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Analysis Activities' Published in the IGS Annual Report 2003/2004 (Gendt, 2005)

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Analysis Activities' Published in the IGS Annual Report 2003/2004 (Gendt, 2005) 2003/2004 Analysis Coordinator Report Gerd Gendt and Thomas Nischan GeoForschungsZentrum Potsdam (GFZ), Department Geodesy & Remote Sensing, Telegrafenberg A17, D-14473 Potsdam, Germany, E-Mail: [email protected] 1 Introduction Similar to the years before this report completes the report 'Analysis Activities' published in the IGS Annual Report 2003/2004 (Gendt, 2005). A summary of the most important changes during 2003/2004 will be presented and the status of the product quality will be given. Many figures summarizing combination statistics on orbits, clocks and Earth Rotation Parameters (ERP) are shown, where most of the plots can be retrieved from the IGS Analysis Coordinator web-page at http://gfz-potsdam.de/igsacc. The IGS Workshop and Symposium held in March 2004 in Bern (Meindl, 2004) passed a series of recommendations, which strived to consolidate and improve the quality of the IGS products. Among them was also the quality monitoring of the Precise Point Positioning (PPP) realization of the ITRF using the IGS Final and Rapid products, which demanded for larger additional activities in the combination process (see Section 7). 2 IGS products – Overview The International GNSS Service is committed to provide the highest quality GPS&GLONASS observation data and products as the standard for global navigation satellite systems (GNSS) in support of scientific activities such as improving and extending the International Terrestrial Reference Frame, monitoring deformations of the solid Earth, variations in the liquid Earth (sea level, ice sheets, etc.) and in Earth rotation, determining orbits of scientific satellites, and monitoring the troposphere and ionosphere. Table 1. Quality of the IGS Products as of December 2004 (for details see http://igscb.jpl.nasa.gov/ components/prods.html) Product IGS Final IGS Rapid IGS Ultra Rapid Adjusted Predicted Updates Weekly Daily 4 times daily 4 times daily Delay ~13 days 17 hours 3 hours Real-time GPS Orbits < 5 cm < 5 cm < 5 cm ~ 10 cm GPS Satellite Clocks < 0.1 ns 0.1 ns ~0.2 ns ~ 5 ns Station Clocks < 0.1 ns 0.1 ns GLONASS Orbits 15 cm Polar Motion /LOD 0.05 mas < 0.1 mas 0.1 mas 0.3 mas LOD 0.02 ms/day 0.03 ms/day 0.03 ms/day 0.06 ms/day Station Coordinates (h/v) 3 mm / 6 mm Ionospheric TEC grid 2-8 TECU 2-9 TECU Troposperic zenith path 4 mm 6 mm delay Table 1 gives an overview of the estimated quality of the IGS products at the end of 2004. With the CODE Analysis Center (AC) there is the first AC that provides combined GNSS – GPS & GLONASS – products (since June 2003). The IGS is generating since several years Ultra Rapid products. The products comprises adjusted solutions (for a 24 hour data part) for orbits, ERPs and clocks, and predictions of those parameters for the next 24 hours. 3 Changes during 2003/2004 – Overview Mid 2003 we had a smooth transition of the Analysis Coordination and the combination for the orbits/clock/ERP to the GeoForschungsZentrum Potsdam. An overview of all combination results and comparisons can be found at http://gfz-potsdam.de/igsacc. The products of two new Analysis Centers, GOPE (Geodetic Observatory Pečny, Prague, Czech Republic) and MIT (Massachusetts Institute of Technology, Cambridge, MA, USA) were successfully validated over several months and are included in the official combination starting in 2004: • GOPE contributes to the Ultra Rapid Products. Having one additional AC the quality and robustness of this IGS product is improved, and, because a minimum of 3 contributing ACs for each satellite is necessary especially the number of missing satellites could be reduced. • MIT contributes to the Final Products. The large network of 150 stations used by MIT significantly improves the maintenance of the IGS network. Having for all of their stations a 5-min clock solution it is a valuable contribution to the IGS Time and Frequency Product. Since March 2004 the clock results generated by the Clock Product Center (see https://goby.nrl.navy.mil/IGStime) are now directly used in all provided products. They provide a much better realization of the IGS time scale (see K. Senior, et al. this Volume). During the combination the raw clock products are submitted to the Clock Product Center and the combination is continued after the new RINEX clock (clk) and clock summary (cls) files are returned. The clocks included in the SP3 files will be taken from the new product, so that the SP3- and clk-files are consistent. The clock differences between all satellites and stations within one epoch are identical with the raw clock combination and therefore the PPP results are not affected. By this change the new clock products can