International Gravimetric Bureau (Bureau Gravimétrique International, BGI)

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1 International Gravimetric Bureau 1 International Gravimetric Bureau (Bureau Gravimétrique International, BGI) Director: Sylvain Bonvalot (France) Structure The BGI is the scientific service of IAG aimed at ensuring the data inventory and the long term availability of the gravity measurements acquired at the Earth surface. Its main task is the collection, validation and archiving of all kind of gravity measurements (relative or absolute) acquired from land, marine or airborne surveys and the diffusion of the derived data and products to a large variety of users for scientific purposes. The BGI activities are coordinated with those of other IAG gravity services (ISG, IGETS, ICGEM, IDEMS) through the International Gravity Field Service (IGFS). The BGI has its central bureau in Toulouse (France) and operates with the support of various institutions from France (CNES, CNRS/INSU, IGN, IRD, SHOM, BRGM, IFREMER, Universities of Toulouse, Paris, Strasbourg, Montpellier and Le Mans) and from Germany (BKG). Its directing board includes representative of the supporting institutions and a representative of IAG and of IGFS. For more information on the BGI structure and membership, see the following references: - The International Gravimetric Bureau. In: The Geodesist s Handbook, 2016, H. Drewes, Eds. (International Association of Geodesy). Journal of Geodesy, Journal of Geodesy DOI: /s z - BGI website : Overview During the reporting period, the BGI has continued to support scientific and other users of gravity data. The BGI mainains the 4 global reference databases for relative gravity measurements (from land and marine surveys), for absolute gravity measurements and for reference gravity stations. BGI continues its activity of compilation, validation, archiving and distribution of the surface measurements of the Earth s gravity field. It also realize and distributes derived products (global or regional grids of gravity anomaly) and gravity processing or analysis software s. During the period, also has carried out regional gravity data compilation and validation for international projects related with geoid or gravity anomaly computations (GEOMED-2, ALP-Array, etc.) and has participated as co-chair of the IAG Joint Working Group for the realization of the Global Absolute Gravity Data Reference System. Finally, BGI is also involved in the evaluation of innovative instrumentations for static and dynamic measurements of the Earth gravity such as absolute gravity meters based on cold-atoms technologies. Activities 1. Global gravity databases and products Most of the databases and services provided by BGI are available from the BGI website ( It gives access to the four global database of gravity observations: 1) Relative measurements from land surveys; 2) Relative measurements from marine surveys; 3) Reference gravity stations related to the former IGSN71 and Potsdam 1930 networks, 4) Absolute measurements.

2 Report of the IAG Vol. 40 Travaux de l AIG Relative gravity database The most frequent service BGI can provide is the consultation and retrieval of gravity data and information over local or regional areas. Data requests are made through the BGI website at the following links. Few millions of relative data are currently distributed each year to scientific users. For larger areas (regional to global), BGI also propose grids of gravity anomalies (free air, Bouguer, isostatic). - land database: - marine database: Absolute gravity database The global database for absolute gravity measurements is jointly operated by BGI and BKG (Bundesamt für Kartographie und Geodäsie, Germany). This relational database (AGrav) is capable of storing information about stations, instruments, observations and involved institutions. By this, it allows the exchange of meta-data and the provision of contact details of the responsible institutions as well as the storage and long term availability of gravity data and processing details. The database can be accessed from two mirrored sites at BGI and BKG. - absolute database: ; A simple exchange format (project files) which includes all relevant information and is known by the majority of users, was selected. In this way the upload of data to the database is possible by any contributor, using a web based upload form. The provided information ranges from meta-data (localization of stations) up to full information on the absolute determination of the gravity field on a given site (raw or processed data, description of measurement sites, etc.). The collection and archiving of absolute gravity data has been continued in Figure 1: WEB interface of the Absolute Gravity database (BGI-BKG) Current status (06/2017) : 1147 stations / 4031 observations / 73 instruments / 63 institutions An improved version of the database has been also initiated (development in progress) in order to support the project of realization of the international absolute gravity reference system (IAG/IGFS/GGOS initiative) and to provide a better link between observations provided by both absolute and superconducting gravity meters. This new version (see presentations at EGU2017 and IAG/IASPEI 2017) keeps a similar structure but will provide new functionalities as for instance: interactive maps, plot of time series, link to superconducting gravity times series, etc.

