Method for Estimating the Diffuse Attenuation Coefficient from the Beam Attenuation Coefficient in the Waters of the Black Sea

The vertical attenuation coefficient of downward irradiance is one of the hydro-optical characteristics that determine the parameters of the light field in the sea. Information from the vertical attenuation coefficient of downward irradiance (or the diffuse attenuation coefficient) is necessary when determining an important biological and ecological parameter of water basin — the thickness of the euphotic layer. A possible method for estimating the vertical attenuation coefficient of downward irradiance (or the diffuse attenuation coefficient) from measurements of the beam attenuation coefficient at a wavelength of 525 nm for the Black Sea waters is described. The Black Sea waters are characterized by an increased content of dissolved organic matter and belong to type II waters (according to the Morel classification). Examples of the application of the method are given, which showed a quite high correlation (R = 0.85) between the values of the vertical attenuation coefficient of downward irradiance determined from in situ measurements of underwater irradiance with a photometer and calculated from in situ measurements of the beam attenuation coefficient with a transparency meter. The standard deviation of the calculated values from the measured ones is 0.008 m –1 , the maximum deviation is 0.023 m –1 .