Abstract
Multispectral and hyperspectral sensor data of the bio-optical parameters with a high spatial resolution are important for monitoring and mapping of the coastal ecosystems and estuarine areas, such as the Kneiss Islands in the Gulf of Gabes. Sentinel 2 S2A and Hyperion Earth observing-1 (EO1) imaging sensors reflectance data have been used for water quality determination and mapping of turbidity TU and chlorophyll Chl-a in shallow waters. First, we applied a tidal swing area mask based on uncorrelated pixel via 2D scatter plot between 665 nm and 865 nm to eliminate the overestimation of the concentration of water quality parameters due to the effect of the bottom reflection. The processing for mapping and validating Chl-a, Turbidity S2A, and EO1 were performed using a relation between reflectance bands and in situ measurements. Therefore, we were able to validate the performance of the case 2 regional coast colour processor (C2RCC) as well as our region-adapted empirical optical remote sensing algorithms. Turbidity was mapped based on the reflectance of 550 nm band for EO1 (R2 = 0.63) and 665 nm band for S2A (R2 = 0.70). Chlorophyll was mapped based on (457/528 nm) reflectance ratio (R2 = 0.57) for EO1 and (705/665 nm) reflectance ratio (R2 = 0.72) for the S2A.
Highlights
Sentinel 2 Sentinel 2A (S2A) and Hyperion Earth observing-1 (EO1) imaging sensors reflectance data have been used for water quality determination and mapping of turbidity TU and chlorophyll chlorophyll a (Chl-a) in shallow waters
The semi-analytical, empirical bio-optical models, band ratio or chlorophyll quantification algorithms have been developed mainly according to the concentration range of in situ Chl-a and turbidity and in terms of the specific wavelengths available in the multi or hyperspectral sensors (MODIS, SeaWiFS, EO1, MERIS, SENTINEL, etc.) [9]-[17]
The spectral responses of these different depths clearly show that a shallow waters mask coinciding with areas of swaying tide must be applied at the time of the satellite overpass
Summary
Hyperspectral imaging and empirical relationships between reflectances obtained by optical remote sensing algorithms have been used to assess water quality [2] [3] [4] [5] [6], allowing chlorophyll a (Chl-a) and turbidity TU mapping in shallow waters. The assessment of suspended matter relies on field spectrometry data merged with the satellite data and is obtained from a combination of channels at several wavelengths [18] or a single wavelength algorithm [19] These applications are suitable for the coastal or estuarine areas at a coarse spatial resolution (250 m - 1000 m). Landsat or SPOT data have been used to retrieve case II water’s optical properties [16] [20]
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