3 International Gravimetric Bureau 3 Figure 2: On-going development of the new AGrav version (Wziontek et al., EGU 2017) 1.3. Regional or global gravity anomaly grids The BGI provided new access or links to high resolution global or regional grids of gravity anomaly such as those derived from the World Gravity Map (Bonvalot et al., CGMW World Gravity Map, 2012 ; Balmino et al., Journal of Geodesy, 2012) ; EGM2008 (Pavlis et al., JGR 2012) or GGMPlus (Hirt et al., GRL, 2013). Figure 3: Examples of grid extraction from the global WGM2012 gravity model ( 2. Contribution to regional gravity projects During the reporting period, BGI has contributed to the GEOMED2 project which aims at computing an updated estimate of the geoid in the Mediterranean area. It has specially performed gravity data compilation and validation using marine gravity measurements collected over the entire Mediterranean basin. The GEOMED2 is currently in progress and should be finalized in Details on this work are given in: Barzaghi et al., (2017a, 2017b, 2016, 2015), Lequentrec-Lalancette et al. (2016) and Bruinsma et al.(2017).

4 Report of the IAG Vol. 40 Travaux de l AIG Fig. 4: Free air gravity anomalies over Mediterranean Sea from marine data analysed at BGI for the GEOMED2. (see Lequentrec-Lalancette et al., IAG Symposia Series. 2016). 3. Contribution to the definition of the International Absolute Gravity Reference System We chair the IAG JWG Establishment of the International Absolute Gravity Reference System (Chair: H. Wziontek, Co-Chair: S. Bonvalot). This IAGRS aims at fulfilling the following objectives: (1) The need for accurate and long term stable reference provided by a primary network of reference stations where gravity is monitored with absolute gravimeters. Such primary network is already a central part of the IAG resolution 2 (2015) and should also contribute to the infrastructure of GGOS Core sites. (2) The need for secondary network of gravity stations which ensures accessibility of the system by a global set of sites, compatible with the above defined reference level, to any user. The aim of this secondary network is to identify and make accessible the largest number of absolute gravity values observed worldwide from field surveys of laboratory measurements to provide absolute reference to any purpose (relative gravity surveys, calibration lines, etc.). This secondary network must be considered as well in order to establish a replacement for IGSN 71. The main objectives of this future network has been described in Wilmes et al. (2016) and presented at a dedicated splinter meeting during EGU Contributions to absolute gravimetry BGI teams are also involved in the evaluation of innovative instrumentations for measuring the Earth gravity field (such as cold-atoms gravity meters). For instance, we are contributing to the evaluation of the new Absolute Quantum Gravity (AQG) meter recently developed by MUQUANS ( This evaluation includes characterization of performances and accuracy, sensibility analysis and comparisons with reference gravity meters such as the FG5 and A10 Micro-g LaCoste instruments or other cold-atoms gravity meters (Bonvalot et al., 2016a, 2016b; Pereira and Bonvalot, 2016). BGI also continued the development of software or utility tools dedicated to gravity data validation and processing. In this context, an application (MGL_QuickView) dedicated to provide a fast synthetic plot of absolute gravity measurements taken with FG5 and A10 meters is made available for users (

5 International Gravimetric Bureau 5 Fig 5a: Absolute Quantum Gravity (AQG) meter recently developed by MUQUANS ( Scientific events International meetings (as scientific committee) Fig 5b: MGL_QuickView utility tool: Quick view of Micro-g LaCoste FG5 / A10 absolute gravity measurements (Gabalda and Bonvalot, 2016) 09/2016 : GGHS - Joint IAG / IGFS Meeting. Thessaloniki, Greece 04/2016 : 4 th IAG Symposium on Terrestrial Gravimetry. St. Petersburg, Russia International meetings 08/2017 : IAG/IASPEI Joint Assembly 2017 ; Kobe, Japan 04/2017 : EGU General Assembly 2017 ; Vienna, Austria 12/2016 : AGU General Assembly 2016 ; San Francisco, USA, 09/2016 : GGHS - Joint IAG / IGFS Meeting, Thessaloniki, Greece 05/2016 : ESA Living Planet Symposium ; Pragua, CSR, 04/2016 : EGU General Assembly 2016 ; Vienna, Austria, 04/2015 : EGU General Assembly 2015 ; Vienna, Austria International project workshops and splinter meetings 03/2017 : Workshop on Absolute Gravity Reference System ; EGU, Vienna, Austria 03/2017 : Workshop on ALP-Array project ; EGU, Vienna, Austria 03/2017 : Workshop on IGETS/BGI databases ; EGU, Vienna, Austria 03/2017 : 3 rd GEOMED-II Workshop ; Roma, Italy 09/2016 : CNES-NASA Workshop «Atom Interferometry / Space Geodesy» ; Paris, FR 02/2015 : 2 nd GEOMED-II Workshop ; Thessaloniki, Greece IAG structure & working groups IAG JWG : Establishment of a Global Absolute Gravity Reference System (AGRS) (Chair: H. Wziontek, Co-Chair: S. Bonvalot) Advisory Board of IGFS - Consortium member of GGOS - IAG Sub-commissions : «Gravimetry, Gravity networks», «Absolute Gravimetry»

