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Minutes of the EPN Analysis Centres Workshop (online, November 03-07, 2022)

Thursday, November 03, 2022 - 09:00-12:00 CET (virtual Zoom meeting)

Workshop Programme

Minutes

  1. The GeoForschungsZentrum (GFZ), Germany, became a new EPN analysis centre. GFZ AC will contribute to the EPN with operational final and repro3 solutions. The network of EPN stations to be processed by GFZ AC has already been chosen and consists of 114 stations. GFZ AC will provide initial solutions for testing purposes to the Analysis Centres Coordinator and Troposphere Coordinator in November
  2. It was noted that the International GNSS Service (IGS) published a new reference frame (IGS20/igs20.atx) that will be used for the generation of IGS products (IGSMAIL-8238). IGS will switch from the IGb14/igs14.atx to the IGS20/igs20.atx framework and repro3 standards with the start of GPS week 2238, November 27, 2022 (IGSMAIL-8256). The IGS repro3 standards include, e.g.:
    1. the usage of Galileo observations (in addition to GPS and GLONASS)
    2. the correction of ground antenna misalignments from true north
    3. the usage of latest generation ocean tide loading model (like FES2014b)
    4. adoption of a new secular pole model
    5. new filename convention for the IGS products (details are documented in: http://acc.igs.org/repro3/Long_Product_Filenames_v1.0.pdf)
    Since EPN follows IGS standards, the EPN analysis centres will also move to the IGS20/igs20.atx reference frame and IGS repro3 standards at the same time as IGS.
  3. The details concerning the update from the IGb14 to IGS 20 and IGS repro3 standards were presented by Rolf Dach (CODE AC). The conventional models for mean and high-frequency pole were updated in CODE repro3 analysis. Also, receiver antenna misalignment towards north was considered; the usage of GPS receiver antenna phase centre corrections for other systems was not allowed. Consequently, the signals from other satellite systems without appropriate antenna corrections (PCO and PCV) were eliminated in the analysis. The implementation of new standards in Bernese GNSS Software for versions 5.4 and 5.2 was also shown (some new features, e.g., new secular pole model are not available in version 5.2). The troposphere model VMF3 will be used for troposphere delays modelling in CODE IGS20 operational solutions, while in IGS-Repro3 the VMF1 was used. All CODE IGS20 operational products (final, rapid, ultra-rapid) will cover three systems: GPS, GLONASS and Galileo. All operational products will be provided with new long filenames. For testing purposes, products with new long filenames will be available in a dedicated directory (CODE_TEST) at the AIUB ftp server before the switch to the IGS20.
  4. The IGS20/ITRF2020 reference frame was compared with the latest EUREF cumulative solution (C2220) by Juliette Legrand, the EUREF Reference Frame Coordinator. The characteristic of IGS20 was presented in terms of available stations, discontinuities. In comparison with the IGb14, 21 new stations are available in IGS20 and 8 stations were removed. For 43 stations there are different discontinuities in IGS20 as compared to the EPN discontinuity list. Differences of station positions and velocities between C2220 and IGS20 were also shown. For positions significant offsets in the north (2.8 mm on average) and vertical (-3.9 mm) component were noticed.
  5. The report on the troposphere operational product was presented by Rosa Pacione, the EPN Troposphere Coordinator. The Integrated Water Vapor (computed on the basis of the combined tropospheric zenith total delay) has been included in the EPN combined troposphere product since GPS week 2139. The need for the EPN combined rapid troposphere product was indicated. EPN ACs providing rapid coordinate solutions were therefore asked to provide also troposphere parameters estimated during their rapid data processing. It is also recommended that by GPS week 2238 EPN ACs will start providing troposphere parameters in the SINEX_TRO version 2.00 format.
  6. The EPN analysis centres shall use GPS, GLONASS and Galileo observations for the generation of the EPN products expressed in the IGS20 reference frame. Therefore, it would be mandatory to use consistent IGS products (GNSS orbits, satellite clocks) regarding the mentioned three satellite systems. Presently not all but a number of IGS ACs (e.g., CODE, GFZ) provide the consistent three-system (GPS, GLONASS and Galileo) products.
     
