Flechtner F.M., Gruber Th., G?ntner A., Mandea M., Rothacher M., Sch?ne T., Wickert J. (Eds.) System Earth via Geodetic-Geophysical Space Techniques
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GGOS-D: Integration of Space Geodetic Techniques 535
7 The GGOS-D Terrestrial Reference Frame
A very accurate and stable terrestrial (and celestial) reference frame is one of the
most important contributions of a global geodetic observing system to GEOSS,
the Global Earth Observing System of Systems, as it provides the indispensable
metrological basis for all other Earth observing systems.
Based on the homogeneous and consistent time series of SINEX files generated
for the various techniques, a combined multi-year solution was produced for GGOS-
D. Refined combination methods were developed and applied for a simultaneous
adjustment of the terrestrial reference frame (station positions and velocities), Earth
orientation parameters and the celestial reference frame (quasar coordinates). The
quality of the resulting reference frames (TRF and CRF) together with the details of
the non-trivial combination process (local ties, extended parameter space, ...) may
be found in Angermann et al. (2009, chapter “GGOS-D Global Terrestrial Reference
Frame”, in this volume).
The reference frame results (TRF and CRF) also provided the basis for the sub-
sequent generation of consistent, high-quality time series of geodetic-geophysical
parameters describing the Earth System (see Sect. 8 and Nothnagel et al., 2009).
8 Comparisons and Validation of Long-Term Series of Geodetic
and Geophysical Parameters
The high-accuracy terrestrial and celestial reference frames generated in the frame-
work of the GGOS-D project (see Sect. 7) were the basis for the generation of very
homogeneous and consistent time series of the geodetic and geophysical parameters
that can be determined by the space geodetic techniques (site coordinates, geocen-
ter coordinates, EOPs, troposphere zenith delays and gradients, low-degree gravity
field coefficients). The time resolution of the different parameter types differ from
1to2h(ERPsandtroposphere zenith delays) to 1 week (SLR site coordinates,
low-degree gravity field coefficients). The contributions by Nothnagel et al. (2009)
and by König and König (2009, chapter “GGOS-D Integration with Low Earth
Orbiters”, in this volume) describe the comparisons and validation of these series
in more detail. Among others the following parameters and aspects were studied:
• Site coordinates: The site coordinates of GPS, VLBI and SLR were compared
in detail to validate the seasonal signals that are present in these time series,
i.e., to find out whether amplitudes and phases were the same for the different
space geodetic techniques, an indication that real geophysical phenomena and
not technique-specific artifacts are involved. A considerable part of the seasonal
signal in the GPS and VLBI time series seems to result from loading effects.
The effect of the thermal expansion of the radio telescopes on the VLBI site
coordinate time series was also studied and shows a systematic seasonal variation
in scale of about 0.3 ppb peak to peak.
536 M. Rothacher et al.
• Earth Orientation Parameters: x- and y-pole coordinates from a consistent com-
bination of GPS, VLBI and SLR showed an improvement compared to the
technique-specific solutions. For UT1-UTC a similar improvement could not
yet be achieved due to the systematic effects in the estimates of the s atellite
techniques.
Free Core Nutation (FCN) derived from VLBI and a combination of VLBI and
GPS was also analysed.
• Atmospheric Parameters: The troposphere zenith delays and gradients from
VLBI and GPS time series were compared and showed, in general, a very good
agreement. Systematic differences between the techniques may point at problems
in the corresponding local ties or in the GPS antenna phase center variations and
are, thus, an important diagnosis tool.
It should be mentioned that interesting contributions to this project also came
from the processing of the altimetry data, although this could not be fully docu-
mented in this volume because of limited space. The combination of the altimetry
results with those of the geometric space techniques and the gravity missions is not
trivial, because altimetry can only supply the ocean part of mass distribution and
transfer in the Earth system. All the other components have to be considered as well.
Only first steps in this direction could be made during the GGOS-D project, but con-
siderable progress has since been achieved in the Research Group “Earth Rotation
and Global Dynamic Processes” funded by the Deutsche Forschungsgemeinschaft
(DFG) (see, e.g., Göttl and Seitz, 2008).
9 Conclusions and Outlook
The realization of a high-precision terrestrial reference frame (TRF) and the gener-
ation of very homogeneous and consistent time series of geodetic and geophysical
parameters achieved in the framework of this project are very important steps for
various essential research topics such as sea level change, postglacial rebound, plate
tectonics and a possible increase of water vapor in the atmosphere. The accuracy
of the reference frames and time s eries available so far was limited by inconsisten-
cies in the modeling and parameterization and by reference frame changes. These
deficiencies have been overcome by the work done within the GGOS-D project.