6 Report of the IAG Vol. 40 Travaux de l AIG Publications / Communications Selected publications Assessment of GOCE Geopotential Models. Newton's Bulletin, Issue n 5, June BGI-ISG (Eds). Balmino, G. et S. Bonvalot (2016). Gravity anomalies. In: E.W. Grafarend (ed.), Encyclopedia of Geodesy, Springer International Publishing Switzerland DOI: / _45-1. Bonvalot, S. (2016). The International Gravimetric Bureau. In The Geodesist s Handbook 2016, H. Drewes (ed). (International Association of Geodesy). Journal of Geodesy DOI: /s z Lequentrec-Lalancette, MF.; Salaün, C.; Bonvalot, S.; Rouxel, D.; Bruinsma, S. (2016). Exploitation of marine gravity measurements in the validation of global gravity field models. IAG Symposia Series. IUGG General Assembly in Prague, Springer International Publishing Switzerland DOI: /1345_2016_258 Pallero, J.L.G., Fernandez-Martınez, J.L., Bonvalot, S., Fudym, O. (2015). Gravity inversion and uncertainty assessment of basement relief via Particle Swarm Optimization. Journal of Applied Geophysics. DOI: /j.jappgeo Pallero, J.L.G., Fernandez-Martınez, J.L., Bonvalot, S., Fudym, O. (2017). 3D gravity inversion and uncertainty assessment of basement relief via Particle Swarm Optimization. Journal of Applied Geophysics. Volume 139, April 2017, Pages Peirera, F. et S. Bonvalot (2016). Cold atom absolute gravimetry. In: E.W. Grafarend (ed.), Encyclopedia of Geodesy, Springer International Publishing Switzerland DOI / _30-1. Wilmes, H., L. Vitushkin, V. Palinkas, R. Falk, H. Wziontek, S. Bonvalot (2016). Definition and Realization of a Global Absolute Gravity Reference System. IAG Symposia Series. IUGG General Assembly in Prague, Springer International Publishing Switzerland DOI: /1345_2016_245 Selected communications 2017 Barzaghi R., Vergos G., Albertella A., Carrion D., Tziavos I., Grigoriadis V., Natsiopoulos D., Bruinsma S., Bonvalot S., Seoane L., Reinquin F., Lequentrec-Lalancette M-F., Salaun C., Bonnefond P., Knudsen P., Andersen O., Simav M., Yildiz H., Basic T., Varga M., Bjelotomic O. (2017). The GEOMED2 project: Geoid estimation in the Mediterranean Area. IAG/IASPEI Joint Assembly 2017; July 30-August 4, 2017, Kobe, Japan (G ). Barzaghi R., Vergos G., Albertella A., Carrion D., Tziavos I., Grigoriadis V., Natsiopoulos D., Bruinsma S., Bonvalot S., Seoane L., Reinquin F., Lequentrec-Lalancette M-F., Salaun C., Bonnefond P., Knudsen P., Andersen O., Simav M., Yildiz H., Basic T., Varga M., Bjelotomic O. (2017). The GEOMED2 project: Geoid and circulation in the Mediterranean Area. IAG/IASPEI Joint Assembly July 30-August 4, Kobe, Japan (G02-P-18). Bruinsma S., Bonvalot S., Reinquin F., Seoane L. (2017). GEOMED2 gravimetric versus combined geoid model. IAG/IASPEI Joint Assembly July 30-August 4, Kobe, Japan (G ). Vergos G., Grigoriadis V., Barzaghi R., Carrion D., Bonvalot S., Barthelmes F., Reguzzoni M., Wziontek H., Kelly K. (2017). IGFS geoportal development for gravity, geoid, GGM and DEM data. IAG/IASPEI Joint Assembly 2017, July 30-August 4, 2017, Kobe, Japan (G07-P-04). Wziontek H., Falk R., Bonvalot S., Ruelke A. (2017). New design and facilities for the International Database for Absolute Gravity Measurements (AGrav): A support for the Establishment of a new Global Absolute Gravity Reference System. IAG/IASPEI Joint Assembly 2017, July 30-August 4, 2017, Kobe, Japan (G07-P-03) Bonvalot S., Le Moigne N., Gabalda G., Merlet, S., Desruelle, B., Lautier-Gaud, J., Menoret, V., Vermeulen, P. (2016). The new Absolute Quantum Gravimeter (AQG): first results and perspectives. International Symposium on Gravity, Geoid and Height Systems September 19-23, Thessaloniki, Greece Bonvalot S., Le Moigne, N. Merlet, S., Desruelle, B., Lautier-Gaud, J., Menoret, V., Vermeulen, P. (2016). The new Absolute Quantum Gravimeter (AQG): first results and perspectives. Geophysical Research Abstracts Vol. 18, 2016EGUGA B Barzaghi, R., G. Vergos, A. Albertella, D. Carrion, N. Cazzaniga, I. Tziavos, V. Grigoriadis, D. Natsiopoulos, S. Bruinsma, S. Bonvalot, L. Seoane, F. Reinquin, MF Lequentrec-Lalancette, C. Salaun, P. Bonnefond, P. Knudsen, O. Andersen, M. Simav, H. Yildiz, T. Bašić, M. Varga, O. Bjelotomić, AJ Gil (2016). Theoretical and numerical investigations towards a new geoid model for the Mediterranean Sea The GEOMED2 project. Geophysical Research Abstracts Vol. 18, EGU , 2016

