A calibrated TEC method for inversion of ionospheric GPS occultation data
电离层GPS掩星观测改正TEC反演方法

When the low-Earth orbit (LEO) satellite is low, the contribution of the Total Electron Contents(TEC)above the satellite is not neglectable for inversion of GPS-LEO ionospheric occultation.The exponential extrapolate method which is widely used now may induce a big error, especially when LEO's orbit is lower. We propose an inversion algorithm, calibrated TEC method, to estimate the TEC above LEO using the data from the non-occultation portion of the satellite track. We use the three-dimensional ray-tracing program to simulate the ionospheric occultation. Then we inverse the simulation data by the calibrated TEC method and exponential extrapolate method, and the results are compared with the model values. The results show that, for GPS/MET, the inversion profiles of the extrapolate method and the calibrated TEC method agree with the given model ionosphere, and the calibrated TEC method is better than the extrapolate method at higher altitude. For CHAMP, the errors of extrapolate method are large, and inversion profiles of the calibrated TEC method are consistent with the model values. Then, the calibrated TEC method is applied to the processing of actual GPS/MET ionospheric occultation data, and the inversion profiles are reasonable.These prove that the calibrated TEC method is a good algorithm for inversion of ionospheric GPS occultation,especially when the LEO's orbit is low.