WE PROPOSE A STUDY FOCUSED ON USING SATELLITE REMOTE SENSING TO ADDRESS THE BASIC QUESTION: WHAT CONTROLS THE RESPONSE OF PHOTOSYNTHESIS IN AMAZONIAN FORESTS TO SEASONAL AND INTER-ANNUAL VARIATIONS IN CLIMATE? THIS QUESTION DESPITE ITS APPARENT SIMPLICITY REMAINS DIFFICULT FOR MODERN EARTH SYSTEM MODELS TO ANSWER AND IS ALSO THE SUBJECT OF CONTINUING CONTROVERSY IN THE REMOTE-SENSING LITERATURE. IN THE MODELING ARENA CUTTING-EDGE EARTH SYSTEM MODELS (ESM'S) SHOW SIGNIFICANT DIVERGENCE IN THEIR SEASONAL PATTERNS OF PHOTOSYNTHESIS FROM OBSERVED WHOLE-SYSTEM PHOTOSYNTHETIC FLUXES AT SITES IN THE CENTRAL AMAZON. AT THE SAME TIME SATELLITE BASED REMOTE SENSING STUDIES CONTINUE A LONG-STANDING DEBATE ABOUT WHETHER FOREST PHOTOSYNTHETIC SEASONALITY DERIVED FROM MODISVEGETATION INDICES IS AN ARTIFACT OF SUN-SENSOR GEOMETRY OR OF ACTUAL VEGETATION DYNAMICS.WE PROPOSE TO USE A NEW NETWORK OF TOWER-MOUNTED SOPHISTICATED CAMERAS (INCLUDING TRADITIONAL 3-BAND PHENOCAMS NEWLY DEVELOPED 4-BAND DYNAMIC-RANGE CAMERAS AND TWO HYPERSPECTRAL IMAGING SYSTEMS PAIRED WITH NEW CHLOROPHYLL FLUORESCENCE SPECTROMETERS) TO PROVIDE NOVEL AND RIGOROUS TESTS OF A RANGE OF SATELLITE-BASED APPROACHES INCLUDING TRADITIONAL MODIS STUDIES AND NEWER SOLAR-INDUCED CHLOROPHYLL FLUORESCENCE PRODUCTS FROM GOSAT AND OCO-2. WE WILL COMBINE THESE OBSERVATIONS WITH SOPHISTICATED 3-D CANOPY RADIATIVE TRANSFER MODELING OF CANOPY PHOTOSYNTHESIS REFLECTANCE AND FLUORESCENCE TO REPRESENT THE MECHANISMS OF PHENOLOGY AND PHOTOSYNTHETIC SEASONALITY DETECTABLE BY SATELLITES. THE OVERALL OBJECTIVE OF THE PROJECT IS TO GUIDE IMPROVEMENTS IN OUR UNDERSTANDING OF TROPICAL FOREST PHOTOSYNTHESIS BY COLLECTING AND INTEGRATING A SUITE OF OBSERVATIONS AND MODELING TO (1) TEST HYPOTHESIZED ECOLOGICAL MECHANISMS DRIVING PHOTOSYNTHETIC SEASONALITY (2) SCALE FROM LEAVES TO CANOPY WITH HYPERSPECTRAL CAMERAS THAT CAN ALSO TEST SUN-SENSOR GEOMETRY (BRDF) EFFECTS AND (3) USE TESTED MODELING PRODUCTS TO DISCERN AMAZON FOREST RESPONSES TO THE LARGE-SCALE 2015/2016 EL NINO DROUGHT EVENT.THE PROJECT WILL PROVIDE AN EXTENSIVE SUITE OF NEW AND UNIQUE DATASETS THAT ENABLE US TO FILL THROUGH ADVANCED MODELING TECHNIQUES AND ANALYSIS CRITICAL KNOWLEDGE GAPS IN CURRENT UNDERSTANDING OF WHAT CONTROLS THE RESPONSE OF CANOPY PHOTOSYNTHESIS AND RELATED FUNCTIONS IN AMAZONIAN FORESTS TO SEASONAL VARIATION IN CLIMATE. FOUR MAJOR TYPES OF DATASETS AND DATA PRODUCTS WILL BE DELIVERED: (1) TIME-SERIES OBSERVATIONS OF LEAF-TO-CROWN SCALE FOREST REFLECTANCE PROPERTIES AND ATMOSPHERIC RADIATION FROM TWO INNOVATIVE GROUND BASED IMAGING SENSORS (RESPECTIVELY THE HYPERSPECTRAL VEGETATION IMAGING SYSTEM AND THE HIGH DYNAMIC RANGE ALL-SKY IMAGING SYSTEM) (2) ASSOCIATED HYPERSPECTRAL REFLECTANCE (400-1000NM) IMAGES OF THE CANOPY SURFACE AND VISIBLE INTERIOR COLLECTED AT MULTIPLE VIEW ANGLES TO ENABLE RIGOROUS TESTS OF CANOPY SUN-ANGLE EFFECTS; (3) ASSOCIATED CANOPY-SCALE SOLAR-INDUCED FLUORESCENCE OBSERVATIONS TO COMPARE TO NEW SATELLITE FLUORESCENCE OBSERVATIONS SUCH AS FROM GOSAT AND OCO-2 AND (4) RESULTS FROM STATE-OF-THE-ART MODELING OF 3-DIMENSIONAL CANOPY PROCESSES FOR RADIATIVE TRANSFER AND PHOTOSYNTHESIS THAT INTEGRATE AND LINK OUR OBSERVATIONS FROM LEAVES TO LANDSCAPES OBSERVABLE FROM SPACE TO TROPICAL FOREST PROCESSES. THESE DATA PRODUCTS AND THE IMPROVED KNOWLEDGE WE ACHIEVE WITH THEM WILL CONTRIBUTE TO TESTING AND IMPROVING THE TREATMENT OF TROPICAL FOREST PROCESSES IN ESMS AND HENCE TO IMPROVED PREDICTIONS OF FOREST RESPONSE TO LONG-TERM CLIMATE CHANGE.