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Orbits and Clocks for the IGS are generated in three modes (Ultras, Rapids and Finals) from two different processing chains (Ultras and Finals).

GNSS Orbit and Clock Ultra-rapid Processing

Ultra-rapid processing occurs automatically 4 times a day. This process produces both the Ultra and the Rapid ESA products for the IGS.

Since February 2010 also the Rapid and Ultra-rapid products have become true GNSS products. The generation of Rapid and Ultra-rapid GNSS products has been driven by the fact that firstly the density and timeliness of the GNSS stations in the IGS tracking network has increased to a level that allows precise orbit determination of all GNSS satellites in near real time. Secondly, it was driven by significant customer interest. The effect of the improvements of the IGS GNSS tracking network on the quality of our GNSS final orbits is shown in the first figure below . Over the last years there is a significant improvement of the GLONASS orbits , which is caused solely by the improvements in the IGS GNSS tracking network. The GPS orbits are not affected.

The figure below shows the effect of ambiguity resolution and the inclusion of GLONASS on the orbits of the GPS- and GLONASS satellites. Note that only GPS ambiguities are integer resolved. The significant improvements thanks to integer ambiguity resolution on the GPS orbits is clearly visible, on the GLONASS orbits no effect is visible. The figure further demonstrates that there is no negative effect on the GPS orbits due to the inclusion of the GLONASS satellites.

The Navigation Support Office runs in an automated task the production of GNSS orbits and clocks for the IGS.

GNSS Orbit and Clock Final Processing

The Final processing is run once a night with a four day delay, thus ensuring that the maximum number of IGS stations have delivered their Daily RINEX files.

The processing uses 110 stations, with a preference for selecting active GNSS stations from the ITRF2008 reference frame stations in the IGS.

The Navigation Support Office Final solution for the IGS is regularly amongst the top two solutions when compared to the combined IGS Final solution as shown in this plot from the IGS Analysis Center Coordinator (pink curve):