Data on the planetary albedo which were registered in Channel 0.4 - 1.1 mum (VIS) by the geostationary satellite METEOSAT were used to determine a quantitative characteristic of a cloud cover over the Baltic Sea area. By applying the obtained results and the input data generated by the model of the Interdisciplinary Centre for Mathematical and Computational Modelling of the Warsaw University, calculations of irradiance on the sea surface were done using the model of radiation transmission in the Baltic Sea atmosphere. The results were compared to the actinometric data that were continuously recorded by the Gdansk Maritime Institute?s measuring buoy that was anchored at 18?31.094?E and 54?56.157?N. It was noted that the application of ICM model information on the atmosphere to the solar radiation transmission model results in decreasing the calculated irradiance values by approximately 15% in relation to the measured values. If cloud cover data in the input data set are replaced by relevant satellite data, then the average difference between the measured data and the modelled ones decreases to approximately 5%.