Systematic changing and variations of GPS/GLONASS differential code biases

Along with navigation and precise time applications, Global Navigation Satellite Systems (GNSS) are widely used nowadays to remotely sense the ionosphere in equatorial, mid-latitude and arctic regions. While estimating absolute TEC using the code and phase measurements simultaneously, a satellite and receiver dependent systematic error occurs. This error is associated with differential code biases (DCB) - the different, frequency dependent processing times of L1 and L2 signals in RF paths, both for satellites and receivers. Due to these DCBs, TEC, in some cases, can obtain even non-physical negative values. For example, a 1-ns DCB causes a ∼3 TECU error in TEC estimation.