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Harmonizing Landsat-Sentinel-2 data for turbidity mapping in Mississippi Sound
Proceedings of the 2023 Mississippi Water Resources Conference

Year: 2023 Authors: Martins V., Sparks E., Aires U.R. V. ., Rogers A., Doan L.

Satellite imaging systems have been widely used to support water quality and quantity management as it allows water quality analysis using empirical and semi-analytical relationship between optically active constituents (e.g., sediments, chlorophyll-a, dissolved organic matter) and spectral water reflectance. NASA Landsat 8/9 OLI and ESA Sentinel-2 MSI are the most relevant medium spatial resolution data sources for water applications, and the data harmonization from both optical sensors into a single data set, a so-called "virtual constellation", creates an unpreceded opportunity with a repeat frequency of ~ 3 days on average, and higher probability to obtain a cloud-free mapping of water constituents than Landsat or Sentinel-2 alone. This study developed a harmonized Landsat-Sentinel-2 framework for turbidity retrieval in Mississippi Sound. Standard top-of-atmosphere Landsat 8/9 OLI and Sentinel 2A/B MSI imagery were acquired with cloud cover lower than 50%, and both imagery were integrated in the same tile grid area. Cloud and shadow pixels were derived from Fmask algorithm and filtered as no data. We applied "Dark Spectrum Fitting" approach for atmospheric correction, and satellite-based water reflectance was used to model the water turbidity with USGS turbidity records on the Mississippi Gulf coast. The mapping results illustrate the complex freshwater inflow along the Mississippi Sound caused by Bonnet Carré Spillway openings, located about 28 miles northwest of New Orleans, and highlight the abrupt water quality changes in the oyster habitat. We showed the satellite observations are useful to complement the spatiotemporal analysis of recent water quality changes in the coastal region.

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