Differential Code Biases (DCBs) are the systematic errors, or biases, between two Global Navigation Satellite System (GNSS) code observations at the same or different frequencies. DCBs are required for code-based positioning of GNSS receivers, extracting ionosphere total electron content (TEC), and other applications. Proper knowledge of DCBs is crucial to many navigation applications but also non-navigation applications such as ionospheric analysis and time transfer. With all of the new signals offered by modernized and new GNSS constellations, analysts now require a comprehensive multi-GNSS DCB product.

As part of the International GNSS Service (IGS)  Multi-GNSS Experiment (MGEX) two different DCB products are determined by two analysis groups: Institute of Geodesy and Geophysics (IGG) of the Chinese Academy of Sciences (CAS) in Wuhan and the Deutsche Forschungsanstalt für Luftund Raumfahrt (DLR) in Germany. These files are archived at NASA's Crustal Dynamics Data Information System (CDDIS).

The satellite and station biases computed by the IGG CAS are generated on a daily basis with a latency of 2-3 days and made available in daily BSX files. The constellations and signals analyzed by the IGG CAS are:

Reference: Wang N., Yuan Y., Li Z., Montenbruck O., Tan B. (2016) Determination of differential code biases with multi-GNSS observations, Journal of Geodesy, Vol. 90, No. 3, pp. 209-228, DOI 10.1007/s00190-015-0867-4

The DLR product is updated on a 3-monthly basis and comprises weekly averages of the satellite biases. In addition a full set of daily satellite and station biases is provided for reference purposes and trend analyses. The constellations and signals analyzed by the DLR are:

Reference: Montenbruck O., Hauschild A., Steigenberger P. (2014), Differential Code Bias Estimation using Multi-GNSS Observations and Global Ionosphere Maps, Navigation - Journal of the ION, Vol. 61, No. 3, pp. 191-201, DOI 10.1002/navi.64

Data Format

The IGG CAS DCBs are provided in a preliminary version of the Bias SINEX (BSX) format whereas DLR used the Version 1.00 of February 2016 until Q4/2016 and the Version 1.00 of December 2016 starting with Q1/2017. The December 2016 version of the Bias SINEX format uses a 4-digit year number whereas the version of February 2016 uses a 2-digit year number for specifying the validity intervals.

• Bias SINEX 0.01
• Bias SINEX 1.00 (February 2016)
• Bias SINEX 1.00 (December 2016)

File Naming

The DCB file names

• CAS0MGXRAP_YYYYDDD0000_01D_01D_DCB.BSX.gz
• DLR0MGXFIN_YYYY0010000_NNU_07D_DCB.BSX.gz
• DLR0MGXFIN_YYYY0010000_NNU_01D_DCB.BSX.gz

are based on a new naming scheme proposed for future MGEX products, which is inherited from the new RINEX3 file naming convention; the full specification is given as

AAAVPPPTTT_YYYYDDDHHMM_LEN_SMP_CNT.FMT[.?*]

where: