Estimation of absolute vertical total electron content in the ionosphere from GLONASS / GPS data

When determining absolute ionospheric vertical total electron content (TEC) using pseudo range and phase measurements from GLONASS/GPS data, the systematic error occurs. It is caused by the time difference between passing signals of L1 and L2 ranges in radio-frequency paths of the receiver and satellite (differential code bias, DCB). DCB of 1 ns results in TEC estimation error of ~2.9 TECU. The algorithm for estimating the absolute vertical TEC and DCB is given, and the results of their computation are presented.