The processing algorithms and strategies for the integration of the space geodetic
techniques that have been studied, developed and tested here can be seen as a proto-
type or a very reduced and small version of the data handling and processing part of
a global geodetic observing system. It is to be expected that the IAG services will
develop their products and services in a similar direction, establishing similar pro-
cedures and processing chains, but as an operational service also considering (near)
real-time aspects.
All time series and products generated during the GGOS-D project are archived
in the data management system of BKG. All these series are made available to the
GGOS-D: Integration of Space Geodetic Techniques 537
scientific community. We think that, because of their consistency and accuracy, these
time series are very valuable for further research, studies and comparisons. This is
also true for the multi-year solutions for the Terrestrial Reference Frame (TRF) and
the Celestial Reference Frame (CRF) that can be used by the IERS and the other
services for comparisons and combinations.
It is clear that the time series of SINEX files and geodetic and geophysical param-
eters have not yet been combined and exploited to the extent that would be possible.
Therefore, these time series will be the basis for further studies in the future such as
the full combination of the geometric (TRF, EOPs, CRF) and gravimetric parameters
(low-degree gravity field coefficients) that has not been fully achieved yet.
Acknowledgments This is publication no. GEOTECH-1287 of the programme
GEOTECHNOLOGIEN of the German Ministry of Education and Research (BMBF). The
work has been carried out to a large extent by the support of grants 03F0425A, 03F0425C,
03F0425D, and 03F0426A of BMBF.
References
Böhm J, Werl B, Schuh H (2006) Troposphere mapping functions for GPS and very long base-
line interferometry from European Centre for Medium-Range Weather Forecasts operational
analysis data. J. Geophys. Res. 111, B02406, doi: 10.1029/2005JB003629.
Fritsche M, Dietrich R, Knöfel C, Rülke A, Vey S, Rothacher M, Steigenberger P (2005) Impact
of higher-order ionospheric terms on GPS estimates. Geophys. Res. Lett. 32, L23311, doi:
10.1029/2005GL02432.
Göttl F, Seitz F (2008) Contribution of non-tidal oceanic mass variations to polar motion deter-
mined from space geodesy and ocean data. In: Sideris MG (ed.) Observing our Changing Earth,
IAG Symposia, vol. 133, Springer, pp. 439–445.
Skurikhina E (2001) On computation of antenna thermal deformation in vlbi data processing.
In: Behrend D, Rius A (eds) Proceedings of the 15th Working Meeting on European VLBI
for Geodesy and Astrometry, Institut d’Estudis Espacials de Catalunya, Consejo Superior de
Investigaciones Cientificas, Barcelona, pp. 124–130.
Steigenberger P, M, Dietrich R, Fritsche M, Rülke A, Vey S (2006) Reprocessing of a global GPS
network J. Geophys. Res. 111, B05402, doi: 10.1029/2005JB003747.
GGOS-D Data Management – From Data
to Knowledge
Wolfgang Schwegmann and Bernd Richter
1 Contributions for a Data and Information System
for GGOS-D
Inside the Joint Project the contributions for the development and implementation of
a data and information system for GGOS-D serve for the exchange of data and infor-
mation needed or provided by the project partners. Thus, the main task within the
first project phase was to build up a data and information infrastructure to coordinate
and facilitate the exchange of data as well as project related information between
the project partners. These administrative tasks, supporting the work of the project
partners in all work packages, are:
• Administration of a ftp server to store all data used within the joint project.
• Maintenance of a Web site to present information about the project to the public.
• Installation and administration of a project related Wiki
1
to report about and to
discuss the current work of the project partners on-line.
• Implementation of a GGOS-D email exploder to distribute information between
the project partners.
• Maintenance of a database to store information about meetings, talks and
publications of all co-workers within GGOS-D.
As the project is moving onwards the availability of high level tools to process
the data is of extreme importance. This includes general tools for the management
of metadata (creation, visualization and export), for search within the available data
with respect to technique, time, place, etc. and to generate time series of parame-
ters. More specific high level tools are necessary to investigate, analyze, combine
and visualize the data. Additionally, interfaces should be developed to provide
geodetic-geophysical time series, which will be used for the generation, analysis,
and validation of such time series.
B. Richter (B)
Bundesamt für Kartographie und Geodäsie, 60598 Frankfurt am Main, Germany
e-mail: bernd.richter@bkg.bund.de
1
http://en.wikipedia.org/wiki/Wiki
539
F. Flechtner et al. (eds.), System Earth via Geodetic-Geophysical Space Techniques,
Advanced Technologies in Earth Sciences, DOI 10.1007/978-3-642-10228-8_44,
C
Springer-Verlag Berlin Heidelberg 2010
540 W. Schwegmann and B. Richter
To implement these functionalities into a GGOS-D data and information system
three main tasks, respectively Work Packages (WP), have been identified:
1. WP 2100: Data Management for a Global Geodetic-Geophysical Observing
System.
