NATIONAL REPORT OF THE FEDERAL REPUBLIC OF ... - IAG Office

18 Commission 1 – Reference Frames
The contribution of the IVS for ITRF2005 has been computed
by the IVS Analysis Coordinator's office at the Institute
of Geodesy and Geoinformation of the University of Bonn
(e.g. VENNEBUSCH et al., 2006). For this purpose the IVS
Analysis Centers, two of them being the Leipzig Branch
of BKG and DGFI, provided datum-free normal equation
matrices in Solution INdependent EXchange (SINEX)
format for each 24-hour observing session to be combined
on a session-by-session basis. The German contributions
to the ILRS include the computation of SLR time series
solutions by the ILRS Analysis Centres at DGFI and GFZ
and their combination performed by the ILRS Backup
Combination Centre at DGFI (e.g. KELM, 2003, MÜLLER
et al., 2005). The German contributions to the IGS include
the processing of GPS time series solutions by the IGS
Analysis Centres at GFZ and ESOC, Darmstadt.
Besides the official IGS solutions submitted for the
ITRF2005 computation, a complete reprocessing from the
raw GPS observations has been started by the FESG of the
Technical University Munich and the Institute for Planetary
Geodesy (IPG) of the Technical University Dresden (e.g.
STEIGENBERGER et al., 2006). In 2006, also the IGS has
decided to perform such a homogenous reprocessing and
recombination of the GPS data, which then will serve as
input for future ITRF realizations.
DGFI and IGN computed each one solution for ITRF2005
using the times series solutions (or normal equations). The
common processing of time-dependent station positions and
EOP shall ensure the consistency of the terrestrial reference
frame and the orientation of the Earth in space. Both ITRS
Combination Centres used their own software and applied
their preferred methodology. A description of the combination
methodology applied at DGFI is published in ANGER-
MANN et al. (2007). Comparisons between the IGN and
DGFI solutions show a good agreement after similarity
transformations, but a significant difference in the SLR
scale was found due to the different computation strategy.
It has been agreed by IGN and DGFI to perform further test
computations to assess the effect of the differences in the
combination strategies.
Various studies related to the terrestrial reference computations
were performed, which include the weighting of the
different space geodetic observations (e.g. KELM, 2003),
the local tie implementation within the inter-technique
combination (e.g. KRÜGEL and ANGERMANN, 2007) and
the effect of time-variable effects in station positions on
the terrestrial reference frame results (e.g. MEISEL et al.,
2007). FESG and GFZ Potsdam performed investigations
on the impact of the combination of GPS and Galileo as
well as of GPS and Low Earth Orbiters (LEO) on the global
reference frame (e.g. ROTHACHER and SVEHLA, 2003;
KÖNIG et al., 2005; ZHU et al., 2003). In a cooperation
between the Geodetic Institute of the University Hannover
and DGFI a new stochastic approach was developed for the
intra-technique combination, assuming that the variance
of the input data sets of different Analysis Centres have a
common part resulting from the variance of the observations
(observation noise) and an individual part coming
from the individual analysis strategy (analysis noise). First
results of this new stochastic approach are presented in
KUTTERER et al. (2007).
Reference Frame for Europe (EUREF)
The EUREF Sub-Commission was constituted at the IUGG
General Assembly held in Vancouver, 1987, under the
umbrella of Commission X – Global and Regional Geodetic
Networks of Section 1 – Positioning. As a result of the new
IAG structure at the IUGG General Assembly held in
Sapporo, 2003, EUREF was integrated within Sub-Commission
1.3 “Regional Reference Frames” (e.g. TORRES et
al., 2005).
The objective of EUREF is the definition, realization and
maintenance of the European Reference Systems, in close
cooperation with the IAG components and Euro-
Geographics, the consortium of the National Mapping and
Cadastre Agencies (NMCA) in Europe. The Terms of
Reference (ToR), which were adopted at the annual symposium
held in Bratislava (June 2004), contain the description
of EUREF, its objectives, activities, organisation and the
rules for membership according to the general rules expressed
in the Statutes and By-laws of IUGG and IAG (see
http://www.euref-iag.net/html/ Overview_of_EUREF_
Terms_of_reference.html).
The forum, where activities are discussed and decisions are
taken is the annual symposium, organized since the EUREF
foundation in 1987. Current activites are governed by the
Technical Working Group (TWG). The results of EUREF
are available in the symposia proceedings as well as on the
EUREF homepage (http://www.euref_iag.org/).
Since the beginning, Germany is intensively engaged in
EUREF. The secretariat of EUREF is incorporated at the
German Geodetic Commission in Munich. Several German
geodesists are members of the TWG. The organization of
numerous EUREF campaigns was organized and mostly
subsidized by BKG in Frankfurt a.M. and Leipzig. Numerous
colleagues from other countries were guests of BKG
to be trained in the analysis of GPS networks. The proceedings
of the EUREF symposia were compiled by the EUREF
President and Secretary, the printing was financed by BKG.
German institutions also contribute significantly to the
EUREF Permanent Network (EPN). The EPN is a network
of continuously operating GNSS stations, primarily
installed for reference frame maintenance. Since 2003, more
than 30 new EPN stations were installed, bringing the total
number of stations to almost 200, from which 16 stations
are operated by German institutions. The current status of
the EPN is visible at the EPN Central Bureau web site at
http://www.epncb.oma.be. In order to optimise the data
processing within the EPN, the principle of distributed
processing is used. In this approach the EUREF Permanent
Network is divided in sub-networks, which are separately
processed by different EPN Local Analysis Centres
(LAC's). They submit weekly free-network solutions
(SINEX format) to the EPN Regional Data Centre at BKG.
There are two LAC’s operated by German institutions: The
Bavarian Committee for International Geodesy in Munich
(BEK: “Bayerische Kommission für die Internationale