Abstract：In order to eliminate the effect from the topside ionosphere above LEO, it is necessary to retrieve electron density profiles based on the calibrated TEC below LEO, which introduces the approximation that the LEO and GPS orbit are close to being coplanar. In this paper, firstly an improved technique is proposed to eliminate this approximate error based on the noncalibrated TEC, and then the technique is applied in the inversion of simulated data and real observation data respectively. The results show that:1) whether the simulated data or real observation data are used, the inversion results derived from the noncalibrated TEC are better than those derived from the calibrated TEC technique, especially it is more obvious for low LEO altitudes;2) based on the above data, some serious errors occur while the electron density profiles are retrieved from the calibrated TEC, on the contrary, the inversion results derived from noncalibrated TEC are reasonable.
