GPS navigation and SAR imaging systems performances depend on correct characterization of perturbations due to electromagnetic wave propagation through turbulent media such as ionosphere or troposphere. At these systems frequencies, ionospheric scintillations, which are more or less important according to geophysical conditions, must be studied as well as mean perturbations due to medium crossing. After a description of ionospheric parameters, existing scintillation models are presented. Then, MPS and MPC numerical phase screens methods developed to simulate time series representative of ionospheric scintillations are described. These methods, which are applicable whatever the temporal and geographical localizations are, evaluate scintillation parameters close to analytical theoretical ones. Several propagation conditions can be simulated such as propagation of a wide band source signal or wave propagation through bidimensional anisotropic screens.