[IGSMAIL-8248] IGS Repro3 orbit. clock, bias and attitude solutions available [SEC=OFFICIAL]

Salim Masoumi Salim.Masoumi at ga.gov.au
Fri Sep 2 23:13:03 UTC 2022



Dear Colleagues,



The combined orbit, clock and observable-specific bias products along with the computed satellite attitudes from the 3rd IGS reprocessing campaign (Repro3) are now available for the period 1994-2020 in the weekly sub-directories at https://cddis.nasa.gov/archive/gnss/products/repro3/ and will soon be available at ftp://igs.ign.fr/pub/repro3, with the files prefixed "IGS2R03FIN", indicating version 2 of the combinations which used AC and satellite weighting for the orbit combinations. These products are consistent with the SINEX solutions prefixed "IGS1R03FIN", and are aligned to the IGSR3 reference frame, as described in [IGSMAIL-8026]<https://lists.igs.org/pipermail/igsmail/2021/008022.html>, [IGSMAIL-8044], and https://igs.org/acc/reprocessing/#repro3.



While the orbit combinations were performed by the IGS Analysis Centre Coordinator (IGS ACC) at Geoscience Australia, the clock and bias combinations were performed at Wuhan University led by Professor Jianghui Geng, who is currently the IGS PPP-AR Working Group Chair. Also, the reference attitudes were computed by Dr. Sebastian Strasser from Graz University of Technology. I would like to thank both for their huge efforts in this campaign. I would also like to thank Dr. Simon Banville, former chair of the IGS PPP-AR Working Group, who provided a lot of insightful advice and analyses to validate the products.



I would also like to take this opportunity to thank all the IGS Analysis Centres for their high-quality contributions to the Repro3 campaign and their ongoing efforts. Details of the contributing IGS Analysis Centres are available in the IGS Technical Report 2021<https://files.igs.org/pub/resource/pubs/2021_techreport.pdf>: Chapter 2: Analysis Centers: Analysis Center Coordinator: Table 5. The report also contains brief information about the combination procedures, which were also presented at Tour de l'IGS: 1st Stop: Repro3<https://igs.org/tour-de-ligs/presentations#1st-stop-presentations>.



The available products, and some of the new features of the products and combination strategy since Repro2 are listed below. For any further information, please feel free to contact acc at igs.org<mailto:acc at igs.org>.



Kind Regards,

Salim Masoumi





AVAILABLE PRODUCTS

------------------



* daily combined orbit solutions:              IGS2R03FIN_${yyyy}${doy}0000_01D_05M_ORB.SP3               1994-01-02 to 2020-12-31

* daily combined clock solutions:              IGS2R03FIN_${yyyy}${doy}0000_01D_30S_CLK.CLK               1995-01-01 to 2020-12-31

* daily combined bias solutions:                IGS2R03FIN_${yyyy}${doy}0000_01D_01D_OSB.BIA               2000-01-01 to 2020-12-31

* daily reference satellite attitude:           IGS2R03FIN_${yyyy}${doy}0000_01D_30S_ATT.OBX               1994-01-02 to 2020-12-31

* daily orbit combination summaries:      IGS2R03FIN_${yyyy}${doy}0000_01D_01D_SUM.SUM               1994-01-02 to 2020-12-31

* --- in JSON format:                              IGS2R03FIN_${yyyy}${doy}0000_01D_01D_SUM.JSON    1994-01-02 to 2020-12-31
* daily clock combination summaries:     IGS2R03FIN_${yyyy}${doy}0000_01D_01D_CLS.CLS           1995-01-01 to 2020-12-31
* --- in JSON format:                              IGS2R03FIN_${yyyy}${doy}0000_01D_01D_CLS.JSON       1995-01-01 to 2020-12-31
* weekly EOP combination summaries:   IGS2R03FIN_${yyyy}${doy}0000_07D_01D_EOP.JSON     1995-01-16 to 2020-12-26
                   (in JSON format)
* weekly combination summaries:           IGS2R03FIN_${yyyy}${doy}0000_07D_01D_SUM.SUM     1994-01-02 to 2020-12-26


where ${yyyy} stands for the 4-character year and ${doy} for the 3-character day-of-year.



Just as the changes made to the style of the traditional SINEX summary files as indicated in [IGSMAIL-8026]<https://lists.igs.org/pipermail/igsmail/2021/008022.html>, I have made changes to the style of the summary files, as well as the addition of the daily orbit combination summaries, and the addition of the summaries in machine-readable JSON format.



SOME NEW FEATURES OF THE COMBINED PRODUCTS SINCE REPRO2

---------------------------------------------------

* Repro3 combined products include GPS, GALILEO and GLONASS information. While GPS information starts from 1994-01-02, the GLONASS information starts from 2002-01-01, and the GALILEO starts from 2013-01-01.



* Since the start of the year 2000, the "integer" clock combinations and the phase biases allow for PPP with ambiguity resolution. The clocks prior to the year 2000 were performed similar to legacy clock combination since no bias combination was performed prior to 2000 due to lack of AC bias solutions.




COMBINATION STRATEGY

-------------------

* The orbit combinations were performed by a newly developed combination software by the IGS ACC at Geoscience Australia. The new software is, however, written based on the same robust weighted average algorithm as the IGS ACC legacy software, with minor differences to allow for the multi-GNSS combinations, with the main difference being in weighting of the ACs: while the legacy GPS-only combinations use an AC-specific weighting for doing the combinations, the Repro3 orbit combinations are weighted based on AC and satellite, meaning that each AC may receive a different weight for each satellite. In the orbit comparisons and PPP validations, this proved to have insignificant impact on the results when compared to the legacy combinations, but was found useful to isolate the impact of "badly behaved" satellites on the combinations.



* The satellite attitudes were calculated using the GROOPS software developed at Graz University of Technology, following the algorithms described here<https://graz.pure.elsevier.com/en/publications/reprocessing-multiple-gnss-constellations-and-a-global-station-ne>.



* The clock and bias combinations were performed by the PRIDE ckcom software developed at Wuhan University. Some of the main features of the Repro3 clock combinations and differences compared to the IGS ACC legacy clock combinations are as below:



* For the Repro3 and using the ckcom clock combination software, the phase biases are combined in conjunction with the clocks, which combines them into clocks with integer characteristics. This allows for the use of the clocks and biases for PPP with ambiguity resolution. This is a new feature for the IGS combined clocks.



* As an improvement compared to the legacy clock combinations, the Repro3 clock combinations implement the satellite-PCO and attitude corrections to the AC solutions, which improves the clock consistencies among ACs and the accuracy of the combined clocks.



* A set of common satellites among all ACs are selected which are present at all epochs, and the alignment of the clock datum is then performed epoch by epoch.



* As with the previous Repro2, the combined clocks are aligned to GPST by fitting a linear model to the GPS broadcast ephemeris. The clocks are not re-aligned to the IGST; therefore, the combined clocks will have sizable day boundary discontinuities.







Salim Masoumi PhD |  A/g GNSS Team Leader
GNSS Analysis Section  |  Positioning Australia Branch

Space Division



t +61 2 6249 9688    ga.gov.au<https://www.ga.gov.au/>



<https://www.ga.gov.au/>



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