    Currently, EPN ACs including Galileo observations in final solutions use CODE rapid products for data analysis. From GPS week 2238 onwards, it is mandatory to use final IGS AC products that include all three GNSS systems (e.g., CODE and GFZ) to perform the final EPN analysis.
  7. With the switch to the IGS20/igs20.atx framework, the antenna model used in EPN analysis will change. In particular, the presently used receiver antenna model in EPN consists of individual antenna calibrations (epnc_14.atx) complemented by type-mean antenna calibrations from the IGS model (igs14.atx). From GPS week 2238 onwards, the antenna model used in EPN will be almost exclusively based on the new IGS model (igs20.atx). In some exceptional cases, however, individual multi-GNSS antenna calibrations will be also allowed. The individual calibration exceptions could be allowed, e.g., if the calibration for a given antenna-radome pair is not available in the igs20.atx model. However, for the high consistency of future EPN position solutions with global IGS solutions, it would be preferred that individual calibrations would not be accepted for antennas installed at stations included in IGS20 solutions (operational and repro3). Presently, individual calibrations were accepted for LEIAR25.R3_BEVA antenna installed at two Austrian stations (SBG200AUT and TRF200AUT). The new EPN antenna model will be maintained by the Military University of Technology, Poland. The MUT took over this task from the EPN Central Bureau (ROB) who has maintained the EPN antenna model since 2006. Presently, the new model files (epnc_20.atx, epn_20.atx) are available from the MUT server at: http://gnss.wat.edu.pl/euref/station/general/, but will be also available from the EPN CB server. There is also the possibility that the new igs20.atx will be updated before the actual analysis can begin. In this way, for example, the antenna of the type “TPSCR.G5_NONE” (so far only GPS and GLONASS corrections in the igs20.atx) could be replaced by a new calibration of this antenna carried out at Geo++ for all systems. Alternatively, these corrections could be inserted into the new correction files maintained by MUT.
  8. The receiver antenna misalignments from true north are going to be corrected in EPN analysis (operational and repro3). Presently, at 12 EPN stations antennas are not aligned to the North.
     
    The correction of EPN station log files regarding incorrect values for antenna alignments to true north was also discussed. The EUREF mail (no. 11208) was sent on October 13 asking EPN stations managers to report cases for which the antenna misalignment is not correctly documented in the station log file. The correction of station log files at this time might not be desirable for IGS20 stations or EPN stations included in the IGS repro3 solutions since inconsistencies may show up between EPN and IGS solutions. On the other hand, the correction of station log files is reasonable because they would reflect the actual situation at the station. Also, future analysis of GNSS data from affected stations would be based on correct values. The other possibility would be to correct the values of the antenna alignment in log files, but not to use these values in EPN analysis; in EPN analysis the values consistent with the IGS repro3 would be used instead. Further discussion on this topic and conclusions were postponed.
  9. It is recommended that starting with GPS week 2238 the FE2014b ocean tide loading model will be used in EPN analysis in place of the presently used FES2004 model. The BLQ file with FES2014b ocean tide loading parameters for station displacements is available from the EPN CB ftp server.
  10. The usage of the atmospheric tidal loading model is no longer recommended in EPN analysis. The present accuracy of existing models is not satisfactory; the differences between the different models can be at the level of computed corrections. The usage of atmospheric tidal model would be allowed only when an AC is interested in applying an atmospheric non-tidal loading model in its analysis. In this case, however, the AC has to eliminate the atmospheric non-tidal corrections from the computed solutions before submitting them to the EPN.
  11. The update from the VMF1 to VMF3 model and mapping functions for the troposphere modelling in the EPN analysis was briefly discussed. VMF3 is a refined and more accurate version of VMF1; it is also provided with a greater spatial resolution. The VMF3 will be used in operational analysis of the CODE IGS analysis centre (VMF1 was used in CODE repro3 analysis). It is known that there are no significant differences in positions computed using both mapping functions. The usage of VMF3 could be considered in EPN operational analysis.
  12. Following the new IGS filename convention, new filenames were proposed also for EPN AC products from GPS week 2238 onward:
    1. final daily position solutions:
      AAA0OPSFIN_YYYYDDD0000_01D_01D_SOL.SNX.gz
      AAA0OPSFIN_YYYYDDD0000_01D_01D_SUM.SUM.gz
    2. troposphere estimates:
      AAA0OPSFIN_YYYYDDD0000_01D_01H_TRO.TRO.gz
    3. final weekly solutions:
      AAA0OPSFIN_YYYYDDD0000_07D_07D_SOL.SNX.gz
      AAA0OPSFIN_YYYYDDD0000_07D_07D_SUM.SUM.gz
    4. rapid daily solutions:
      AAA0OPSRAP_YYYYDDD0000_01D_01D_SOL.SNX.gz
      where: AAA means an EPN analysis centre acronym (e.g., ASI, BEK, BEV, …), 0 – is a product version (can be increased, e.g., for resubmitted solutions), OPS denotes operational solutions for the campaign/project specification [PPP], FIN – final solutions, RAP – rapid solutions for the solution type identifier [TTT], YYYYDDD0000 is a start date of used observations (YYYY – year, DDD – day of year). The next field is a product length (01D, 07D), followed by a product resolution (01H, 01D, 07D). The last two fields mean the file content (SOL, TRO, SUM) and format (SNX, TRO, SUM).
    5. for near-real time solutions the following format could be used:
      AAA0OPSNRT_YYYYDDDHH00_LEN_RES_SOL.SNX.gz
      where: YYYYDDDHH00 is the start date of the last observation hour used in analysis (not the start date of used observations). The product length (LEN) and its resolution (RES) might be different for each AC.
      All product files should be compressed with the gzip utlility.
  13. The EPN data centres at the BKG and BEV have already prepared the necessary procedures to accept the EPN products submitted with the new long filenames.
  14. Analysis centres are requested to start preparing for the transition to the IGS20 reference framework and the IGS Repro3 standards, so that from GPS week 2238 onwards, all types of solutions offered (final, fast, real-time) will have these standards implemented.
     
