Minutes of the EPN Analysis Centres Workshop (online, November 03-07, 2022)
Thursday, November 03, 2022 - 09:00-12:00 CET (virtual Zoom meeting)
- Report of EPN Analysis Centres Coordinator: status of EPN coordinate products and preparations for the switch to IGS20, Tomasz Liwosz
- IGS-repro3/IGS20 update, changes w.r.t. IGb14, Rolf Dach
- Comparison of the current EPN Reference Frame Solution (C2220) with ITRF2020/IGS20, Juliette Legrand
- Report of the Troposphere Coordinator: Operational Product, Rosa Pacione
Monday, November 07, 2022 - 09:00-12:00 CET (EPN-Repro3 - virtual Zoom meeting)
- Introduction to EPN-Repro3: Tasks and Objectives, Christof Völksen
- GNSS analysis at GFZ, Benjamin Männel
- EPND research: towards a full harmonization with the National Realizations, Joaquin Zurutuza
- Impact of mixing antenna calibrations - lesson from EPN-Repro2, Andrzej Araszkiewicz
- EPN-Repro3 Troposphere Products, Rosa Pacione
- Status of the EPN Historical Database, Juliette Legrand
- Analysis centres network design and coordinate products in the context of EPN Repro3, Tomasz Liwosz
- Discussion and Summary, Christof Völksen
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/.
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.
|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.).
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.
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.
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:
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:
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.
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.
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.
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.
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.
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.
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.
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.
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.