now be downloaded from the IGS global data centers. To get a better inside into the quality of the Ultra Rapid products the adjusted parts of the corresponding AC submissions and of the combined results are validated too. The results are distributed among the ACs in the summary reports for the Rapid and Ultra Rapid products. Since 2004 weekly IGS Reports are distributed to inform the user community about the Ultra Rapid product quality (IGSMAIL#4812). Since April 2004 the Ultra Rapid products are generated every six hours. Since April 2004 CODE is now the second IGS AC, besides JPL, which is providing satellite clocks with a sampling rate of 30 sec. For the generation of a validated combined product still a third AC is missing and therefore all ACs are again requested to consider such a product. Since August 2004 orbit products are provided in SP3-c format. The new format (see ftp://igscb.jpl.nasa.gov/igscb/data/format/sp3c.txt) includes error codes for orbits and clocks per epoch as well as flags of predicted parts (P) in the Ultra Rapid files. The file names have the extension ".sp3c". The new features are especially important for the predicted orbits, where, compared to the other IGS orbit products, a larger variation in the quality exists. For an Table 2. Summary of changes during 2003/2004 GPS week Date Change 1223 2003-06-15 Switch of Rapid and Ultra Rapid Combination to GFZ 1231 2003-08-10 Switch of Final Combination to GFZ 1242 2003-10-26 Addition of the adjusted part of the Ultra Rapid orbits to the product validation 1250 2003-12-21 Distribution of weekly reports on the quality of the Ultra Rapid orbit predictions 1250 2003-12-21 Addition of MIT products to the Final Combination 1252 2004-01-04 Addition of GOPE products to the Ultra Rapid Combination 1253 2004-01-11 Introduction of new terrestrial reference frame realization IGb00 1261 2004-03-21 Products of the Clock Product Center are used in all Rapid and Final products 1267 2004-04-19 Ultra Rapid Combination repeated every 6 hours 1270 2004-05-10 Introduction of PPP validation 1283 2004-08-08 IGS products are distributed in SP3-c format (old format is kept for on overlapping time period) 1300 2004-12-05 Switch of GLONASS Combination to GFZ, name change from igx to igl 1304 2005-01-02 Exclude orbit parts from all products which are not covered by RINEX data from the IGS global network overlapping time period both files, the new and the usual SP3 one (SP3-a format), will be available to allow for a smooth transition. Since the end of 2004 the SP3-products are ‘cleaned’ in the sense that orbit information are removed from the SP3-file after a maneuver (the only exception is that an AC is providing a solution with the flag ‘M’) and for time intervals which are not covered by data; for that purpose the global IGS network is checked. For the GLONASS combination the pilot phase has ended and the official products are offered since December 2004. Three ACs (COD, BKG, ESA) are contributing with analysis of GLONASS microwave data and one (MCC) with the analysis of laser data for 3 satellites. The later solution is used for validation only. All changes are summarized in Table 2. Details of changes not touched yet will be given in Sections 6 and 7. 4 Reference Frame Since the introduction of the terrestrial Reference Frame (RF) IGS00 ("IGS01P37_RS54.snx") in December 2001 the stability of its realization in the Rapid and Ultra Rapid products, where the RF defining stations are fixed, have been significantly improved. Additionally, an enlarged number of stations in the analysis and the ambiguity fixing introduced by some ACs contributed to the stabilization of the Rapid products. Meanwhile, almost a dozen of the RF stations experienced problems and had to be removed from the list. To avoid a further deterioration in the RF realization it was decided to release an update of IGS00 with significantly more sites (~100). The new realization, called IGb00 ("IGS03P33_RS106.snx"), was adopted in 2004 (GPS week 1253). There are no significant transformations between IGS00 and IGb00 (see R. Ferland, this Volume). 5 Atmosphere and Ionosphere Products Since October 2003 the IGS Final ionosphere products are official now and they are distributed by the IGS Global Data Centers (for details see M. Hernandez, this Volume). Since the beginning of 2004 the official IGS Final Tropospheric Products are based on a PPP using the official IGS Final orbits and clocks. The PPP technique allows the generation of this product for all the available stations in the global IGS network and enables also a efficient consistent reprocessing of historical data (at present the new products are available back to 2000; for details see Y. Bar-Sever et al., this Volume). Up to now for an overlapping period the ‘classical’ combined IGS Final Tropospheric Products are still available.
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