Journal of large-scale research facilities, 2, A83 (2016) http://dx.doi.org/10.17815/jlsrf-2-136 Published: 09.08.2016 Geomagnetic Observatories GFZ German Research Centre for Geosciences * Instrument Scientists: - Jürgen Matzka, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany, phone: +49 (0)33841 624-18, email: jmat@gfz-potsdam.de Abstract: In this article we brie�y describe the geomagnetic observatories operated or supported by the Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences (GFZ), their scienti�c and societal use in the light of a global approach, their main data products and their dissemination process, as well as their instrumentation. The geomagnetic observatories of GFZ are part of the ’Modular Earth Science Infrastructure’ (MESI). 1 Introduction The geomagnetic �eld is generated by electric currents in the Earth’s core, ionosphere and magneto- sphere as well as induced electric currents in the Earth’s mantle and oceans. An additional contribution originates from the magnetisation of the lithosphere. Geomagnetic observatories are a versatile tool to study these currents and the associated processes in Earth and its surrounding space environment. In contrast to variation magnetometers or absolute scalar magnetometers, observatories provide cali- brated vector data in an absolute reference frame (Matzka et al., 2010). Long-term, homogenous time series allow the study of secular variation of the core �eld and of trends in space climate. Geomag- netic observatories and geomagnetic measurements from satellites (e.g. ESA’s Swarm mission, Olsen et al. (2013)) complement each other due to their di�erent space/time constellation, e.g. for the char- acterisation of geomagnetic variations with local time. Observatories are in particular important for studying long-term trends and induction phenomena. GFZ globally operates geomagnetic observato- ries and plays an active role in supporting geomagnetic observatories worldwide through cooperation agreements (see Figure 1 for a full overview on geomagnetic observatories with GFZ cooperation). A focus area for GFZ geomagnetic observatories is the South Atlantic Anomaly, i.e. the area from South America to South Africa that is characterised by low, and decreasing, geomagnetic �eld strength. *Cite article as: GFZ German Research Centre for Geosciences. (2016). Geomagnetic Observatories. Journal of large-scale research facilities, 2, A83. http://dx.doi.org/10.17815/jlsrf-2-136 1 http://jlsrf.org/ http://dx.doi.org/10.17815/jlsrf-2-136 http://dx.doi.org/10.17815/jlsrf-2-136 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A83 (2016) http://dx.doi.org/10.17815/jlsrf-2-136 2 Data products and their dissemination Data are typically given in local Cartesian coordinates in a topocentric geodetic coordinate system (ge- ographic North X, geographic East Y and vertical down Z) in units of nT, and time is given in UTC. The data is provided in three di�erent types, representing a progressively improved calibration and quality control: provisional (near real-time), quasi-de�nitive (with about 1 to 2 months delay) and de�nitive (typically 3 to 18 months delay). De�nitive yearly, hourly and minute mean values are distributed through the World Data Centre for Geomagnetism (Edinburgh), UK, (abbreviation: WDC, http://www.wdc.bgs.ac.uk/) and through INTER- MAGNET (www.intermagnet.org, e.g. (St-Louis, B. and INTERMAGNET, 2012). INTERMAGNET is a consortium that sets and controls international standards for geomagnetic observatories and organises a peer review of the de�nitive data prior to publication. Preliminary mean values are available from INTERMAGNET in near real time (up to a few days delay), quasi-de�nitive minute mean values are typically available on a monthly basis (Matzka, 2013; Peltier & Chulliat, 2010). The International Association of Geomagnetism and Aeronomy (IAGA), INTERMAGNET and the WDC for Geomagnetism are closely cooperating with users, data providers and also with each other. The free and open access to geomagnetic observational data for scienti�c purpose has a long tradition in the geo- magnetic community. Commercial data use, e.g. in support of navigating horizontally-drilled oil wells, typically leads to commercial agreements with the customers, e.g. oils service companies. Some of the geomagnetic data from observatories operated or supported by GFZ that currently do not ful�l INTERMAGNET standards is available through SuperMAG (Gjerloev, 2012), which is one of sev- eral projects to provide such data from a single website (http://supermag.uib.no/). Data are routinely redistributed, e.g. from INTERMAGNET to the WDC for Geomagnetism as well as to SuperMAG. Acknowledgement is given directly to GFZ or indirectly to INTERMAGNET. Download statistics are available from INTERMAGNET. 3 Global approach GFZ operates the geomagnetic observatories Niemegk (established in 1930) and Wingst (established in 1938) in Germany as well as one each in the British Overseas Territories St Helena (Korte et al., 2009) and Tristan da Cunha (Matzka et al., 2011, 2009). An observatory on the Azores is in the process of being set up. GFZ currently has cooperation agreements with various partners (for a full list see the acknowledgements) regarding the operation of geomagnetic observatories in Antarctica, Bolivia, Brazil, Bulgaria, India, Indonesia, Namibia, Portugal, Romania, Russia, and Ukraine. There are various levels of involvement by GFZ ranging from providing instrumentation to observatory planning, set up, maintenance, training, sharing of operating costs, data calibration and quality control, depending on the cooperation. Niemegk serves as a central observatory and on its premises there are test, calibration and archive facilities as well as workshops and computer infrastructure maintained by sta� specialized on observatory operations to run or support all observatories in our network. The observatory network allows GFZ and its partner institutions to close gaps in global coverage or to con- centrate on monitoring and exploring regional phenomena of special scienti�c interest, like the South Atlantic Anomaly, or speci�c high, low and mid-latitude current systems in Earth’s space environment. Fig. 1 shows a map of the geomagnetic observatories operated or supported by GFZ, including those that are in the process of being established. 2 http://dx.doi.org/10.17815/jlsrf-2-136 https://creativecommons.org/licenses/by/4.0/ http://dx.doi.org/10.17815/jlsrf-2-136 Journal of large-scale research facilities, 2, A83 (2016) Figure 1: Geomagnetic observatories operated and supported by GFZ (red dots) of which, at the time of writing, 13 are INTERMAGNET observatories. The black dots are other INTERMAGNET observatories (see text). 4 Instrumentation Typically, three instruments are operated in an observatory. These measure (i) the absolute �eld strength, (ii) the absolute direction of the geomagnetic �eld vector, and (iii) variations of certain vector components. In the following, we list what can be considered as standard instruments for geomag- netic observatories and these are typically used at GFZ’s geomagnetic observatories. Absolute �eld strength is usually measured by GSM-19 or GSM-90 proton or Overhauser magnetometers manufac- tured by Gem Systems, Canada. Absolute �eld direction is measured with a �uxgate probe mounted on a non-magnetic theodolite of type Theo 010 or Theo 020 previously manufactured by Zeiss Jena, Germany. Variations are measured by suspended 3-compent �uxgate vector magnetometers of type FGE manufactured by Technical University of Denmark. The variations are logged with 1 Hz or faster. The absolute measurements are performed manually on a weekly basis and are used to calibrate the