    It was confirmed that the the latest versions of software packages (Bernese GNSS Software, GAMIT, GipsyX) used by the EPN ACs are compliant with the new IGS repro3 standards. Since the new version of the Bernese GNSS software (5.4) was released recently, the majority of EPN ACs still use the previous version of the software (5.2) in which some new models and features consistent with IGS standards are not available. It is therefore highly recommended that ACs upgrade their software to the latest version of Bernese GNSS Software (5.4) for the complete consistency with the new IGS standards.
     
    From week 2238 onwards, all IGS products will be provided with long filenames. Presently IGS analysis centres provide test solutions (for weeks 2222-2237) in IGS20 and with long filenames. The products are available at ftp://igs-rf.ign.fr/pub/test_20/WWWW/ and https://cddis.nasa.gov/archive/gnss/products/WWWW/igs20/. In addition, all CODE products with new names are available at: ftp://ftp.aiub.unibe.ch/CODE_TEST. EPN ACs are asked to use these products for testing and preparation of downloading procedures.
     
    EPN ACs are also asked to start providing their rapid and near-real time products with new names for testing purposes before week 2238. These products could be generated according to the new IGS standards, or the present products (in IGb14) could be submitted with new names.
  15. It was also noted that the Guidelines for EPN analysis centres need to be updated to be consistent with the IGS20 reference frame and IGS repro 3 standards. The EPN ACC will start preparing a draft version of the new guidelines and will circulate it to the ACs for comments and further changes.

Monday, November 07, 2022 - 09:00-12:00 CET (EPN-Repro3 - virtual Zoom meeting)

Workshop Programme

Minutes

The EPN-Repro3 workshop took place on 7. November 2022, a few days after the Analysis Centre workshop. Although they were two different workshops, the content to be discussed overlapped in many areas. Therefore, the following report should also be read in conjunction with the minutes of the AC workshop.

The workshop started with a total of seven presentations by Christof Völksen (Introduction to EPN- Repro3: Tasks and Objectives), Benjamin Männel (GNSS analysis at GFZ), Joaquin Zurutuza (EPND research: towards a full harmonization with the National Realizations), Andrzej Araszkiewicz (Impact of mixing antenna calibrations - lesson from EPN-Repro2), Rosa Pacione (EPN-Repro3 Troposphere Products), Juliette Legrand (Status of the EPN historical Database), Tomasz Liwosz (Analysis centres network design and coordinate products in the context of EPN-Repro3), and finally by a discussion round in the end. Based on the topics of the presentations, it can be seen that a sharp separation between the topics of the AC workshops and the repro workshop could not be maintained. This is due to the fact that the speakers were not available on both days of the workshops. It is intended that the slides of the presentations will be available on the website https://www.epncb.oma.be/.

General consideration

EPN-Repro3 should be consistent with the future operational EPN solutions and products analyzed in IGS20. Therefore, the analysis strategy for operational products and repro products should be largely identical. At the same time, EPN-repro3 should also be consistent with IGS repro3. Both conditions can largely be met, but there will also be exceptions. The analysis will be based on the observation data of GPS, GLONASS and Galileo. The AC are asked to provide daily products only.

Reconfiguration of subnetworks

Today, the EPN network is analyzed by 16 ACs. With the participation of the GFZ, a total of 17 ACs will share this task. As things stand today, 12 ACs will participate in EPN-Repro3. In order for each GNSS station to be analyzed by at least three ACs, a reconfiguration of the networks is necessary. The following characteristics have been considered to enable an optimal allocation of the stations: number of stations in the respective networks, region of interest, number of IGS20 stations, and the number of stations that have been revised since 1996. The EPN Analysis Coordinator (Tomasz Liwosz) proposes to assign the following stations to the respective reprocessing ACs.

