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24 Introduction The contributions of German scientists were focussed to the development of concepts for the definition and realization of vertical reference systems as well as to implementation activities in the global, European and national frame. The work was organized in interdisciplinary working groups, mainly the Inter-commission Project 1.2 Vertical Reference Frames, a common Project of Commission 1 and Commission 2, the Sub-commission for Reference Frames in Europe EUREF, and the Working Committee of the Surveying Authorities of the German States (AdV). The combination of different geodetic techniques is an integrated part of all concepts for height determination and the realization of vertical reference frames. Especially the satellite gravity missions CHAMP, GRACE and in the next step GOCE in connection with local geoid densifications and GNSS measurements will lead to an essential progress for the unification of the different height reference frames. Global Vertical Reference System (GVRS) In 2003 IAG has founded the Inter-commission Project 1.2 Vertical Reference Frames to study the consistent modelling of both, geometric and gravimetric parameters and to provide the fundamentals for the installation of a unified global vertical reference frame. The main tasks were: – Elaboration of a proposal for the definition and realization of a global vertical reference system; – Study of combination procedures for height data sets from different techniques; – Study of information on regional vertical systems and their relations to a global vertical reference system for practical applications; – Unification of regional (continental) height systems; – Harmonization of globally used height data sets. The results of the work of the ICP1.2 are documented in Conventions for the Definition and Realization of a Conventional Vertical Reference System (CVRS, CVRF). In the CVRS/CVRF conventions a general concept for the definition and realization of a unique, global vertical reference system is worked out. The CVRS conventions are aligned to the IERS 2003 Conventions. Parts of the IERS 2003 conventions are the basis for the CVRS conventions. Vertical Reference Frames J. IHDE 1 A global unified vertical reference system as International Vertical Reference System (IVRS) can be realized by: – A global network of stations coordinated in ITRF with co-location between permanent GNSS, tide gauges, in some stations gravity permanent (SG) and periodically (AG) – A conventional global gravity model (CGGM) from satellite gravity missions only – Both based on a set of conventionally numerical standards. Regional and national height reference systems can be integrated in an IVRS by GNSS/levelling aligned to ITRF and using the CGGM and the numerical standards. Proposed items for continuation: – Discussion of the results of ICP1.2 (GGAS action) – Initiation of a pilot project for an IVRS realization on the basis of the TIGA-PP, GGP and IGFS for AG and a CGGM (call for participation as IGFS action) – Decision about numerical standards as task of GGOS in cooperation with IAU. The project continuation shall realize in cooperation with other organizations, especially the International Association of Hydrological Sciences (IAHS), the International Association for the Physical Sciences of the Oceans (IAPSO), the International Hydrographic Organisation (IHO), the International Federation of Surveyors (FIG), and the Interservice Geospatial Working Group (IGeoWG) of NATO. German scientists basically contributed to this working group by: – Definition and realization of a global vertical datum: the zero height level. Since the different physical height types (orthometric and normal heights) refer to different reference surfaces (namely, geoid and quasigeoid), the studies are focused in appointing a unified reference surface, which serves as a zero level to both types of heights and allows the different countries to keep the physical heights they prefer, but in a unified vertical reference system. – Determination of a conventional geopotential value (W0). Although the W0 value of a vertical datum can arbitrarily be selected, it is preferred to introduce a quantity, which agrees with the state of the art of the present observing techniques of the Earth’s gravity field. In this way, W0 was determined by applying different approaches (mean value of the geopotential values at the sea surface, solution of the fixed gravimetric geodetic 1 Johannes Ihde: Bundesamt für Kartographie und Geodäsie, Richard-Strauss-Allee 11, D-60598 Frankfurt am Main, Germany, Tel. +49 - 69 - 6333 206, Fax +49 - 69 - 6333 425, e-mail johannes.ihde@bkg.bund.de
oundary value problem, etc.), different mean sea surface models (CLS01, KMS04, GFSC00.1, and a series of annual models from 1993 to 2001 derived at DGFI from T/P), and different global gravity models (EGM96, TEG4, GGM02S, EIGEN-CG03C, EIGEN-GL04S). – Unification of the existing vertical datums. This topic is concentrated on the formulation of a combined system of observation equations based on spirit levelling, GNSS positioning, and geoid determination. It includes the common analysis of tide gauge registrations, satellite altimetry data analysis and GNSS positioning at those tide gauges which serve as vertical datums in the classical height systems. This analysis is carried out in the frame of the IGS TIGA project. A meeting of the Working Group "Theoretical Geodesy" took place to the topic "Fundamental questions of vertical datum and a world height system" in the Institute of Theoretical Geodesy of the University of Bonn on September 12th, 2006. Science colleagues from Germany and the Netherlands as well as representatives of the national survey from a few federal states took part in the meeting. In the course of the informal meeting a number of lectures was given followed by dedicated discussions. It turned out that the issue of the choice of a suitable vertical datum and of the connection of regional datum systems, but also the question of a practicable solution that is closely connected to this arouse intense discussions again and again. European Vertical Reference System (EVRS) The main activities to realize the European Vertical Reference System (EVRS) are carried out in the frame of the IAG Sub-commission EUREF. In the last four years EUREF initiated several height projects: The European Combined Geodetic Network (ECGN), the densification of European Vertical Reference Network (EUVN-DA) and the readjustment of the United European Levelling Network (UELN). The combination of the UELN and ECGN activities will lead to an EVRS 2007 solution. The Federal Office for Cartography and Geodesy (BKG) is the responsible EVRS data and analysis centre. All European levelling data of EUREF are stored and analysed at BKG including the information systems to present the results via internet. The European activities were related in two directions: i. Selection and validation of related height information ii. Preparation of a new EVRS solution to store all height related geo-information data of the European Commission in a homogeneous vertical system. The updating and maintenance of the UELN databank was continued by the data of the national Bulgarian First Order Levelling Network, the data of the current Danish First Order Levelling Network, the data of the 5th precision levelling of the Netherlands, the data of the newly measured 1st order levelling networks of Finland, Norway and Sweden. In this context the ’Land Uplift Model’, used by NGK for the readjustment of Scandinavia, was transferred. J. Ihde: Vertical Reference Frames 25 The measuring data by means of this model were reduced to the epoch 2000. Germany participated in the