Developing A New Index for the Detection of Optically Shallow Waters in Complex Coastal Areas from Multi-Spectral Satellite Images Using Radiative Transfer Modelling

Titelangaben

Arabi, Behnaz ; Moradi, Masoud ; Samimi, Cyrus ; Verhoef, Wouter ; Zandler, Harald:
Developing A New Index for the Detection of Optically Shallow Waters in Complex Coastal Areas from Multi-Spectral Satellite Images Using Radiative Transfer Modelling.
2023
Veranstaltung: AGU 23 , 11-15 December 2023 , San Francisco, CA & Online.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung , Vortrag )

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Abstract

Accurate and continuous monitoring of Water Constituent Concentrations (WCCs), including Chlorophyll-a (Chla), Suspended Particulate Matter (SPM), and Colored Dissolved Organic Matter (CDOM), is crucial for the sustainability and well-being of coastal ecosystems. Monitoring of complex shallow coastal waters using remote sensing observations has encountered challenges due to the contamination of recorded energy at the satellite level caused by the sea-bottom effect. This interference compromises the accuracy of generated WCC maps, potentially leading to misleading information in optically shallow waters (OSWs). In this research, for the first time, we introduce a straightforward and robust index that readily distinguishes between OSWs and Optically Deep Waters (ODWs) using multispectral satellite images in complex shallow regions. To define this index, we initially simulated water leaving reflectance values (Rrs) for various combinations of Chla concentration [mg m-3], SPM concentration [g m-3], CDOM absorption at 410nm [m-1], Bottom Albedos, and Water Depth Variables using the Radiative Transfer (RT) Model of the Water-Sea-Bottom (Arabi et al., (2020)). In this regard, we identified the most sensitive wavelengths (i.e., 750nm, 810nm, and 900nm) for the bottom effect contribution in Rrs values and established the index. Next, we evaluated the effectiveness of the proposed index in distinguishing between OSWs and ODWs using satellite images obtained from the Ocean and Land Colour Instrument (OLCI) onboard Sentinel-3, as well as the Medium Resolution Imaging Spectrometer (MERIS) onboard ENVISAT. These images were captured over the complex shallow waters of the Dutch Wadden Sea (DWS), the Netherlands. The proposed index can be served as an intermediate approach to mask out OSWs from various multispectral or hyperspectral satellite images worldwide, eliminating the need for ancillary data such as bathymetry maps. Masking out OSWs from satellite images substantially improves the reliability of the resulting WCC maps for coastal waters. These enhanced WCC maps offer essential information for coastal planners, governmental organizations, and policymakers, facilitating the improvement of maintenance and conservation efforts in coastal regions.