THE FRACTION OF PHOTO-SYNTHETICALLY AVAILABLE RADIATION ABSORBED BY PHYTOPLANKTON APAR IS AN IMPORTANT PARAMETER FOR BIOLOGICAL AND ECOLOGICAL STUDIES. IT CONTROLS PHYTOPLANKTON GROWTH AND ULTIMATELY REGULATES THE COMPOSITION AND EVOLUTION OF MARINE ECOSYSTEMS. THERE IS A NEED FOR A GLOBAL LONG-TERM CONSISTENT APAR TIME SERIES TO UNDERSTAND BIOGEOCHEMICAL CYCLES OF CARBON NUTRIENTS AND OXYGEN AND TO ADDRESS IMPORTANT CLIMATE AND GLOBAL CHANGE ISSUES SUCH AS THE FATE OF ANTHROPOGENIC ATMOSPHERIC CARBON DIOXIDE. IN VIEW OF THIS THE PROPOSAL OVERALL OBJECTIVE IS TO DEVELOP SCIENCE QUALITY LEVEL 2 AND LEVEL 3 APAR PRODUCTS FROM MODIS AND VIIRS DATA. THE LEVEL 2 PRODUCT WILL BE INSTANTANEOUS APAR AT THE TIME OF SATELLITE OVERPASS AND AT THE SAME RESOLUTION AS THE LEVEL 1 DATA (I.E. ABOUT 1 KM RESOLUTION) AND THE LEVEL 3 PRODUCTS WILL BE OBTAINED BY BINNING THE LEVEL 2 DATA ONTO A 4.64 EQUAL AREA GRID OVER 1 DAY 8 DAYS A MONTH AND A YEAR (AS DONE FOR OTHER OCEAN COLOR PRODUCTS). ALL THE PRODUCTS WILL HAVE ASSOCIATED UNCERTAINTIES FOR EACH PIXEL/BIN. TO REALIZE THIS OBJECTIVE AN ALGORITHM WILL BE DEVELOPED TO ESTIMATE APAR FROM WATER REFLECTANCE AFTER ATMOSPHERIC CORRECTION. INSTEAD OF USING CHLOROPHYLL CONCENTRATION OR ABSORPTION COEFFICIENTS WHICH ARE ALL ESTIMATED FROM WATER REFLECTANCE VIA EMPIRICAL RELATIONS OR INVERSION SCHEMES I.E. THE APAR ALGORITHM WILL USE WATER REFLECTANCE OR MORE EXACTLY THE RATIO OF IRRADIANCE REFLECTANCE JUST BELOW THE SURFACE NORMALIZED BY THE PURE SEAWATER VALUE DIRECTLY IN AN OPTIMUM MULTI-LINEAR COMBINATION. THIS OPTIMUM COMBINATION WILL BE OBTAINED BY SYSTEMATICALLY EXAMINING THE STATISTICAL PERFORMANCE OF POSSIBLE COMBINATIONS (BASED ON AVAILABLE SPECTRAL BANDS) ON A REALISTIC ENSEMBLE OF APAR AND ASSOCIATED (NOISY AND NOT NOISY) MULTI-SPECTRAL WATER REFLECTANCE. UNCERTAINTY METRICS WILL BE GENERATED FOR PRE-DETERMINED WATER CLASSES USING ESTIMATED AND PRESCRIBED APAR DATA SETS. THEN FUZZY MEMBERSHIP TO THE CLASSES WILL BE USED TO CALCULATE THE APAR UNCERTAINTY FOR EACH PIXEL. THE ALGORITHM WILL BE APPLIED TO MODIS AND VIIRS IMAGERY AND EVALUATED AGAINST IN SITU MEASUREMENTS. A COMPLETE PROCESSING LINE WITH CODE AND ATBD WILL BE DEVELOPED AND DELIVERED TO THE ODPS AT NASA GSFC FOR IMPLEMENTATION TESTING AND GENERATION OF APAR PRODUCTS. THE PROPOSAL DIRECTLY RESPONDS TO THE SOLICITATION UNDER SUB-ELEMENT 2.2 ALGORITHMS NEW DATA PRODUCTS. THE APAR PRODUCTS WILL BE INVALUABLE FOR PRIMARY PRODUCTION AND CARBON EXPORT MODELING. SINCE APAR WILL BE DIRECTLY ESTIMATED FROM WATER REFLECTANCE ERRORS INTRODUCED BY USING VARIABLES DERIVED FROM WATER REFLECTANCE WILL BE AVOIDED AND PRIMARY PRODUCTION ESTIMATES WILL LIKELY BE MORE ACCURATE. THIS WOULD LEAD TO IMPROVED ASSESSMENTS OF SPATIAL VARIATIONS AND TEMPORAL TRENDS OF PRIMARY PRODUCTION IN BASIN SCALES FROM THE MORE THAN A DECADE OF MODIS AND VIIRS MEASUREMENTS. NOTE THAT THE METHODOLOGY CAN BE APPLIED TO GENERATE APAR PRODUCTS FOR OTHER PAST PRESENT AND FUTURE SENSORS IN PARTICULAR THE PLANNED OCI. THE CONTRIBUTION OF THE PROJECT TO UNDERSTANDING THE ROLE OF THE OCEANS IN CARBON CYCLING AND CLIMATE CHANGE ONE OF NASA OBJECTIVES IN EARTH SCIENCE RESEARCH IS EXPECTED TO BE VERY SIGNIFICANT.