THIS PROPOSAL SPECIFICALLY TARGETS THE ELEMENT ON TECHNIQUES TO IMPROVE REMOTE SENSING OF WATER QUALITY AND ITS SUB-ELEMENT ON IMPROVING UNDERSTANDING OF THE LINK BETWEEN OPTICAL AND WATER-BODY PROPERTIES . THE PHOTOBLEACHING OF CHROMOPHORIC DISSOLVED ORGANIC MATTER (CDOM) HAS RECEIVED LITTLE ATTENTION AS A FACTOR INFLUENCING WATER QUALITY AND THE REMOTE SENSING OF WATER QUALITY. CDOM IS ONE OF THE MAIN OPTICALLY ACTIVE CONSTITUENTS IN ESTUARINE AND COASTAL WATERS AND IS INTIMATELY CONNECTED TO WATER QUALITY. IT IS A DOMINANT CONTRIBUTOR TO THE ABSORPTION AND ATTENUATION OF UV AND VISIBLE RADIATION AND THEREBY AFFECTS UNDERWATER VISIBILITY AS WELL AS LIGHT AVAILABILITY TO PHYTOPLANKTON. IN COASTAL WATERS CDOM IS OFTEN USED AS A PROXY FOR THE REMOTE SENSING OF DISSOLVED ORGANIC CARBON (DOC) AN IMPORTANT WATER QUALITY INDICATOR AND BIOGEOCHEMICAL VARIABLE. SOLAR EXPOSURE IN SURFACE WATERS INEVITABLY LEADS TO THE PHOTOCHEMICAL DEGRADATION OF CHROMOPHORES AND TO A LOSS OF ABSORPTION IN CDOM A PROCESS CALLED PHOTOBLEACHING. BY AFFECTING THE INHERENT OPTICAL PROPERTIES (IOPS) OF THIS MAJOR OPTICALLY ACTIVE CONSTITUENT OF COASTAL WATERS PHOTOBLEACHING CAN ALTER THE APPARENT OPTICAL PROPERTIES (AOPS) OF THE WATER (E.G. KD OR RRS) THE RELATIONSHIP BETWEEN CDOM AND RELATED BIOGEOCHEMICAL PROPERTIES LIKE DOC AND THE RELATIONSHIPS BETWEEN APPARENT OPTICAL PROPERTIES AND OTHER WATER QUALITY OR BIOGEOCHEMICAL PROPERTIES (E.G. KD CHL-A). EVIDENCE SUGGESTS PHOTOBLEACHING IS A POTENTIALLY IMPORTANT PROCESS IN ESTUARINE AND COASTAL WATERS BUT A THOROUGH QUANTITATIVE ASSESSMENT OF THE MAGNITUDE VARIABILITY AND IMPACTS OF THIS PROCESS IS VERY MUCH LACKING. PHOTOBLEACHING CAN BE EXPECTED TO VARY DEPENDING ON FACTORS SUCH AS INCIDENT SOLAR IRRADIANCE CDOM COMPOSITION/ORIGIN LIGHT EXPOSURE HISTORY VERTICAL UV ATTENUATION VERTICAL MIXING AND MIXED LAYER DEPTH. AS A RESULT THE EFFECTS OF PHOTOBLEACHING CAN BE EXPECTED TO DIFFER GREATLY AMONG COASTAL SYSTEMS AND SEASONS WITH CONSEQUENCES IN COASTAL WATERS FOR THE ACCURACY OF WATER QUALITY RETRIEVALS FROM EMPIRICAL ALGORITHMS (E.G. OC3M KD2M) AND/OR RELATIONSHIPS BETWEEN OPTICAL AND BIOGEOCHEMICAL VARIABLES (CDOM-VS-DOC). THE OVERARCHING HYPOTHESIS OF THE PROPOSED RESEARCH IS THAT CDOM PHOTOBLEACHING HAS A MAJOR INFLUENCE ON THE AOPS OF SURFACE COASTAL WATERS AND THAT THE SPATIO-TEMPORAL VARIATIONS IN PHOTOBLEACHING-INDUCED CHANGES IN IOPS AND AOPS CAN HAVE A SIGNIFICANT IMPACT ON THE ACCURACY OF WATER-QUALITY RETRIEVALS FROM OCEAN COLOR. IN ORDER TO TEST THIS HYPOTHESIS WE PROPOSE TO LEVERAGE TWO LARGE AND IDEAL DATA SETS OF FIELD AND LABORATORY MEASUREMENTS AND RESULTS OF PHOTOCHEMICAL EXPERIMENTS FROM THE NORTHERN GULF OF MEXICO (GULFCARBON PROJECT) AND BEAUFORT SEA (MALINA PROJECT). WE ALSO PROPOSE TO COMPLETE THIS DATA SET WITH NEW DATA AND EXPERIMENTS FROM THE SOUTHERN GULF OF MAINE. WE WILL COMBINE ALL DATA WITH A PHOTOCHEMICAL MODEL OCEAN-COLOR REMOTE SENSING AND HYDROLIGHT SIMULATIONS TO ACHIEVE THE FOLLOWING SEQUENCE OF OBJECTIVES: 1) DEVELOP A LARGE DATA BASE OF PHOTOBLEACHING EFFICIENCIES (APPARENT QUANTUM YIELDS) 2) ESTIMATE REALISTIC CDOM PHOTOBLEACHING RATES ACROSS A RANGE OF CONTRASTING COASTAL WATERS AND SEASONS 3) TO ASSESS THE IMPACTS OF THESE RATES ON THE APPARENT OPTICAL PROPERTIES OF COASTAL WATERS AND 4) TO REUSE THIS INFORMATION TO DEVELOP AN EASILY IMPLEMENTABLE CORRECTION SCHEME TO IMPROVE THE ACCURACY OF STANDARD WATER QUALITY RETRIEVALS FROM REMOTE SENSING OF OCEAN COLOR. FICHOT WILL BE THE P.I. SUPERVISE A GRADUATE STUDENT AND OVERSEE THE ENTIRE PROJECT. THE PROJECT WILL INVOLVE GRADUATE UNDERGRADUATE AND HIGH-SCHOOL STUDENTS IN THE RESEARCH. ALL NEW FIELD AND LABORATORY-BASED MEASUREMENTS WILL BE CARRIED OUT USING NEW AND STATE-OFTHE- ART EQUIPMENT FROM THE PI S LABORATORY AT BOSTON UNIVERSITY