NKG Working Group for Geodynamics Copenhagen, 23 –24 April, Tasks of a new Working Group on Absolute Gravimetry Herbert Wilmes Federal Agency for Cartography and Geodesy, Frankfurt (BKG) NKG Working Group for Geodynamics Copenhagen, Denmark, 23 – 24 April 2008

NKG Working Group for Geodynamics Copenhagen, 23 –24 April, Motivation Requests for reliable and time-dependent gravity data with global coverage (Satellite gravity field missions, GGOS, Mass transports in the system Earth, etc.) At present, no agreed standards for AG observations, processing, results Instrument accuracy much better than the the valid gravity reference system Present working group on AG comparisons (BIPM, regional comparisons) can not cover additional tasks

NKG Working Group for Geodynamics Copenhagen, 23 –24 April, Parameter space for combination of gravity and geometry X... position, W... Earth gravity potential, T... disturbance potential, H... phys. height,... Variation of the geom. geom. height (After Rottacher and Ihde)

NKG Working Group for Geodynamics Copenhagen, 23 –24 April, Gravimetric residual functions after combining AG and SG Stations: Bad Homburg (D), Wettzell (D), Medicina (It)

NKG Working Group for Geodynamics Copenhagen, 23 –24 April, Motivation (cont.) Combination of terrestrial observations with satellite gravity field missions CHAMP, GRACE, GOCE Detection of periodic mass changes water storage difference simulated with the global hydrological model WGHM hydrological mass signal Global continental pattern of differences between monthly GRACE gravity field solutions Ref.: Ilk et al.: Mass transport and mass distribution in the Earth system

NKG Working Group for Geodynamics Copenhagen, 23 –24 April, Combination of SG and AG in Concepcion (Chile) Example for strong gravity variations at a geodetic reference station

NKG Working Group for Geodynamics Copenhagen, 23 –24 April, Structure of AG-related working groups BIPM IAG IGFS International Gravity Field Service R. Forsberg Working Group on Absolute Gravimetry H. Wilmes Comm. 2 Gravity Field Y. Fukuda Subcomm. 2.1 Gravimetry and Gravity Networks L. Vituskin CCM-W.G. on Gravimetry IAG-SG 2.1 Comparison of AG L. Vitushkin

NKG Working Group for Geodynamics Copenhagen, 23 –24 April, IGFS structure and relation to GGOS IGFS BGI CNES Toulouse IGeS Polimi Milano ICET U. F. Polynesia ICGEM GFZ Potsdam Technical Centre NGA St. Louis Advisory Board Affiliate scientists IDEMS DeMontfort UK IGFS is a unified "umbrella" IAG service, which will - Coordinate collection, validation, archiving and dissemination of gravity field related data - Coordinate exchange of software of relevance for gravity field activities - Coordinate courses, information materials and general public outreach relating to the earth's gravity field GGOS has e.g. identified a unified global absolute gravity network as a major element missing in the long-term basic GGOS network. A special purpose of the IGFS will be to coordinate the gravity field services in relation to GGOS – the Global Geodetic Observing System – and take initiatives to cover missing elements, e.g. the provision of “combination” solutions” of gravity field related quantities, analogous to e.g. the IERS.

NKG Working Group for Geodynamics Copenhagen, 23 –24 April, Role of the new working group: a) Standards and Conventions Define standards for gravity data observation procedures Define data reduction (tides, atmosphere, …), Define data exchange format and archive Define the standards for associated data (pressure, hydrology…) Define data processing methods (adjustment,…) Define gravity anomaly/disturbance computation (free-air, Bouguer, …) Define the gravity reference system (replace IGSN71) Define the geopotential reference system (W 0, GRS80) Evaluate and recommend relevant geophysical models Requests from GGOS to the IGFS

NKG Working Group for Geodynamics Copenhagen, 23 –24 April, b) Networks and Communications Design and realization of the global absolute gravity network Design and realization of the global superconducting gravity network Contribute to the definition and realization of the global height system Contribute to the GGOS co-located site network (AG, SG, W,…) Provide gravity field parameters at tide gauge stations Integrate gravity and leveling networks Contact with external networks (oceanic, atmospheric, hydrologic,…) Making gravity data, gravity models and products available via IGFS Services and Central Bureau (web site)

NKG Working Group for Geodynamics Copenhagen, 23 –24 April, Objectives and Tasks of the Working Group The proposed Working Group on Absolute Gravimetry will have following objectives and tasks: 1.Design and promote a worldwide AG network with repeated observations 2.Define standards for observation and processing of absolute gravity data 3.Set up a database for global AG observations 4.Support the combination of repeated AG measurements and SG time series 5.Enable the combination of gravity and geometric observations 6.Prepare an improved gravity reference system 7.Data policy for use of AG observations Participants of the NGOS community are very welcome to contribute and actively support the aims of the working group! Comments? Propositions? Ideas? Special areas of interest? Which is most important?