AC # Sites Stadions
BEK 1 LAMP00ITA
BKG 3 GRAC00FRA, IZMI00TUR, RVNE00UKR
IGE 5 DOUR00BEL, FRNE00ITA, HERS00GBR, SART00ITA, ZIM200CHE
MUT 8 DNMU00UKR, GWWL00POL, ISRN00ITA, KLNK00BLR, MOGI00BLR, SMLA00UKR, SWKI00POL, VITR00BLR
ROB 3 GRAS00FRA, WTZR00DEU, ZIMM00CHE
SGO 13 BISK00CZE, BRTS00BLR, BSVZ00ITA, DGOR00MNE, DVCN00SVK, ENZA00ITA, KNJA00SRB, MNSK00BLR, MOP200SVK, MOPI00SVK, PFA300AUT, RIVO00ITA, VIRG00ITA
SUT 17 AGRN00ITA, BME100HUN, BUTE00HUN, CFRM00CZE, CLIB00CZE, CPAR00CZE, CTAB00CZE, GALH00ITA, GOP600CZE, KATO00POL, KRA100POL, LINZ00AUT, PENC00HUN, SVLL00ITA, UBEN00ITA, VACO00CZE, ZZON00HUN
UPA 15 AGRN00ITA, ASIR00ITA, BIRG00ITA, BSVZ00ITA, GOPE00CZE, GRAZ00AUT, LIGN00ITA, MATG00ITA, MEDI00ITA, PENC00HUN, SART00ITA, SVLL00ITA, UBEN00ITA, UCAG00ITA, VIRG00ITA
WUT 9 BBYS00SVK, KUNZ00CZE, MARP00UKR, NOVP00BLR, PINS00BLR, PSTV00BLR, SODA00FIN, TREU00ITA, TRMI00ITA

The new GFZ network will consist of 114 EPN-stations that will be identical for the reprocessing and the operational analysis.

Antenna PCO and PCV

The antenna correction model (igsR3_2077.atx) used in IGS repro3 is based on new satellite antenna corrections and new receiver antenna corrections. The satellite antenna corrections for Galileo were provided by the European Union Agency for the Space Programme (EUSPA) and showed in connection with multifrequency calibrations from the robot (Geo++) and anechoic chamber (Bonn) a good agreement in scale with the other space techniques. Therefore, the Z-offsets of GPS and GLONASS have been adjusted to maintain this scale. In IGS repro3 it has been decided that if corrections for a specific frequency are not available, these observations are not to be used in the reprocessing. It is therefore proposed to exclude observations from the analysis for which no corrections are available.

For EPN-Repro3, as with the operational EPN analysis, the correction of the antennas will be based on IGS20.atx. The same exceptions for some antenna calibrations will be made in the reprocessing activities as it is discussed during the AC workshop. Nevertheless, while IGS20.atx will expand in the coming years, e.g. by calibrating new antennas and possibly replacing calibrations, the antenna corrections used for EPN-Repro3 may not change further. At a certain point in time before the start of reprocessing the data, the status of the corrections must be fixed and shall not change over time. It might be advisable to assign a certain name for this antenna correction file and make it available through the EPN Central Bureau and MUT.

Products to be used

Each AC can use the reprocessed products for its analysis that are most suitable for their software. Since the observations from GPS, GLONAS and Galileo are to be evaluated, it is advisable to choose an orbit and ERP product that includes these three satellite systems (like ESA, GFZ, COD etc.).

Analysis strategy

The analysis strategy for EPN-Repro3 is oriented to the new operational analysis performed after GPS week 2238 and the analysis strategy used during IGS repro3. It is recommended that users of the Bernese software switch to the new version 5.4 to exploit all the options that are required for the reprocessing.

Troposphere

It was emphasized by the EPN Troposphere Coordinator (Rosa Pacione) that each station should be represented at least three times in the subnetworks of the EPN in order to achieve reliable results. The tropospheric products are to be estimated with a resolution of one hour, which is usually completely sufficient. The hourly values should refer to the middle of the hour and not to the full hour, so that the linking of the daily data is easier to achieve. Rolf Dach, however, had concerns about the representation of the tropospheric parameters at half hour with the Bernese: Due to the piecewise linear parameterization of the BSW solutions, the nodal points for the troposphere are in the full hours. One must therefore transform from 25 nodal points to 24 offset intervals, which is not a 1:1 transformation. This would mean (at least mathematically) that one would have to transform to 24 offsets and shifts including 23 continuity conditions.