2. WP 2200: Integration of External Geodetic-Geophysical Series.
3. WP 2300: Design of a Geodetic Metadata Catalogue Based on ISO Standards.
2 Data Management for a Global Geodetic-Geophysical
Observing System
The GGOS-D Data and Information System and its main components are shown in
Fig. 1. Thesystem is based on the IERS Data and Information System (Richter et al.,
2005) and its resources developed during the previous project phase (Richter and
Schwegmann, 2006). Thus, the basic functionality could be guaranteed already at
the beginning of the joint project. The IERS data management system is in charge of
collecting all IERS related products and data, it provides the functionality to assign
metadata to all data sets and incorporates tools for the selection of data sets (with
respect to technique, time, etc.) that make use of the stored metadata. The existing
system has been extended in order to collect and maintain the data within GGOS-D
and to assign metadata. Thus, the existing tools for the selection of specific data
Fig. 1 GGOS-D data and information system: overview
GGOS-D Data Management - From Data to Knowledge 541
sets can be used, too. This is important because with the growing duration of the
project it becomes necessary to select data files, produced by the techniques or by
combination and reaching back up to 20 years, in order to make special investi-
gations. For the SINEX files a strategy has been developed in close cooperation
with all project partners how the necessary metadata can be extracted automati-
cally from the files, because the huge amount of files makes a manual assignment
impossible. Additionally, a basic metadata editor has been developed in order to
allow the project partners to enter the metadata for individual files manually. The
user interfaces to search the archive as well as to edit and view metadata are shown
in Fig. 2.
Fig. 2 GGOS-D data and information system: user interfaces for search and metadata
management
542 W. Schwegmann and B. Richter
The most important objective of processing the weekly SINEX files is to derive
time series of geodetic-geophysical parameters. A data processing environment has
been developed to allow the user to create time series of all parameters contained
in the SINEX files and produce outputs in specific formats for further analyses.
Besides the “standard” time series (coordinates, EOP, geocentre) it will be possi-
ble to create special time series in the parameter space of the SINEX files, which
the users from the different fields of geosciences may optimize for their needs.
The goal is to create the demanded time series automatically in the background.
To ensure that the most up-to-date data sets are being used and to avoid multiple
sets of the s ame data, the time series are recreated as soon as new input data are
available.
Another important objective is to analyze the created time series with respect
to their quality and to compare the time series between each other. For this task
a generic data analysis tool is being developed at BKG within the project “Earth
Rotation Information System”. This project is part of the DFG sponsored Research
Unit “Earth Rotation and Global Dynamic Processes”.
2
Last but not least, another emphasis should lay in the visualization of the data
in order to create the basic data set by a combination of numerical input and visual
selection. Thus a generic plot tool has been developed to plot the generated time
series. Together with the data processing environment and the data analysis tool,
three high level tools are being developed. These tools allow an integrated process-
ing, analysis and visualization of all time series generated within the project as well
as to use external datasets for validation.
3 Integration of External Geodetic-Geophysical Series
To guarantee the reliability of the generated time series of geodetic-geophysical
parameters at the highest level, external geodetic-geophysical data series of the
IERS Global Geophysical Fluids Centre (GGFC)
3
(Chao et al., 2000) should
be integrated into the IERS Data and Information System for validation. For
this, a standardization of the GGFC data in cooperation with the eight Special
Bureaus of the GGFC is necessary, because the products are available in very het-
erogeneous formats. Unfortunately, the standardization efforts within the GGFC
Special Bureaus did not succeed. Thus the project partners decided to con-
centrate on the most important data sets of atmospheric angular momentum
(AAM) and oceanic angular momentum (OAM). These data sets have been
standardized and incorporated into the IERS Data and Information System and
can be further processed for the special validation tasks within the GGOS-D
project.
2
http://www.erdrotation.de
3
http://www.iers.org/MainDisp.csl?pid=75-53
GGOS-D Data Management - From Data to Knowledge 543
4 Design of a Geodetic Metadata Catalogue Based
on ISO Standards
International metadata catalogues allow to search for data structures in a broader
context. This makes it easier to find data sets from neighbouring fields of sci-
ence, and the available data sets may get a wider group of users. Therefore, the
metadata related to the data sets have been provided in a standardized form. The
ISO 19115 standard (ISO, 2003) to describe metadata of geographic data is widely
used by Meta Information Systems, e.g. by the German GeoPortal.Bund
4
hosted
by the BKG. In order to check the adaptability of the ISO 19115 standard for
Earth rotation and reference frames data, the metadata set used within the IERS
Data and Information System has been extended to be conform to this interna-
tional standard and the metadata of some IERS data sets have been included into
the GeoPortal.Bund. Even though the 19115 standard has been developed mainly
within the scope of geographic information data, it can also be applied to the data
sets within GGOS-D. In particular, the SINEX format has been extended by an ISO
19115 compliant metadata block. In the future, it should be investigated which inter-
national Meta Information Systems make use of the ISO 19115 standard in order to
propagate the available data sets within GGOS-D through them.
5 Summary
Within the Joint Project “Integration of Space Geodetic Techniques as the Basis for a
Global Geodetic-Geophysical Observing System (GGOS-D)” the contributions for
a data and information system for GGOS-D are of decisive importance and play a
central role to coordinate t he data and information flow between the project partners.
Besides the necessary infrastructure to facilitate the exchange of data and informa-
tion and to guarantee the availability of standardized data sets for all project partners,
high level tools to work with the data have been provided. Such tools comprise a data
processing environment to generate time series of geodetic-geophysical parameters
and to prepare data sets for the usage with other tools like the data analysis tool to
investigate the time series or the plot tool to visualize the data sets. Additionally,
the integration of external geodetic-geophysical data series from the IERS Global
Geophysical Fluid Centre (GGFC) is important for the external validation of the data
series. The most important data sets for this task have been examined and prepared.
Finally, a geodetic metadata catalogue based on ISO standards has been designed.
The goal is to incorporate the metadata, assigned to the data series with the help of
the data management system, into existing Meta Information Systems in order to
find applications beyond the group of geodetic users and to stimulate new scientific
investigations to derive knowledge from data. Thereby, the correct usage of the data
4
http://geoportal.bkg.bund.de
544 W. Schwegmann and B. Richter
series can be guaranteed by providing extensive metadata to describe the data and
scientific investigations are supported by providing high level tools to work with the
data.
Acknowledgments This is publication no.GEOTECH-1282 of the programme GEOTECH-
NOLOGIEN of BMBF and DGF, Grant 03F0426A.
References
Chao BF, Dehant V, Gross R et al. (2000) Space geodesy monitors mass transports in global
geophysical fluids. EOS Trans. Amer. Geophys. Union 81, 247–250.
ISO (2003) ISO 19115 Geographic Information Metadata, International Organization for
Standardization (ISO), Geneva.
Richter B, Schwegmann W (2006) IERS data and information system. In: Flury J, Rummel R,
Reigber C, Rothacher M, Boedeker G, Schreiber U (eds.), Observation of the Earth System
from Space, Springer, Berlin.
Richter B, Schwegmann W, Dick W (2005) Development of an information and database system
for the IERS: Status and outlook. J. Geodyn. 40, 487–493.
GGOS-D Consistent, High-Accuracy
Technique-Specific Solutions
Peter Steigenberger, Thomas Artz, Sarah Böckmann, Rainer Kelm,
Rolf König, Barbara Meisel, Horst Müller, Axel Nothnagel,
Sergei Rudenko, Volker Tesmer, and Daniela Thaller
1 Introduction
One of the main characteristics of the GGOS-D project is the generation of homo-
geneous time series of geodetic and geophysical parameters for the individual
space-geodetic techniques and their combination. In order to achieve the high-
est accuracy possible for the geodetic and geophysical parameters, three topics
are indispensable: First, all individual solution series must be generated using the
most up-to-date analysis strategy as well as the best models available. Second, if
parameters or models are common to more than one space-technique, the same
parameterization and the same models must be applied for all techniques. And
finally, the whole time series must be generated using the pre-defined analysis
strategy.
Contributions of three space-geodetic techniques are considered within
GGOS-D, namely GPS, SLR and VLBI. We have no single software package avail-
able that is capable to generate solution series of the highest-possible quality for
all these techniques. However, there are specialists for each technique amongst the
institutions cooperating within GGOS-D, so that we have two software packages for
each of the space-techniques. All software packages use the classical least squares
adjustment technique with the Gauss-Markov model. They are adopted to use pre-
defined common standards so that the homogeneity of the individual contributions
can be guaranteed. The availability of two contributions per technique allows to
investigate the level of homogeneity achieved, and to quantify the level of the anal-
ysis noise that is left. To be able to reliably detect signals in the time series of
geodetic and geophysical parameters, it is clear that the time series must be as long
as possible. Therefore, all data available that allow a reasonable determination of
the parameters of interest are processed within GGOS-D.
P. Steigenberger (B)
Institute of Astronomical and Physical Geodesy, Technische Universität München,
D-80333 München, Germany
e-mail: steigenberger@bv.tum.de
545
F. Flechtner et al. (eds.), System Earth via Geodetic-Geophysical Space Techniques,
Advanced Technologies in Earth Sciences, DOI 10.1007/978-3-642-10228-8_45,
C
Springer-Verlag Berlin Heidelberg 2010