7 International Gravimetric Bureau 7 Barzaghi, R., Vergos, G.S., Albertella, A., Carrion, D., Cazzaniga, N., Tziavos, I.N., Grigoriadis, V., Natsiopoulos, D., Bruinsma, S., Bonvalot, S. and Seoane, L. (2016). Improved representations of the Mediterranean Geoid within the GEOMED 2 project. Contributions of local gravity, GOCE and Cryosat2 data. In ESA LP 2016, Conference: ESA Living Planet Symposium Lauria, E., M.C. Pacino, D. Blitzkow, D. Piñon, S. Miranda, S. Bonvalot, G. Gabalda, C. Tocho (2015). RAGA - AAGN (Argentine Absolute Gravity Network). IUGG General Assembly, July 2015, Praga, CSR Desruelle, B., Le Moigne, N., Bonvalot, S., Menoret. V., Vermeulen, P., Merlet, S. (2015). Quantitative analysis of a transportable matter-wave gravimeter. AGU Fall Meeting. December 14-18, 2015, San Francisco, USA. Blitzkow, D., AC. Oliveira Cancoro de Matos, G. do Nascimento Guimarães, MC Pacino, E. Lauría, R. Forsberg, S. Bonvalot, G. Gabalda, F. Flores, A. Echalar, H. Parra, J. Neira, N. Guevara, R. Alvarez, JN. Hernandez, CA. Castro Junior, MC Lobianco, M. Nunes (2015). Gravity surveys and quasi-geoid model in South America - extra efforts. IUGG General Assembly, July Praga, CSR Barzaghi, R., A.Albertella, N. E.Cazzaniga, S. Bonvalot, S. Bruinsma, M.F. Lequentrec, I.N. Tziavos, G.S. Vergos, V.N. Grigoriadis (2015). The GEOMED 2 project: A high resolution geoid of the Mediterranean Sea Note for BGI users & contributors / Attribution of DOI The contribution to the BGI databases of worldwide scientists, agencies or institutions involved in relative or absolute gravity data acquisition is crucial for improving the global knowledge of the Earth gravity field and providing the best service to the IAG/GGOS community. It is reminded that any dataset or metadata derived from land, marine or airborne surveys or from compilation works (point data or grids) can be deposited as public or proprietary information. This enables BGI to ensure a long term archiving of the data and to validate the incoming gravity observations in a global reference frame and restore them (public data only) in standard and unified formats useful for various users. In order to better reference and acknowledge these contributions, a DOI (Digital Object Identifier) will be attributed to any gravity dataset or product deposited at BGI. This new service will ensure a proper reference to authors and institutions who have acquired or compiled gravity data and a better traceability of improvements provided by these local or regional surveys to the global gravity data coverage. Users are also invited to make reference to the following DOI for acknowledging BGI services or data. Recommended citation: Bureau Gravimetrique International (BGI). DOI: /BGI Contacts for updating BGI databases or obtaining DOI for data, products or software: bgi@cnes.fr ; agrav@bkg.bund.de