Figures and Statistics from the IGS Rapid GPS Orbit Combination

Orbit and clock comparison figures

The WRMS plots below (the first two rows) show the Weighted RMS (mm) of the individual AC orbit solutions with respect to the IGS Rapid (IGR) products. The Clock Std Dev and Clock RMS plots show the standard deviations (ps) and RMS (ps) of the individual AC clock solutions with respect to the IGS Final products. The solid lines show weighted ACs and the dashed lines show unweighted solutions as of today.

The clock Std Dev values are computed by removing a separate bias for each satellite/station clock, whereas this is not done for the clock RMS values. In the case where one uses these products with carrier phase data and estimates an ambiguity parameter for each station-satellite pair (i.e. most positioning applications), the satellite clock biases will be absorbed by the ambiguity parameters, so the Std Dev statistics are appropriate measures to assess the consistency of the solutions.

In other applications where no station-satellite bias parameter is estimated or where the underlying satellite time scale itself is of interest, the RMS statistics may be useful. The larger RMS differences between the AC clocks stem from a few different factors. For satellite clocks, these differences mainly come from differences in how the ACs treat differential code biases (DCBs); most of the ACs use similar differential code biases (e.g. those provided by COD); however, when an AC uses a different set of DCBs it can show larger satellite clock RMSs. For the station clock RMS's, differences in the number of stations and the satellites processed can result in differences in the station clock RMS statistics.

Because of the relative nature of clocks, and since the AC clocks are re-aligned before combination, the main statistic to control the quality of the AC clocks is the clock Std Dev (and not the clock RMS).

The clock figures currently show combined satellite and station clock statistics. We are working on displaying separate satellite and station clock statistics for better visual comparisons. These separate statistics are available in the clock summary files (*.CLS.SUM) files. For display purposes, the daily clock Std Dev and RMS values from the Final combination summaries are weekly averaged. For display purposes, the daily clock Std Dev and RMS values from the Final combination summaries are weekly averaged.

On 11 April 2014, this webpage was updated to include following comparisons:

IGR and the observed part (IGA) of the 00h IGS Ultra-rapid product
IGR and the real-time part of the IGS Ultra-rapid product (denoted here as IGU**)
IGR and the IGS Real-time streams (denoted here as IGC**)

Note that IGC** are 24h SP3 files each containing four 6h segments (hours 4 thru 10) from each update interval of the IGS RT streams. The comparison with IGR is done daily over the full 24h of each IGC SP3. IGU** consists of 4 separate comparisons to IGR done each day over the first 6h of each IGS Ultra-rapid product.

The IGS Ultra-rapid orbit prediction errors grow with the sqrt. Each 6h segment within the 24h IGC file has a latency of 4 hours. The WRMS orbit differences between IGU** and IGC** for the first few weeks of this comparison are consistent with the errors for hours 4-10 of the IGS Ultra-rapid orbit predictions.

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WRMS of IGS Rapid orbits (raw) recent weeks GIF PS history GIF PS
WRMS of IGS Rapid orbits (smoothed) recent weeks GIF PS history GIF PS
Std Dev of IGS Rapid clocks recent weeks GIF PS history GIF PS
RMS of IGS Rapid clocks recent weeks GIF PS history GIF PS

ERP comparison figures

The next plots show the difference between individual AC Rapid ERP solutions and the IGS Final product. The differences are shown for X-, and Y-pole, X-, and Y-pole rate, and LOD (length of day).

For the X-, and Y-pole figure the individual series are shifted by 1 mas.
For the X-, and Y-pole rate figure the individual series are shifted by 4 mas/day.
For the LOD figure the individual series are shifted by 0.2 ms/day.

AC Rapid ERP differences w.r.t. IGS Finals

X-Pole recent weeks GIF PS history GIF PS
Y-Pole recent weeks GIF PS history GIF PS
X-Pole Rate recent weeks GIF PS history GIF PS
Y-Pole Rate recent weeks GIF PS history GIF PS
LOD recent weeks GIF PS history GIF PS
IGS Rapid ERP differences w.r.t. IGS Finals recent weeks GIF PS history GIF PS


Orbit transformation results per AC

The next plots show the weekly averages of the Helmert translation, rotation, and scale parameters for the individual AC solutions with respect to the IGS Rapid products.
"igu" is the 24 hours predicted orbit.

Trans. Rot. Trans. Rot.
GIF recent weeks Scale X Y Z X Y Z history Scale X Y Z X Y Z
PS recent weeks Scale X Y Z X Y Z history Scale X Y Z X Y Z


The next plots show the daily Helmert scale, translation, and rotation parameters for the individual AC orbit solutions separately, with respect to the IGS Rapid products.

The translations are shifted by 50 mm. The rotations are shifted by 1 mas.
"igu" is the 24 hours predicted orbit.

Scale/Translations from:

    recent weeks      history
GIF cod emr esa gfz grg jgx jpl ngs sio usn whu igu | cod emr esa gfz grg jgx jpl ngs sio usn whu igu
PS cod emr esa gfz grg jgx jpl ngs sio usn whu igu | cod emr esa gfz grg jgx jpl ngs sio usn whu igu

Rotations from:

GIF cod emr esa gfz grg jgx jpl ngs sio usn whu igu | cod emr esa gfz grg jgx jpl ngs sio usn whu igu
PS cod emr esa gfz grg jgx jpl ngs sio usn whu igu | cod emr esa gfz grg jgx jpl ngs sio usn whu igu


 

24 September 2025, originator IGS ACC