Discrepancies Between Provided DCB Estimates and Equivalent Formulations in CAS DCB Product

摘要

In order to obtain meaningful absolute Total Electron Content (TEC) estimates using Global Navigation Satellite System (GNSS) measurements it is essential to correct the Differential Code Bias (DCB) induced by the satellite and receiver hardware. Estimates of the satellite DCBs may be obtained from products provided by a number of agencies, including the multi-GNSS experiment (MGEX) of the International GNSS Service (IGS). MGEX provides two different DCB products, one produced by the Institute of Geodesy and Geophysics (IGG) of the Chinese Academy of Sciences (CAS) and the other produced by the German Space Operations Center (DLR). Both of these products provide DCBs between a few defined pairs of signals. In some cases the provided pairs must be combined to form the DCB in which the user is interested. For example, the DCB between Global Positioning System (GPS) L1C/A and the L2C pilot channel must be obtained using the following combination of DCB estimates C1C-C2W + C2W-C2L from either the CAS or DLR product. However, using the CAS product the same DCB can also be obtained using the combination C1C-C1W + C1W-C2W + C2W-C2L. There are also multiple ways to obtain the bias between GPS L1C/A and L2P(Y) (Z-tracking) and GLObal NAvigation Satellite System (GLONASS) L1C/A and L2C/A using the CAS product. Regardless of the combination used the final DCB should be the same as it is between the same two signals, however, this is not always the case. For a few satellites both methods produce the same results, but for others the difference can exceed one nanosecond, which translates to more than 2TECu when estimating TEC. This paper illustrates these differences between CAS DCB combinations over a year (October 1, 2017 to October 1, 2018).