Estimating chlorophyll concentrations in the optically complex waters of the North Aegean Sea from field and satellite ocean colour measurements
2015
In the Aegean Sea and Eastern Mediterranean there are large discrepancies between in situ and satellite ocean colour
derived chlorophyll concentrations. The quantity that is monitored by ocean colour satellites and that can be used in the
estimation of chlorophyll concentration is the remote sensing reflectance, defined as the ratio of the water leaving
spectral radiance to the downwelling spectral irradiance. It can be determined in the field, with either above or in-water
radiance and irradiance measurements. The complex optical properties of the North-East Aegean Sea, including radiance
and irradiance, were studied during the AegeanMarTech project. Chlorophyll concentration estimates were derived from
simultaneous above and in-water radiometric measurements. These were validated against chlorophyll concentration
field data and compared against concurrent MODIS data from which chlorophyll was derived using two simple empirical
algorithms. It was found that the MedOC3 algorithm outperforms the operational OC3M-547 algorithm and produces the
least bias when compared against HPLC derived in situ chlorophyll. It is concluded that the greatest uncertainty in the
inversion arises due to CDOM absorption below the 488 nm band. The reflectance ratios indicated that there is always an
excess of yellow matter present in the study area and the water type could not be characterized optically as ‘’typical open
ocean” Case 1.
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