THIS PROPOSAL RESPONDS TO THE ROSES A.30 RSWQ FUNDING ANNOUNCEMENT. WE ADDRESS ELEMENT 2.2.2 IMPROVING UNDERSTANDING OF THE LINK BETWEEN OPTICAL AND WATER-BODY PROPERTIES FOR APALACHEE BAY FLORIDA A SEAGRASS-DOMINATED COASTAL REGION OF THE NORTHEAST GULF OF MEXICO WHERE THE WATER COLUMN CHANGES FREQUENTLY BETWEEN OPTICALLY DEEP AND SHALLOW CONDITIONS IN RESPONSE TO RIVER DISCHARGE SEDIMENT RESUSPENSION AND PHYTOPLANKTON BLOOMS. APALACHEE BAY HAS HISTORICALLY SUPPORTED A LARGE AND HIGHLY PRODUCTIVE SEAGRASS COMMUNITY- THE SECOND LARGEST CONTIGUOUS SEAGRASS BED IN THE CONTINENTAL US. HOWEVER SEAGRASSES HAVE UNDERGONE REPEATED CYCLES OF LOSS AND RECOVERY OVER THE PAST THIRTY YEARS WITH AN OVERALL DOWNWARD TREND IN ABUNDANCE. PERSISTENT PHYTOPLANKTON BLOOMS LASTING A YEAR OR MORE DECREASE WATER COLUMN TRANSPARENCY CAUSING LIGHT STRESS AND MORTALITY FOR SEAGRASSES. AT THE ECOSYSTEM LEVEL PRIMARY PRODUCTION SHIFTS FROM SEAGRASSES TO PHYTOPLANKTON DURING THESE CYCLES. THE OBSERVED LONG-TERM DECLINE IN SEAGRASS ABUNDANCE CAN HAVE DEVASTATING IMPACTS THIS ECOSYSTEM AND THE SERVICES IT PROVIDES. APPLICATION OF REMOTE SENSING DATA TO PROTECTION AND MANAGEMENT OF THIS VALUABLE RESOURCE IS LIMITED BY THE COMPLEX RAPIDLY CHANGING CONDITIONS IN THESE SHALLOW COASTAL WATERS. HOWEVER ALTHOUGH NEARSHORE WATERS AND ESTUARIES ARE OPTICALLY COMPLEX THEY ARE MORE ACCESSIBLE THAN MORE HOMOGENEOUS DEEPER WATERS OFFSHORE. AS A RESULT WE HAVE 14 YEARS OF IN SITU DATA WITH WHICH TO TEST DEVELOP AND VALIDATE NEW ALGORITHMS FOR RETRIEVAL OF PHYTOPLANKTON CHLOROPHYLL CDOM AND TURBIDITY WITH THE ULTIMATE GOAL OF CREATING AN OPTICAL MODEL FOR SEAGRASS SURVIVAL AND GROWTH. OUR FIRST TASK IS TO DEVELOP AND VALIDATE STRATEGIES TO RESOLVE WATER COLUMN TRANSPARENCY AND OPTICAL DEPTH. USING NEW SEGMENTING TOOLS BASED ON SPATIAL HETEROGENEITY OF BOTTOM REFLECTANCE WITHIN PIXEL CLUSTERS WE WILL CLASSIFY EACH OF 18 APALACHEE BAY REGIONS WITHIN EACH SATELLITE AS OPTICALLY DEEP OR SHALLOW. WE WILL THEN APPLY AND TEST THE ACCURACY OF EXISTING ALGORITHMS TO EACH REGION IN EACH SCENE BASED ON ITS OPTICAL DEPTH USING 14 YEARS OF IN SITU DATA. WE WILL USE STANDARD DEEPWATER ALGORITHMS AS A BENCHMARK BUT WE ARE ESPECIALLY INTERESTED IN EXPLORING ALGORITHMS LIKE SWIM (MCKINNA ET AL. 2015) AND THOSE OF TZORTZIOU ET AL. (2007) THAT INCORPORATE BENTHIC REFLECTANCE AND HIGHER WAVELENGTHS RESPECTIVELY. ACKNOWLEDGING THE ERRORS ASSOCIATED WITH ATMOSPHERIC CORRECTIONS AND REMOTE SENSING REFLECTANCE (RRS) VALUES FOR BLUE WAVELENGTHS WE WILL USE RAYLEIGH CORRECTED REFLECTANCE VALUES (RRC) FOR OUR ANALYSES. WE WILL RELY PRIMARILY ON MODIS/A IMAGERY FOR OUR ANALYSES BUT WE WILL FILL IN DATA GAPS ESPECIALLY DURING THE SUMMER GROWING SEASON WITH VIIRS SEAWIFS AND SENTINEL-3 IMAGERY. USING OUR VALIDATED ALGORITHMS AND THE LARGEST POSSIBLE IMAGERY DATASET WE WILL HINDCAST ALTERNATING STATES OF SEAGRASS AND PHYTOPLANKTON PRIMARY PRODUCTION FOR THE PERIOD 2003-2016. SEAGRASS PRODUCTION WILL BE ESTIMATED FROM BENTHIC REFLECTANCE UNDER OPTICALLY SHALLOW CONDITIONS COMBINED WITH IN SITU GROWTH MEASUREMENTS. USING OUR TESTED AND IMPROVED ALGORITHMS FOR RETRIEVAL OF WATER COLUMN PROPERTIES WE WILL BUILD A SPATIALLY-EXPLICIT OPTICAL MODEL CALCULATING LIGHT AVAILABLE SEAGRASSES FOR THE PERIOD 2003-2016 AND VALIDATE IT USING IN SITU DATA. THE ULTIMATE GOAL OF THE RESEARCH THE OPTICAL MODEL WILL THEN BE USED TO FORECAST FUTURE CHANGES AND LINK THOSE CHANGES TO ACTIVITIES IN THE ADJACENT WATERSHEDS. CREATING A CONSISTENT ACCURATE AND RICH TIME SERIES OF WATER COLUMN PROPERTIES AND ALTERNATING STATES OF PRIMARY PRODUCTION IN ESTUARINE AND COASTAL WATERS HAS PARTICULAR RELEVANCE TO SEAGRASS RESOURCES AND ECOSYSTEM MANAGEMENT IN APALACHEE BAY AS WELL AS BROADER RELEVANCE FOR ALL COASTAL AREAS.