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by Heinz Habrich, Bundesamt für Kartographie und Geodäsie, Germany

Summary of Discussions/Action Items

The 6^th EPN Local Analysis Centres Workshop was held on October 22-23, 2008 in Frankfurt am Main, Germany, hosted by the Federal Agency for Cartography and Geodesy (BKG). 33 registered workshop participants from 15 European countries visited the workshop and followed the 24 oral presentations. The workshop was organized in 6 working sessions, each with presentations and time for discussion, which was used intensively. The workshop programme is attached to the minutes.

An overview of recent developments of the existing EPN structure and products was given in working session 1 ("Reports from the EPN Coordination Group"). Carine Bruyninx announced a new tool for the compilation of site log-files, which is going to be established at the EPN Central Bureau (EPN CB). It will allow station operators to enter all requested information in dedicated data fields of a web-site and to successively generate the log-file format compliant text file. Heinz Habrich presented a draft comparison of two EPN cumulative solutions, one calculated by Ambrus Kenyeres within the scope of the EPN time series project and one by Heinz Habrich as results from the analysis coordinator. The final results of this initiative will be presented at the Technical Working Group (TWG) meeting on November 3-4, 2008.

10 Local Analysis Centres (LACs) explained in working session 2 ("Local Analysis Centres reports") their current activities and future plans. Bruno Garayt reported on plans of a scientific collaboration on GNSS permanent network analysis with an institution in Algeria (INCT). One of the objectives aims at becoming an EPN LAC, and potentially an AFREF LAC. Some additional contacts are on the way with an institution in Tunisia (OTC).

Rolf Dach summarized in working session3 ("Experiences with new processing strategies") the recent developments and plans of the Bernese Software through a comparison to the already released version 5.0. 14 of in total 16 LACs to compute the EPN products use bernese Software. New features of the software will allow to resolving GLONASS phase ambiguities, to apply modern troposphere mapping functions, e.g. Vienna mapping function or global mapping function, to define validity intervals for station coordinates and much more model changes. The release of the new software is not expected before year 2009 and for that reason new processing options have not been discussed during the workshop.

Ambrus Kenyeres compared in session 4 ("New analysis products") the EPN coordinate time series with a re-processed time series of the EPN network carried out by WUT/MUT and ROB. Beside other improvements the formal error and the number of jumps were significantly reduced in the re-processed solution. A discussion of new re-processing of the EPN network back to its beginning started among the workshop participants after that presentation. At least 6 LACs confirmed their plans to re-process the particular EPN sub-network and the analysis coordinator confirmed to take over the combination of the re-processed LAC solutions. It was agreed after some discussion to choose one person that overtakes the responsibility for the organizational and leading work of the re-processing. Christof Völksen declared to be prepared for this position. The next steps to push the EPN reprocessing will be taken by Christof Völksen. The EPN-CB will set up a data centre dedicated to the reprocessing; it will contain an on-line copy of all EPN data since the start of the EPN. A proposal for a reprocessing of the EPN shall be presented to the EUREF TWG in spring 2009.

Three presentations in session 5 ("Site, receiver, antenna and other issues") showed spectral analysis of EPN coordinate time series. Well-known annual and semi-annual but also diurnal and semi-diurnal signals have been identified by means of Fast-Fourier and Wavelet transformations. Valid absolute phase centre variations (APVCs) to be applied in EPN analysis have been discussed. Günter Stangl raised the question, whether actual APCVs which are in the official IGS ANTEX file, for particular Topcon antennae, should be used for EPN and especially the reprocessing. A lot of calibration values are transformed from relative to absolute values only and not calibrated at the robot. Stefan Schaer pointed out that consistency between IGS and EPN may be more important than correcting the APCVs. As the IGS re-processing is presently performed, the IGS cannot update its ANTEX files for antennae that are presently in use within the IGS. Before the next re-processing, however, the IGS will update its ANTEX files. It was concluded that for the moment the same APCV as the IGS would be used (with the exception of the individual calibrations). In the mean time the EPN CB will gather the necessary information concerning the missing APCV so that the ANTEX tables of the IGS can be updated as soon as allowed.
Elmar Brockmann proposed to publish at the EPN web site the ETRS89 coordinates of EPN stations officially adopted by the mapping agencies in the European countries. This is an important detail in the establishment of a European reference frame. The issue will be discussed within the TWG.

