The present work deals with the treatment of ionospheric effects in single and dual frequency GNSS receivers for satellite applications in general and the application of selected ionospheric correction algorithms to Astrium's MosaicGNSS receiver in particular. Currently, the MosaicGNSS receiver provides a 3D position error RMS of 10 m that is supposed to be improved by the ionospheric correction algorithms. For single-frequency applications, three algorithms based on ionospheric models are chosen to be analyzed, i.e. the Lear model, the Klobuchar model and the Montenbruck model. Additionally, the GRAPHIC code / DRVID technique is selected for analysis that uses code and carrier-phase of the L1 signal to calculate the ionospheric path delay. For dual-frequency applications, the ionospheric error is directly calculated by use of P1 and P2 pseudorange measurements. These algorithms are implemented in the MosaicGNSS receiver, tested and finally validated by use of real flight data from the CHAMP mission. Additionally, several data editing techniques are developed that are specifically tailored to exclude invalid or degraded measurements from the navigation solution. By applying a strategy that consists of selecting the ionospheric correction algorithm depending on the long-term solar activity, a 3D position error RMS of 3.45 - 6.63 m can be achieved.