The 3D CEMBS (3D Coupled Ecosystem Model of the Baltic Sea) is a coupled ecosystem model of the Baltic Sea. In operational mode it computes 48-h forecasts of the hydrodynamic and biochemical parameters describing the Baltic Sea state. The Cressman assimilation scheme was implemented as part of the system in order to improve overall model accuracy. The system uses satellite-measured sea surface temperature from the MODIS Aqua spectroradiometer for the assimilation process. The satellite measured SST is obtained from a predefined server, which is part of the Satellite Monitoring of the Baltic Sea Environment project (SatBałtyk). To validate the model results and the impact of assimilation on the model's accuracy, two separate test runs were performed using historical data covering the years 2011 and 2012. Independent computations were performed for the model with and without satellite SST assimilation, respectively referred to in this paper as 3D CEMBS_A and 3D CEMBS. The results of the computations were then compared with satellite and in situ measured data to validate the model and the assimilation scheme's implementation. The objective of this paper is to describe the implementation of the satellite SST data assimilation algorithm and to present the results of the preliminary validation of the models with observations.