activities carried out for the EUVN_DA project within the scope of the provision of the levelling heights of the stations in the EVRF2000 system. The project serves to derive a new European geoid. To be able to ensure that in the case of an interim change of the net datum and the integration of new data into the UELN, respectively, the heights of all EUVN_DA stations do refer uniformly to the relevant current epoch, the geopotential differences between the EUVN_DA stations and the neighbouring UELN nodal points were adopted into the database, thus they will enter into any future UELN adjustment. Re-measurement of the German First Order Levelling Network (DHHN) Since 2003 the conceptual preparation of a re-measurement of the German First Order Levelling Network (DHHN) was performed in the frame of the Working Group "Renewal of the DHHN92" of the AdV. On the basis of an analysis of the current state of height networks in Germany the Working Group discussed urgent questions of effort for and accomplishment of a renewal of the levelling network. Objectives of a re-measurement of the levelling network are the examination of the official height system DHHN92 for detection of stresses and height changes (diagnosis), the optional introduction of a new official height status, the integration of the height reference system into a future integrated spatial reference system and the creation of bases for scientific investigations (e.g. determination of recent crustal movements). Correspondingly, the concept comprises besides digital geometrical precision levelling from the state surveying agencies during the years 2006 – 2011 an additionally epoch equal GNSS campaign integrating 250 selected points of the levelling network and nearly 300 reference stations of different GNSS networks (IGS, EPN, GREF, SAPOS) in 2008. In addition, BKG will carry out absolute gravity measurements on 100 of the field stations as from 2008. As economically reasonable variant that is realizable within a period of about 5 years, at first a partial renewal of the existing network with a levelling length of about 14.000 km (about 50 % of the existing network) was intended. By now, additional efforts of the surveying agencies let expect re-levelling of approximately 75% of the first order network. The network configuration follows the run of existing 1st order levelling lines. For linking the network to the neighbouring states and the connection of coast gauges, attention was paid to the inclusion of levelling lines along the state boundaries and the coasts of North and Baltic Sea. In addition, the selected lines should have as little height difference changes as possible between the previous two levelling epochs. To check the compliance with these conditions the horizontal gradients of vertical height difference changes were determined and analysed from the observations of the last two levelling epochs that are stored in the DHHN databank.
Page 1: DEUTSCHE GEODÄTISCHE KOMMISSION be
Page 4 and 5: Adresse des Herausgebers / Address
Page 7 and 8: Contents Commission 1 - Reference F
Page 9: COMMISSION 1 REFERENCE FRAMES 7
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Page 16 and 17: 14 Introduction Celestial Reference
Page 30 and 31: 28 Satellite altimetry provides a p
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Page 52 and 53: 50 Introduction In the reporting pe
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Page 60 and 61: 58 1. Modelling Techniques Fundamen
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Page 72 and 73: 70 Introduction The four years sinc
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74 Commission 2 - Gravity Field SCH
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Introduction The determination of E
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Introduction German investigations
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In Europe, there are detailed inves
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SASGEN, I., MULVANEY R., KLEMANN V.
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enabling us to map the behaviour of
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NAUJOKS M, JAHR T., JENTZSCH G.,. K
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nental hydrosphere. Thus, interpret
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M. Thomas, M. Soffel, H. Drewes: Ea
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M. Thomas, M. Soffel, H. Drewes: Ea
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observed that the resulting masscha
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Since 2001, the IERS Central Bureau
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COMMISSION 4 POSITIONING AND APPLIC
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The main highlights in the past fou
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VLBI Space Geodetic Techniques (VLB
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A. Nothnagel: Space Geodetic Techni
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A. Nothnagel: Space Geodetic Techni
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also be able to track the broadband
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CHEN X., DEKING A., LANDAU H., STOL
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SEEBER G.: Beitrag für „Directio
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2003, WÜBBENA et al. 2006a) or in
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Permanent GNSS Networks, including
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G. Weber, M. Becker, J. Ihde: Perma
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G. Weber, M. Becker, J. Ihde: Perma
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General remarks The continuous and
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Introduction GNSS Based Sounding of
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J. Wickert, N. Jakowski: GNSS Based
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J. Wickert, N. Jakowski: GNSS Based
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References ADAM N.: TerraFirma Qual
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Introduction The period 2003 - 2007
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procedures and surveying instrument
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Motivation During the last years, n
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AVILA-RODRIGUEZ J.-A., PANY T., EIS
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SEIFERT A., KLEUSBERG A. (2003): An
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IAG PROJECTS 143
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The Global Geodetic Observing Syste
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KRÜGEL M., TESMER V., ANGERMANN D.
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Inter-commission Committees (ICC) A
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After the restructuring of the IAG
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Introduction Physical Aspects of Ge
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H. Drewes, M. Soffel: Physical Aspe
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W. Keller, W. Freeden: Mathematical
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W. Keller, W. Freeden: Mathematical
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H. Kutterer, W.-D. Schuh: Quality M
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B. ICC on Planetary Geodesy (ICCPG)
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Introduction Various space missions
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Photogrammetrie, Fernerkundung und
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