V. Relationships Between Bio-Optical Parameters of the Black Sea Waters and Spectral Reflectance Coefficient in Spring 2019

The paper presents an analysis of field measurements of the spectral reflectance of the Black Sea and the bio-optical and colorimetric characteristics calculated from it, as well as chlorophyll concentrations and the Secchi disk depth. For the regions of the Black Sea with different characteristics, the averaged values of the calculated characteristics are presented: the effective and dominant wavelength in the reflectance spectrum, the purity of the water color. Using the previously developed bio-optical algorithm, the concentration of chlorophyll, absorption by dissolved organic matter, backscattering by suspended matter, and the vertical light attenuation coefficient were calculated.Inverse relationships are established between the Secchi disk depth and the maximum reflectance, as well as between the Secchi disk depth and the dominant wavelength. Linear relationships with high correlation coefficients are obtained between the surface chlorophyll concentration and the effective and dominant wavelength. A significant relationship was also established between the surface chlorophyll concentration and the maximum reflectance. Among the relationships between bio-optical and colorimetric parameters, a high correlation is observed between the vertical light attenuation coefficient and color purity.Chlorophyll concentrations calculated from the data of the spectral reflectance coefficient using a semi-analytical algorithm are in good agreement with the data of field measurements. Comparison of calculated and measured chlorophyll concentrations with satellite products of optical ocean color scanners shows an overestimation of chlorophyll concentrations by satellite data processing algorithms. The obtained correlations can be used in the future to assess bio-optical parameters in the northern part of the Black Sea.