Variability of GPS/GLONASS differential code biases

While estimating ionospheric total electron content (TEC) using both pseudorange and phase GPS/GLONASS data, there occurs a systematic error caused by the difference in processing times of L1 and L2 signals through radio frequency paths of satellites and receivers, known as differential code biases (DCBs). A 1-ns DCB causes an ∼2.9 TECU error in TEC estimation. Along with systematic DCB variations, seasonal variations, most likely related to variations in the receiver environment (temperature, humidity), also exist for some receivers and can reach in some cases up to ∼20 TECU