For realistic simulations of the atmosphere-sea-ice-ocean interaction in polar regions, maps of the sea-ice concentration of up to one kilometer resolution are needed. In the present paper, an algorithm is described, which is able to derive such maps based on satellite data from MODIS (Moderate Resolution Imaging Spectroradiometer). This algorithm first retrieves sea-ice concentration for each scene from the satellite-sensed surface temperature. Then, data from multiple satellite overpasses within one day are combined to a map of the sea-ice concentration. The remaining gaps are finally filled in by a scheme considering the brightness temperatures in the gap areas. The results are compared to operational sea-ice concentration products based on SSM/I (special sensor microwave imager) and good agreement is found when averaging MODIS-based data to the same resolution.