variation measurements to yield the absolute data stream. An absolute accuracy of 1 nT can ideally be achieved. Acknowledgements GFZ’s sta� members Oliver Bronkalla, Heinz-Peter Brunke, Jürgen Haselo�, Achim Morschhauser, Carsten Müller-Brettschneider, Hannelore Podewski, Stefan Rettig, Manfred Schüler and Katrin Tornow at Niemegk geomagnetic observatory are acknowledged. The cooperat- ing institutes Universidad Mayor De San Anders (Bolivia), National Institute of Geophysics, Geodesy and Geography (Bulgaria), South African National Space Agency (SANSA, South Africa), Institute of Cosmophysical Research and Aronomy (IKFIA, Russia), Institute of Cosmophysical Research and Radio Wave Propagation (IKIR, Russia), Indian Institute of Geophysics (IIG, India), National Geophysical Re- search Institute (NGRI, India), Geological Institute of Romania (IGR, Romania), Observatório Nacional (ON, Brasil), Institute of Geophysics (IGF, Ukraine), Mataram University (Indonesia), Technical Uni- versity of Denmark (DTU, Denmark), Alfred-Wegener-Institute (Germany) are acknowledged. Kirsten Elger is acknowledged for valuable comments that greatly improved the manuscript. 3 http://dx.doi.org/10.17815/jlsrf-2-136 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A83 (2016) http://dx.doi.org/10.17815/jlsrf-2-136 References Gjerloev, J. W. (2012). The supermag data processing technique. Journal of Geophysical Research: Space Physics, 117(A9). http://dx.doi.org/10.1029/2012JA017683 Korte, M., Mandea, M., Linthe, H.-J., Hemshorn, A., Kotzé, P., & Ricaldi, E. (2009). New geo- magnetic �eld observations in the South Atlantic Anomaly region. Annals of Geophysics, 52(1). http://dx.doi.org/10.4401/ag-4631 Matzka, J. (2013). Preparation of quasi-de�nitive (QD) data for the observatories Narsarsuaq, Qeqertar- suaq and Tristan da Cunha. In P. Hejda, A. Chulliat, & M. Catalan (Eds.), Real instituto y observatorio de la armada en san fernando (pp. 50–53). Matzka, J., Chulliat, A., Mandea, M., Finlay, C. C., & Qamili, E. (2010). Geomagnetic observations for main �eld studies. Space Science Reviews, 155(1), 29–64. http://dx.doi.org/10.1007/s11214-010-9693-4 Matzka, J., Husøy, B. A. W. D. P. L. W. S. C., B.-O., Repetto, R., Genin, L., Merenyi, L., & Green, J. J. (2011). The geomagnetic observatory on tristan da cunha: Setup, operation and experiences. Data Science Journal, 10, IAGA151–IAGA158. http://dx.doi.org/10.2481/dsj.IAGA-22 Matzka, J., Olsen, N., Maule, C. F., Pedersen, L. W., Berarducci, A. M., & Macmillan, S. (2009). Ge- omagnetic observations on Tristan da Cunha, South Atlantic Ocean. Annals of Geophysics, 52(1). http://dx.doi.org/10.4401/ag-4633 Olsen, N., Friis-Christensen, E., Floberghagen, R., Alken, P., Beggan, C. D., Chulliat, A., . . . Visser, P. N. (2013). The Swarm Satellite Constellation Application and Research Facility (SCARF) and Swarm data products. Earth, Planets and Space, 65(11), 1189–1200. http://dx.doi.org/10.5047/eps.2013.07.001 Peltier, A., & Chulliat, A. (2010). On the feasibility of promptly producing quasi-de�nitive magnetic observatory data. Earth, Planets and Space, 62(2), e5–e8. http://dx.doi.org/10.5047/eps.2010.02.002 St-Louis, B. and INTERMAGNET (Ed.). (2012). Technical Reference Manual Version 4.6, INTERMAGNET. Retrieved from http://www.intermagnet.org/publication-software/technicalsoft-eng.php (accessed on 10 March 2016) 4 http://dx.doi.org/10.17815/jlsrf-2-136 http://dx.doi.org/10.1029/2012JA017683 http://dx.doi.org/10.4401/ag-4631 http://dx.doi.org/10.1007/s11214-010-9693-4 http://dx.doi.org/10.2481/dsj.IAGA-22 http://dx.doi.org/10.4401/ag-4633 http://dx.doi.org/10.5047/eps.2013.07.001 http://dx.doi.org/10.5047/eps.2010.02.002 http://www.intermagnet.org/publication-software/technicalsoft-eng.php https://creativecommons.org/licenses/by/4.0/ Introduction Data products and their dissemination Global approach Instrumentation