODEL (URBANVPRM) TO ESTIMATE GROSS AND NET BIOSPHERE CO2 FLUX. SIF OBSERVATIONS FROM OCO-2 AND EXPECTED FROM OCO-3 WILL PROVIDE SMALL FOOTPRINT (3 KM2) AND HIGH DATA ACQUISITION NEEDED TO RESOLVE LANDSCAPE SCALE PROCESSES WITH OCO-3 PROVIDING THE ADDED BENEFIT OF HIGH RESOLUTION SPATIAL MAPPING AND DIURNAL ACQUISITION OVER CITIES SIMILAR TO EXPECTED GEOCARB MAPPING ABILITIES. TO OPTIMIZE INFORMATION CONTENT OF OCO-2 AND OCO-3 WE WILL USE DIURNALLY INTEGRATED AND SPATIALLY EXPLICIT HYPERSPECTRAL MEASUREMENTS FROM THE CALIFORNIA LABORATORY FOR ATMOSPHERIC REMOTE SENSING FOURIER TRANSFORM SPECTROMETER (CLARS-FTS) ON MT WILSON (SITTING ABOVE LA) TO CALIBRATE AND SCALE OCO-2/OCO-3 SIF OVERPASSES ACROSS THE LA BASIN TO BETTER CHARACTERIZE SATELLITE DERIVED DAILY INTEGRATED SIF VARIABILITY ACROSS DIVERSE NATURAL AND URBAN ECOSYSTEMS. WE WILL MAP CLARS OCO-2 AND OCO-3 SIF ONTO A SPATIALLY CONTINUOUS GRID USING DATA FUSION WITH LANDSAT 8 EVI AND INTEGRATE INTO URBANVPRM TO PREDICT DIURNAL SEASONAL AND INTERANNUAL PHOTOSYNTHETIC RESPIRATION NET CO2 FLUXES IN LA. FINALLY WE WILL USE WRF-STILT FOOTPRINT ANALYSIS TO PREDICT CO2 SIGNALS IN COMPARISON TO ONGOING HOURLY CO2 OBSERVATIONS FROM THE LA IN SITU GHG TOWER NETWORK ACCOUNTING FOR BIOGENIC (URBANVPRM) AND FOSSIL (FROM HESTIA) URBAN SOURCES. OUR PROPOSAL IS CAPTURED IN 3 OBJECTIVES: OBJECTIVE 1: DELIVER CALIBRATED GAP-FILLED AND SPATIOTEMPORALLY INTEGRATED PHOTOSYNTHESIS INDEX OVER LA. OBJECTIVE 2: QUANTIFY URBAN BIOGENIC CO2 FLUXES OVER THE LA MEGACITY AND RANK URBAN VEGETATION TYPES IN TERMS OF ABILITY TO STORE CARBON AND MITIGATE ANTHROPOGENIC EMISSIONS IN COMPARISON TO FOSSIL FUEL INVENTORIES. OBJECTIVE 3: VALIDATE AND ATTRIBUTE DOMINATE FOSSIL FUEL AND BIOGENIC CO2 FLUXES AGAINST TOWER IN SITU CO2 AND 14CO2 DATA. THIS PROJECT WILL PROVIDE A TIMELY FRAMEWORK TO INGEST THE LARGER SET OF ECOSYSTEM DYNAMICS OBSERVATIONS (GEDI HISUI AND ECOSTRESS) EXPECTED FROM THE INTERNATIONAL SPACE STATION STARTING IN 2018 AND AN IMPORTANT TEST CASE TO INGEST HIGH SPATIAL RESOLUTION SIF DATA FROM GEOCARB IN LEVEL 3 AND 4 MODEL ENHANCED C PRODUCTS. BY COMBINING OCO-2/OCO-3 SIF WITH SENSORS FROM CLARS AND LANDSAT 8 TO QUANTIFY TERRESTRIAL AND ANTHROPOGENIC EMISSIONS OUR PROPOSAL MEETS THE FOLLOWING TASKS: "NEW RESEARCH AND INNOVATIVE ANALYSIS USING DATA FROM OCO-2 COMBINED WITH OTHER SENSORS (E.G. GOSAT OTHER A-TRAIN SENSORS SMAP) TO ADVANCE THE SCIENCE GOALS OF OCO-2 IN ORDER TO SIGNIFICANTLY ADVANCE OUR UNDERSTANDING OF CARBON CYCLE PROCESSES (BOTH OCEAN AND TERRESTRIAL) AND/OR ANTHROPOGENIC EMISSIONS " AND "STUDIES THAT TAKE FULL ADVANTAGE OF THE SOLAR INDUCED FLUORESCENCE DATA PRODUCT FROM OCO-2/OCO-3 IN COMBINATION WITH THE LEVEL 2 CO2 PRODUCT AND OTHER SATELLITE BASED OBSERVATIONS TO SIGNIFICANTLY ADVANCE OUT UNDERSTANDING OF CARBON CYCLE PROCESSES."