Data shall be provided in the SINEX_TRO version 2.0. It is advisable that bad data is eliminated in advance and not included in the analysis.

Products names

The products file names shall be defined according to the new definition for long product names as it is documented in http://acc.igs.org/repro3/Long_Product_Filenames_v1.0.pdf. See also the minutes of the AC workshop 2022. The basic product file name is given by:

AAAVPPPTTT_YYYYDDDHHMM_LEN_SMP_CNT.FMT[.gz]

In order to distinguish operational products from reprocessed products, the IGS proposes the abbreviation R03 for the third reprocessing campaign. To further differentiate between IGS reprocessed products and EUREF regional reprocessed products, the abbreviation E03 is proposed for the EPN network. This results in a name (using the AC GFZ as an example) for a daily reprocessed SINEX solution of doy 214 in 2021:

GFZ0E03FIN_20212140000_01D_01D_SOL.SNX[.gz]

EUREF Station Information file

In the past years, the EPN Central Office has continuously provided updated information on the changes in the EPN station setup via the EUREF station information file in BERNESE format. Most analysis centres have become accustomed to this service and would probably like to be able to continue using it. This would be very helpful and would make the work of the other ACs much easier. At the same time, this ensures that all ACs refer to the same information.

Update (it has been decided after the workshop): This service will now be maintained by WUT (Tomasz Liwosz), but it is supposed that the EUREF station information file will be available through the EPNCB.

Open Questions

At the end of the meeting, time was running out and not all points could be discussed conclusively. It was therefore agreed to compile, together with the minutes, a list of remaining questions that need to be answered before reprocessing activities can begin. Some of the open questions are also related to the operational and perhaps also to the RAPID analysis of the EPN. This is indicated by an “x” in the following table.

Topic Operational/Rapid Repro
VMF1 of VMF3:
While in IGS repro3 the Vienna Mapping Function (VMF1) was used throughout, with VMF3 a new improved function is available that allows a higher spatial resolution. So far it is possible to use the new VMF3 for the operational solution of the EPN. The goal for the reprocessing is, that EPN-Repro3 should be consistent with both IGS repro3 and the new operational solutions. If the upcoming operational EPN analyses in IGS20 refer to VMF3, then EPN-Repro3 will no longer be consistent with either IGS repro3 or EPN, depending on the choice of the corresponding mapping function in repro3 analyses. Probably VMF1 is recommended for the reprocessing of the EPN because consistent VMF3 grids are not available for the entire period of interest. 		x x
ATM:
Questions concerning the use of atmospheric tidal models (ATL) is not finally resolved for the reprocessing. The use of the atmospheric tidal loading model is no longer recommended for the upcoming EPN analysis in IGS20. The reason is the unsatisfactory accuracy of the existing models. In order to be consistent with the upcoming operational solutions of the EPN, it is also recommended to dispense the use of ATL. Also, in IGS repro3 ATL corrections were not applied. 		- x
Antenna correction models:
The ACs of the EPN hope that a least one more antenna will be included in the IGS20.atx file maintained by AIUB. In case that the file will not be updated a decision is required if those antenna corrections will be included into the file provided by MUT. 		x x
Antenna Orientation:
The correction of ground antenna misalignments from true north will be performed for the operational and repro3 solution in the IGS20. In IGS repro3 this misalignment was also corrected. For some IGS stations antenna misalignments were recently reported that are not documented in station log files. Since these cases were not considered in IGS repro3, a decision on the treatment of these cases in EPN operational and repro3 analysis has to be made. 		x x
Elimination of Observation due to missing correction models:
While BERNESE is capable to remove observation with missing antenna correction models it is requested to check with GFZ (EPOS), MUT (GAMIT) and ASI (ASI) if they can handle this problem in the same manner.		 x x
Benchmark/Testing:
Proposal for a test period by comparing the reprocessed products with the new operational products. It is conceivable that data will be generated in reprocessing set-up for a few weeks starting from GPS-Week 2238. This allows the comparison of the products and a fine tuning. 		- x
Schedule Reprocessing:
EPN-Repro3 should only be launched when all questions regarding analysis and standards have been clarified. Initially, all ACs should concentrate their work on the operational and rapid solutions. Only then should EPN-Repro3 be started. Nevertheless, the work should be carried out quickly thereafter. As not all ACs have the same capacity to carry out EPN-Repro3, the pace of analysis is likely to vary. The effort should not be underestimated, as almost data from the last 27 years (GPS-week 834-2237) has to be evaluated. 		- x