| Since 2011 | Co-Chair, Program Committee of the GEOS Science and Technology Stakeholder Network Workshop, Bonn, Germany, August 2012. |
| Since 2011 | Co-chair, Program Committee for the Fifth IGCP 565 Project Workshop on "Improving regional water management in Africa and Asia on the basis of geodetic water cycle monitoring", October 2012, Capetown, South Africa. |
| Since 2011 | Co-chair, Program Committee for the Fourth IGCP 565 Project Workshop on "Integration of geodetic observations and products in models of the hydrological cycle - Support for water management through hydrological models and data assimilation", November 22-23, 2011, Johannesburg, South Africa. |
| Since 2011 | Co-Chair, European Science Foundation Workshop "Understanding Extreme Geohazards: The Science of the Disaster Risk Management Cycle", November 28-December 1, 2011, Sant Feliu de Guixous, Spain. |
| Since 2010 | Co-Chair, Program Committee of the Workshop "Building a User-Driven GEOSS: Methods to Capture, Analyze, and Prioritize User Needs, April 10, 2011, Sydney, Australia. |
| Since 2010 | Member, GEO Task Force on Gap Analysis. |
| Since 2010 | Co-Chair, Program Committee of the Workshop "Connecting GEOSS and its Stakeholders in Science and Technology", Bonn, Germany, May 9-11, 2011. |
| Since 2010 | Member, Program Committee for the Workshop "Earth Observation Support for Sustainable Tourism in Small Island States", March, 9-11, 2011, San Juan, Puerto Rico. |
| 2010-2011 | Co-chair, Program Committee for the third IGCP 565 Project Workshop on "Separating Hydrological and Tectonic Signals in Geodetic Observations", October 11-13, 2010, Reno, Nevada, USA. |
| 2010 | Member, Organizing Committee for the US-Africa Workshop on "Expanding the AfricaArray Network to Support Multidisciplinary Science in Africa", June 2-4, 2010, Washington, D.C., USA. |
| 2010 | Member, Program Committee for the Workshop "Decision-Making Support For Coastal Zone Management, Water Resources & Climate Change In Africa", February, 15-18, 2010, Cotonou, Benin. |
| 2010 | Co-chair of the Program Committee for the Workshop "Building a Geohazards Community of Practice in Support of GEO Work Plan Tasks and GEOSS Implementation," January 18-22, 2010, Paris, France. |
| 2010-2011 | IEEE Representative to the GEO Science and Technology Committee |
| 2010-2011 | IEEE Representative to the GEO User Interface Committee |
| Since 2010 | Co-Chair, GEOSS Stakeholder Network. |
| 2009 | Co-Convener of four sessions, AGU Fall Meeting, December 2008, San Francisco ("Severe Storms and Sea level Rise: A Challenge for Science and Society," "Extreme Natural Hazards: Risk Assessments, Forecasting, and Decision Support," "The Global Geodetic Observing System: Scientific Requirements and Applications," "Science and Technology in GEO and GEOSS"). |
| 2009 | Co-chair of the Program Committee, Second Annual Workshop of the IGCP 565 Project "Towards a Roadmap for Future Satellite Gravity Missions", September 30 - October 2, 2009, Graz, Austria |
| 2009 | Co-Convener, "Earth observation and the Global Geodetic Observing System (GGOS)", Session at the IAG Symposium "The Global Geodetic Observing System: Science and Applications", August 31-September 4, 2009, Buenos Aires, Argentina. |
| 2009 | Co-Convener, "The Global Geodetic Observing System: Ground and Space-based Infrastructure for Earth Science", Session G8, EGU General Assembly, April 2009, Vienna, Austria |
| Since 2009 | Co-Chair, Geohazards Community of Practice of the Group on Earth Observations (GEO). |
| 2009 - 2011 | Point of Contact and Task Lead for the GEO Task ST-09-02 "Promoting Awareness and Benefits of GEO in the Science and Technology Community" |
| 2008 | Co-Convener, "Global Geodetic Observing System: Science and Instrumentation", Sessions G31C and G33A, AGU Fall Meeting, December 2008, San Francisco. |
| Since 2008 | Member of the GGOS ad hoc Working Group on an ITRS ISO Standard |
| 2008 | Chair of the Program Committee, First Annual Workshop of the IGCP 565 Project "Science of geodetic monitoring of the hydrological cycle", December 2008, San Francisco, USA |
| 2008 | Co-Convener, "Earth observation and the Global Geodetic Observing System (GGOS)", Session at the IAG Symposium "Gravity, Geoid and Earth Observation GGEO 2008", June 23-27, 2008, Chania, Crete, Greece. |
| 2008 | Co-Chair of the Program Committee of the first GEO Workshop of the Coastal Zone Community of Practice: "GEOSS Support for Decision-Making in the Coastal Zone: Managing and Mitigating the Impacts of Human Activities and Natural Hazards in the Coastal Zone", June 2008, Athens, Greece |
| Since 2008 | Co-Chair of the GEO Coastal Zone Community of Practice (CZCP) |
| 2008 | Panel member, "Climate Change and Transportation Panel", Water Canada, May 14, 2008.
