Direct and indirect determination of the Linke turbidity coefficient

The Linke turbidity coefficient has been measured for the first time in the island of Crete, in the Mediterranean sea. Short time series data were used to calculate the beam irradiance through the global and diffuse irradiance on a horizontal plane. Strong seasonal effects on the monthly averaged TL values are not observed, while their profile displays a smooth transition from lower to higher values. Examination of the daily averages reveals TL values as low as 2.0 and as high as 4.0. The most frequent values of the turbidity are found in the range of 2.3–3.5. Archival global irradiance data from the same site are also used to estimate the turbidity with the aid of a robust estimator and two simple, analytical models. The usefulness of this approach is validated with data from a number of networks registering the solar radiation. The proposed method allows to estimate the turbidity with an rms error of 0.3, using only, good quality, global irradiance data. Large amounts of data can easily be processed with the proposed method.