Ionospheric TEC Correction for VLBI Based on GNSS Density Network

Very long baseline interferometry（VLBI）is one of the key technologies for orbit determination of Chang'-E satellites in China's lunar exploration project. Ionospheric delay is one of the main errors of VLBI orbit determination. The ionospheric delay correction method based on GNSS inversion is given, which is used in the Chinese VLBI Network. Because there are few stations of international GNSS service（IGS）in China, in order to meet the demand of lunar exploration, more stations are will be builtin China and a new global ionospheric correction model（SHAO）is constructed. Compared with the CODE model, the maximum difference of ionospheric delay Root Mean Square Error（RMSE）on CVN stations is 1.23 ns during the ionospheric quiescence. During the active period of the ionosphere, the maximum difference of the ionospheric delay RMSE on CVN station is 16.80 ns. When the ionosphere is active, the VLBI orbit determination residual based on the SHAO model increases from 6.07 ns to 3.33 ns in S1 band, 9.10 ns to 7.07 ns in S2 band, 0.70 ns to 0.60 ns in X0 band compared with CODE model.