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Apalachicola Bay Research Paper

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2. Methods and Materials 2.1 Study Area Apalachicola Bay is wide estuarine system located in Florida panhandle and covers an area about 539 km2 (Figure-1). The bay is relatively shallow with an average depth of 3.0 m. It is one of the most productive natural systems in North America and highly recognized by the state, federal and international organizations for its pristine water quality and unaffected estuarine habitats (ANERR, 2008). Apalachicola bay and its barrier islands were formed by deltaic processes of Apalachicola River, which is one the unpolluted alluvial system left in the United States. The bay is surrounded by four barrier islands, St. Vincent Island, Little St. George Island, St. George Island and Dog Island. The water exchange…show more content…
The major part of at-sensor radiance is mainly contributed by the atmosphere (aerosols and water vapor), specular reflection of directly transmitted sunlight from the water surface (sun glint), direct reflected radiance from the water surface (sky light) and radiance reflected from whitecaps. The raw at-sensor radiance images were corrected for atmospheric effects using the ENVI v 5.2 (ITT Visual Information Solutions, Inc.) FLAASH (Fast Line of sight Atmospheric Analysis of Spectral Hypercubus) module. FLAASH converts radiometrically-calibrated at-sensor radiance images to surface reflectance images by incorporating the MODTRAN4 radiative transfer code. Landsat-5 TM top-of-atmosphere (TOA) radiance files were converted to FLAASH-compatible units (mW/cm2/sr/nm) by multiplying a scale factor of 0.1. The sensor and flight information, such as sensor type, acquisition date and time, sensor altitude and spatial resolution, were entered manually for each image. This information was supplied with the Landsat L1T product as a separate metadata file (*MTL.txt). The atmospheric model was selected based the observed air temperature during the time of image acquisition. All of the images were corrected for adjacency effects and processed using the DISORT (Discrete Ordinates Radiative Transfer Program for a Multi-Layered…show more content…
The validation analysis was made at AERONET WAVECIS (CSI-6) site, since that is the only ocean color site in the Gulf of Mexico. As AERONET station is located to the south of Terrebonne bay and close to the Mississippi River delta, we assumed that it should represent turbid water environment, at least during the Mississippi River flood condition. 19 clear sky Landsat images (100% clear sky image with no sun glint) are acquired over the AERONET station between 2011 and 2014. They included 5 Landsat-5 TM images, 8 Landsat-7 ETM+ images and 6 Landsat-8 OLI images. There are two ways to evaluate the validity of FLAASH corrected satellite observations, 1) by comparing Aerosol optical thickness (AOT) or horizontal visibility and 2) by relating surface reflectance (ρ) or water leaving radiance (Lw). In processing, Aerosol optical thickness (AOT) was obtained first just before & after the satellite overpass time and averaged to keep comparison closer to satellite measurement. MODTRAN4 code in ENVI-FLAASH is not freely available and therefore Although MODTRAN4 code in ENVI-FLAASH calculates AOT (550 nm) using image data and historical climatology, it does not provide AOT as an output product. However, FLAASH do provide horizontal visibility which can be approximately
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