PHOTOSYNTHETICALLY AVAILABLE RADIATION (PAR) AT THE OCEAN SURFACE 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 ACCURATE AND CONSISTENT PAR 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 AND THE LIMITATIONS OF CURRENT PAR PRODUCTS FROM SENSORS IN POLAR ORBIT (DO NOT CAPTURE CLOUDINESS DIURNAL CHANGES) THE PROPOSAL OVERALL OBJECTIVE IS TO DEVELOP A SCIENCE QUALITY STANDARD OCEAN SURFACE PAR PRODUCT FROM DSCOVR EPIC DATA. THE PRODUCT WILL BE A TIME SERIES OF GLOBAL IMAGERY OF DAILY MEAN PAR REACHING THE OCEAN SURFACE AND ASSOCIATED UNCERTAINTY (BIAS STANDARD DEVIATION) IN EQUIRECTANGULAR AND EQUAL-AREA SINUSOIDAL PROJECTIONS (18.4 KM RESOLUTION AT THE EQUATOR AND 20 KM RESOLUTION RESPECTIVELY). SPECIFIC OBJECTIVES ARE: (1) TO MODIFY/ADAPT THE CURRENT NASA OBPG PAR ALGORITHM TO EPIC DATA (2) TO QUANTIFY THEORETICAL PERFORMANCE (3) TO ASSOCIATE UNCERTAINTIES TO EPIC PAR ESTIMATES ON A PIXEL-BY-PIXEL BASIS (4) TO CREATE AND IMPLEMENT A FULL EPIC PAR PROCESSING LINE (5) TO APPLY THE ALGORITHM TO ACTUAL EPIC IMAGERY AND GENERATE A SEVERAL-YEAR EPIC PAR TIME SERIES (6) TO COMPARE THE EPIC PAR ESTIMATES WITH THOSE FROM CONCURRENT SATELLITE SENSORS (I.E. MODIS AND VIIRS) AND (7) TO EVALUATE THE EPIC PAR ESTIMATES AGAINST IN SITU MEASUREMENTS. THE ALGORITHM DEVELOPMENT TASKS INCLUDE REMAPPING THE HOURLY DATA TO A COMMON GRID INTEGRATING ATMOSPHERIC FUNCTIONS SPECTRALLY AND TEMPORALLY DURING THE DAY ELIMINATING DATA CONTAMINATED BY SUN GLINT INCORPORATING ANCILLARY INFORMATION SUCH AS OZONE CONTENT SEA ICE EXTENT (FOR MASKING) AND AEROSOL OPTICAL PROPERTIES. THEORETICAL PERFORMANCE WILL BE ASSESSED USING SIMULATIONS OF THE EPIC REFLECTANCE AND CORRESPONDING DAILY MEAN PAR. UNCERTAINTIES WILL BE ASSIGNED AS A FUNCTION OF CLEAR SKY DAILY MEAN PAR AND CLOUD FACTOR. THE FULL PROCESSING LINE WILL BE APPLIED TO GENERATE EPIC DAILY PAR IMAGERY FROM LEVEL 1B DATA AVAILABLE DURING THE 3-YEAR PROJECT I.E. SINCE MARCH 2015 (AT LEAST 5 YEARS). EVALUATION AGAINST IN SITU MEASUREMENTS WILL BE MADE AT VARIOUS OPEN OCEAN SITES (FIXED PLATFORMS AND MOORED BUOYS) AND IN COMPARISONS WITH OTHER SATELLITE ESTIMATES INCLUDING FROM SENSORS OPERATING AT GEOSTATIONARY ALTITUDE. THE COMPARISON OF EPIC PAR ESTIMATES AND MODIS AND VIIRS PAR ESTIMATES WILL QUANTIFY BIASES (GEOGRAPHICALLY AND TEMPORALLY DEPENDENT) ENABLING CONSISTENCY ACROSS SENSORS. THE INVESTIGATION WILL PROVIDE AN ALGORITHM AND A COMPLETE PROCESSING LINE WITH ATBD TO GENERATE FROM THE EPIC OBSERVATIONS A GLOBAL LEVEL 2 OCEAN SURFACE DAILY MEAN PAR PRODUCT WITH UNCERTAINTY SPECIFIED FOR EACH PIXEL DURING THE LIFETIME OF THE DSCOVR MISSION. ACCURACY IS EXPECTED TO BE BETTER THAN THAT OF CURRENT NASA OBPG PAR PRODUCTS DUE TO MULTIPLE OBSERVATIONS DURING DAYTIME AND SPATIAL COVERAGE IMPROVED ESPECIALLY AT LOW AND MIDDLE LATITUDES. THE PROJECT RESPONDS DIRECTLY TO THE NNH18ZDA001NA. 46 SOLICITATION NEW PRODUCT DEVELOPMENT ELEMENT. THE EPIC DAILY MEAN PAR PRODUCT WILL BE INVALUABLE FOR A WIDE RANGE OF RESEARCH APPLICATIONS SUCH AS PRIMARY PRODUCTION AND CARBON EXPORT MODELING ECOSYSTEM DYNAMICS MIXED-LAYER PHYSICS AND PHOTOCHEMICAL TRANSFORMATIONS OF DISSOLVED ORGANIC MATTER. THE GENERATED EPIC PAR TIME SERIES WILL COMPLEMENT EXISTING PAR DATASETS AND HELP TO BRING ABOUT CONSISTENCY ACROSS SENSORS ALLOWING A BETTER DESCRIPTION OF BIOLOGICAL PHENOMENA THAT COULD LEAD TO NEW INFORMATION ABOUT TEMPORAL VARIABILITY OF BIOLOGICAL PROCESSES. THE CONTRIBUTION OF THE PROJECT TO UNDERSTANDING THE ROLE OF THE OCEANS IN CARBON CYCLING AND CLIMATE CHANGE ONE OF NASA S CHIEF OBJECTIVES IN EARTH SCIENCE RESEARCH IS EXPECTED TO BE VERY SIGNIFICANT.