RTS Products

RTS Combination Products

The RTS Combination Product consist of GNSS satellite orbit and clock correction as well as code bias information. In the past IGS RTS correction were formatted according to the RTCM SSR standard for State Space Representation. Because the standard extension for other GNSS beyond GPS and GLONASS is still under development within RTCM, products are provided in the IGS-SSR format. Data streams use the NTRIP protocol. RTS corrected products refer to the International Terrestrial Reference Frame 2020 (ITRF 2020).

The product streams available in the RTS are combination solutions generated by processing individual Real Time solutions from participating Real-time Analysis Centers (RTAC). The effect of combining the different RTAC results is a more reliable and stable performance than that of any single AC’s product. Operational responsibility for the official combination products lies with the IGS Real Time Analysis Center Coordinator (RTACC).

The official products currently include multi-GNSS corrections to the satellite orbits and clocks and code biases.  There are also product streams that provide Real Time combined global ionospheric models (Liu et al. 2021). All product streams are described in more detail below:

• SSRA02IGS1/SSRC02IGS1 (previously IGS02/IGC02): Kalman filter combination produced using BKG’s BNC software. The Kalman filter solution requires a few minutes convergence time to reach full accuracy. Once converged, the accuracy is maintained unless there is a reason to restart the software. A mechanism is in place to avoid publishing results during the convergence period. The orbit information is extracted from one of the incoming AC solutions. In the Kalman Filter approach satellite clocks estimated by individual Analyses Centers (ACs) are used as pseudo-observations within the adjustment process. Each observation is modelled as a linear function of three estimated parameters: AC specific offset, satellite specific offset common to all ACs, and the actual satellite clock correction which represents the result of the combination. These three parameter types differ in their statistical properties. The satellite clock offsets are assumed to be static parameters while AC specific and satellite specific offsets are stochastic parameters with appropriate white noise. The solution is regularized by a set of minimal constraints. A recursive algorithm is used to detect orbit outliers. The largest difference between AC specific and mean satellite positions is computed. If this exceeds a threshold, the corrections of the affiliated AC are ignored for the affected epoch. This product has now transitioned to the official multi-GNSS combination solution, including corrections for GPS, GLONASS and Galileo satellites. The combination is done system-wise for the reference signals as specified in the IGS RTWG and mentioned below.
• SSRA03IGS1/SSRC03IGS1 (previously IGS03/IGC03): Kalman filter combination using BKG’s BNC software (see description for SSRA02IGS1/SSRC02IGS1 above). It is a multi-GNSS product as well, including corrections for GPS, GLONASS, Galileo and BeiDou.
• IONO00IGS1: Real Time combined VTEC Global Ionospheric Model in IGS-SSR format (spherical harmonics to degree 15), with a temporal resolution of 20 minutes. The combination is performed by UPC from solutions provided by a number of Real Time Ionospheric Analysis Centers.
• IONO01IGS1:Real Time combined VTEC Global Ionospheric Model in IGS-SSR format (spherical harmonics to degree 15). The combination is performed by CAS.

References

Liu, Q., Hernández-Pajares, M., Yang, H., Monte-Moreno, E., Roma-Dollase, D., García-Rigo, A., Li, Z., Wang, N., Laurichesse, D., Blot, A., Zhao, Q., Zhang, Q., Hauschild, A., Agrotis, L., Schmitz, M., Wübbena, G., Stürze, A.,  Krankowski, A., Schaer, S., Feltens, J., Komjathy, A.,and Ghoddousi-Fard, R. (2021). The cooperative IGS RT-GIMs: a reliable estimation of the global ionospheric electron content distribution in real time. ESSD, 13 (9), 4567-4582. doi: 10.5194/essd-13-4567-2021