|
| 2008 | Co-Convener, "GGOS: Observing and Interpreting Earth's Mass Transports", Session G12, EGU General Assembly, April 2008, Vienna, Austria |
| 2008 | Member of the Science Advisory Group for the Delta Commission of the Dutch Parliament on future sea level changes |
| Since 2008 | Lead Project Leader of the IGCP 565 Project "Developing the Global Geodetic Observing System into a Monitoring System for the Global Water Cycle" |
| 2007-2010 | GGOS Representative to the GEO Science and Technology Committee |
| 2007 | Organization of the GEO/GGOS Workshop 2007, November 2007, Frascati, Italy |
| Since 2007 | Member of IAG's Inter-Commission Working Group 2 "Concepts and terminology related to Geodetic Reference Systems" |
| 2007-2010 | Chair of the GGOS Working Group on GEO Relations |
| 2007 | IAG/GGOS Representative in the GEO Task Force 2 for the preparation of the Ministerial Summit on Earth Observation |
| Since 2007 | Member of the GEO "Coastal Zone" Community of Practice |
| 2006 | Organization of the GGOS Workshop 2006, October 2006, Munich, Germany |
| 2006-2010 | GGOS Representative to the GEO Architecture and Data Committee |
| Since 2007 | Point of Contact and Task Lead for the GEO Task DA-09-02c (former AR-07-03) "Global Geodetic Reference Frames" |
| 2006-2009 | Coordinator and Lead Editor of the GGOS 2020 Strategy Process: "The Global Geodetic Observing System: Meeting the Requirements of a Global Society on a Changing Planet in 2020" |
| 2005-2008 | GGOS Representative to the Joint GARS and IGOS-P Steering Committee for the Geohazards Theme |
| 2005-2010 | GGOS Representative to the GEO User Interface Committee |
| 2005-2010 | Vice-chair of the Steering Committee of the Global Geodetic Observing System (GGOS) and member of the Executive Committee |
| 2005-2007 | IAG delegate to the GEO Working Group on Tsunami activities |
| 03/2005 - 01/2006 | Principle Investigator, "Appraisal of relative sea level rise scenarios for Venice" |
| 12/2004 - 08/2005 | Principle Investigator, "National geodetic infrastructure - current status and future requirements" |
| 2004-2009 | Member of the IAG Delegation to the annual GEO Plenary and Ministerial Summits on Earth Observations, Deputy head of delegation |
| Since 2004 | Member of the Advicory Committee for the IERS Conventions |
| 2004-2006 | External Expert member of the Project Team, European Sea Level Service Research Infrastructure (ESEAS-RI) |
| 2004-2005 | IAG delegate to the GEO Working Group "User requirements" |
| 2004-2006 | Chair of the GGOS working group "Copyrights, Data Access Policy, Publishing, and Certification" |
| Since 2002 | Associate Member of the International Earth Rotation Service |
| 12/2002 - 06/2004 | Principle investigator, "Determination of geodetic coordinates of the EGNOS RIMS and NLES sites" |
| 12/2002 - 06/2004 | Coordinator, Norwegian Research Project OCTAS "Ocean Circulation and Transport between North Atlantic and Arctic Sea" |
| 11/2002 - 06/2004 | Coordinator, EU-Project "ESEAS-Research Infrastructure" |
| 06/2002 - 06/2004 | Principle investigator, Galileo System Test Bed V1 Stand-alone Test Case
"Geodetic Galileo" |
| Since 2002 | Co-chair, Special Bureau for Loading of the Global Geophysical Fluid Center of the IERS, since 2004 chair |
| 2001 - 2004 | Director, Central Bureau of the European Sea Level Service (ESEAS) |
| 2000 - 2004 | National Delegate, IAG Commission V and XIV. |
| Since 2000 | Associated Member of the International VLBI Service |
| 2000 | Organisation of the IGS Network Workshop and the COST 716 Workshop "Towards operational GPS-Meteorology" in Oslo, Norwegen |
| 2000-2006 | Secretary of the EGS subsection II.B2: "Global and Regional Interdisciplinary Networks" |
| 1999 - 2004 | National Delegate & Co-chair (since 2001), COST Action 716: "Exploitation of ground-based GPS for climate and numerical weather prediction applications" |
| Since 1998 | Associated member of the International GPS Service |
| 1998 | Organisation of the WEGENER 98 meeting in Norway |
| 1998 - 2002 | Chair of the COST Action 40 "European Sea Level Observing System (EOSS)", including the organization of biannual meetings and two international workshops. |
| 1997 - 2004 | Member of the Ny-Alesund Science Manager Committee (NySMAC) |
| 1997 - 2002 | Responsible Scientist in the EU TMR Project "VLBI-Europe" and the EU-funded Large Scale Facility Ny-Alesund |
| Since 1996 | Editor-in-Chief (for Geodesy) of Physics and Chemistry of the Earth |
| 1996 - 2000 | Secretary of the EGS subsection II.5: "Geodetic aspects of global change phenomena" |
| Since 1994 | Member of the Editorial Board of the Journal of Geodynamics |
| Since 1992 | Several times convener at annual meetings of the EGS/EGU, the German Geophysical Society, AGU, as well as IUGG assemblies |
| 1995 - 1999 | Chairperson of the Science Panel of the WEGENER Board |
| 1995 - 1999 | Contractor of the EU project SELF II |
| 1993 - 1994 | Subcontractor of the EU project SELF |
| 1989 - 1999 | Member of the WEGENER-Consortium and participation in the DOSE-Programme of NASA |
| 1989 - 1997 | Participation in the German national Earth rotation research programme |
| 1988 - 1995 | Participation in the LAGEOS-II-Programme of NASA and ASI |