A global ionospheric range error correction model for single frequency GNSS users

Transionospheric navigation and radar systems operating at single frequencies of less than 10 GHz are impacted by ionospheric refraction. Since the ionospheric delay is proportional to the total electron content (TEC) of the ionosphere along the ray path, a user friendly TEC model is helpful in various applications. Thus, a global TEC model (NTCM-GL) has recently been developed in DLR. The basic approach of the model is presented and the performance is discussed in comparison with GNSS single frequency correction models such as the Klobuchar or GPS model and the NeQuick model. The empirical approach describes functions on season, local time, geographic/geomagnetic location and solar irradiance conditions. The solar activity is controlled by the solar radio flux index F10.7. The approach needs only 12 coefficients for describing the main ionospheric features in good quality. The model approach is based on global TEC data provided by the Center for Orbit Determination in Europe (CODE) at the University of Berne over more than half a solar cycle (1998-2007). The model fits to these input data with a negative bias of 0.3 TECU (1 TECU=1x1016m-2) and a RMS deviation of 7.5 TECU. It has been found that the NeQuick and NTCM-GL model show a similar performance which is by a factor of nearly 2 better than the performance of the Klobuchar model at the European sector. Since the coefficients cover a full solar cycle, no updating is required. Hence, NTCM-GL may easily be used as a correction model for single frequency GNSS applications