Jan Dousa presented a list of his ideas to stimulate discussion in working session 6 ("Wrap-up and closing session"). A couple of questions has been addressed and discussed:

• Improved Feedback to EPN LACs: Results of the LACs, e.g., differences/biases between the LACs, should be visualized at the EPN CB. Carine Bruyninx will come up with a first proposal for the selection of such items based on the weekly reports from the analysis coordinator.
• Visibility of the LAC: Several LACs have pointed out the need for visibility in order to allow them to continue to receive funding for their activities. In a first step, the EPN flyer will be updated with a reference to the contributing LACs. There was also a request to have a more official paper indicating that an agency is an EPN LAC.
• Re-Processing: This issue has already been discussed in session 4.
• EUREF ZTD combined product: The EPN ZTD combined product is important as a feedback for individual LACs performance and external validation of the utilized models. It should be compared to the other solutions of troposphere parameters, e.g., results from IGS, EUMETNET, radio-sondes or NRT combinations calculated by ASI. Jan Dousa, Rosa Pacione and Wolfgang Söhne will provide such comparison results and send them to the EPNCB for visualization.
• Rapid daily and NRT solutions: The rapid daily combined solution was identified to be a very important feedback to the station operators and the LACs within a short delay. COE, IGN and GOP announced to contribute with rapid daily solutions in the future and OLG and DEO are considering to follow. All EPN stations should thus be included in the rapid daily combination soon.
• In order to speed up the rapid product delivery, a fitted part of the ultra-rapid IGS orbits available at 3a.m. was proposed for the rapid solutions so the rapid combination could be finished before morning every day. The accuracy codes should be properly checked for possible problems with individual satellites from IGS ultra-rapid orbits.
• The potential of the hourlycombination for monitoring will be discussed between the LACs after the workshop.
• Real-time analysis: Wolfgang Söhne pointed out that we might expect first real-time analysis results from the IGS real-time pilot project distributed in real-time within the next year. An enhancement of EPN real-time data streams is also in preparation. EPN LACs were asked for their opinion about a contribution to any EPN real-time analysis activity. There are currently no plans of any LAC to get active in this field.
• Collaboration with EUMETNET and EGVAP: The collaboration with EUMETNET and EGVAP should be improved and extended in the future, especially if there are real-time or near real-time interests in EUREF in future. Elmar Brockmann explained that it is today possible to compare GNSS derived ZTD parameters with radio-sondes values due to the agreement on the data exchange between EUREF and EUMETNET.
• GNSS-GLONASS: The LACs are asked again to include all GLONASS observations of the EPN tracking stations in the analysis. Several LACs have pointed out their interest to start including GLONASS in their analysis.
• Analysis strategy: Changes of analysis options will be considered, when a new version of the Bernese Software has been released.

The Workshop was closed after the discussion.

Workshop Programme

Opening Session

J. Ihde: Welcome address from the Federal Agency for Cartography and Geodesy
H. Habrich: Welcome and workshop objective, setup of final schedule

Working Session 1: Reports from the EPN Coordination Group

Chair: Elmar Brockmann

C. Bruyninx, J. Legrand, F. Roosbeek: EPN Coordination Status and Plans
H. Habrich: Report on the EPN Analysis
W. Söhne: EUREF-IP - from Pilot Project to operational status
A. Kenyeres: Report on the EPN Time Series Analysis
W. Söhne: Status of the EPN troposphere product

Working Session 2: Local Analysis Centres reports

Chair: Carine Bruyninx

M. Valdes Perez de Vargas, J. Sanchez Sobrino: Current status of IGE LAC
E. Brockmann, D. Ineichen, S. Schaer: LPT Analysis Center Report
G. Stangl, C. Aichhorn, S. Krauss: OLG LAC 2006-2008 - EPN related activities
M. Figurski, T. Liwosz, K. Szafranek: Report of the WUT EPN Local Analysis Centre
B. Garayt: IGN LAC Report

Working Session 2: Local Analysis Centres reports (cont'd)

Chair: Günther Stangl

C. Völksen, W. Wende: Activities at the BEK LAC
J. Legrand, Q. Baire, N. Bergeot, C. Bruyninx, P. Defraigne, S. Pireaux, E. Pottiaux: Current activities and research at ROB LAC
C. Ferraro, R. Pacione, F. Vespe: ASI LAC Report
A. Kenyeres: SGO LAC report
L. Jivall, J. Johansson: Status report from NKG LAC

Working Session 3: Experiences with new processing strategies

Chair: Ambrus Kenyeres

R. Dach and the Bernese Software development team: Bernese Software recent developments and plans
S. Schaer: GNSS Tracking Issues

Working Session 4: New Analysis Products

Chair: Christof Völksen

A. Kenyeres, M. Figurski, J. Legrand: What can we expect from the EPN reprocessing ?
R. Pacione, F. Vespe, B. Pace, G. Colucci, D. Iacovone: ASI Near-Real Time products and related processing experiences
W. Söhne: Enhancement of EPN Real-Time Activities

Working Session 5: Site, receiver, antenna and other issues

Chair: Jan Hefty

J. Hefty, M. Igondova: Diurnal and semi-diurnal site coordinates variations resulting from processing with BV42 and BV50
K. Szafranek, M. Figurski, M. Galuszkiewicz: EPN reprocessed daily data analysis. Interpretation of disturbances caused by selected factors
P. Kaminski, M. Figurski: Time and frequency analysis of daily reprocessed solutions form selected EPN stations

Working Session 6: Wrap-up and closing session

Chair: Heinz Habrich

J. Dousa: LAC Questionnaire
All: Final Discussion