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Logo: Sonderforschungsbereich geo-Q
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Logo: Sonderforschungsbereich geo-Q
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C04 - Regional gravity field modeling & relativistic geodesy

Einstein’s general relativity theory predicts that two ideal clocks will in general run at different rates with respect to a common (coordinate) timescale if they move with a relative velocity or are under the influence of different gravitational fields, which is associated with the relativistic redshift effect. For the usual case of two earthbound clocks at rest, the corresponding clock frequency shift or relativistic redshift effect is directly proportional to the gravity (gravitational plus centrifugal) potential difference at both sites, where one part in 1018 clock frequency shift corresponds to about 0.1 m2s-2 in terms of the gravity potential difference, which is equivalent to 0.01 m in height. Hence, geodetic knowledge of heights and the Earth’s gravity potential can be used to predict frequency shifts between local and remote (optical) clocks, and vice versa, frequency standards can be used to determine gravity potential differences. The latter technique has variously been termed “chronometric levelling”, “relativistic geodesy”, and “chronometric geodesy”. It offers the great advantage of being independent of any other geodetic data and infrastructure, with the perspective to overcome some of the limitations inherent in the classical geodetic approaches. For example, it could be used to interconnect tide gauges on different coasts without direct geodetic connections and help to unify various national height networks, even in remote areas.

This project connects the areas of time metrology with optical clocks and classical physical geodesy. In the first instance, the classical geodetic and the chronometric levelling results are used for a mutual validation, which is important to build confidence in the new generation optical clocks and the associated uncertainty budgets as well as in view of future geodetic applications of the optical clocks, while later on all results shall be combined to obtain optimal geopotential estimates. In this context, geodetic knowledge on the gravity potential is first derived from the geometric levelling technique (together with gravity observations) and secondly from GNSS (Global Navigation Satellite System) positions and the results from gravity field modelling (e.g., disturbing potential, (quasi)geoid, based on the geodetic boundary value problem (GBVP) theory), the latter procedure being also denoted as the GNSS/GBVP or GNSS/geoid approach; both techniques have their own particular strengths and limitations, with the geometric levelling approach giving superior accuracies over shorter distances (few km), while the GNSS/GBVP approach should be beneficial over longer distances (1000 km and more).

Project C04 aims at providing the relativistic redshift corrections and the corresponding gravity potential values with best possible accuracy. For this purpose, GNSS and levelling observations have been performed at the relevant clock sites, and emphasis is put on the development of an improved high-resolution (quasi)geoid model for Central Europe, targeting in the long term an accuracy of 1 cm or better. This includes a revised mathematical modelling regarding the observation equations, the consideration of the atmosphere and the topography, the use of a high-degree reference geopotential model, the combination, data weighting and error estimation procedure, as well as a closed-loop simulation and software test.

The pictures below show GNSS, levelling and gravimetric measurements at and around the Max-Planck-Institut für Quantenoptik (MPQ), Garching, one of the planned clock sites within geo-Q.

GNSS, levelling and gravimetric measurements

Scientists working on this project

Lin Miao
email: linmiaoife.uni-hannover.de

phone: +49 511 762-5176
details

Dr.-Ing. Ludger Timmen
email: timmenife.uni-hannover.de

phone: +49 511 762 3398
details

Selected Publications


Peer-Reviewed Literature

Voigt C., Denker H. and Timmen L.  (2016): Time-variable gravity potential components for optical clock comparisons and the definition of international time scales, Metrologia, Volume 53, Number 6 more
DOI: 10.1088/0026-1394/53/6/1365


Non Peer-Reviewed Literature

Denker H. (2015): A new European gravimetric (quasi)geoid EGG2015, XXVI General Assembly of the International Union of Geodesy and Geophysics (IUGG), Earth and Environmental Sciences for Future Generations, Prague, Czech Republic, 22 June – 02 July 2015, Abstract G02p-424

Denker H., Timmen L. and Voigt C. (2015): Gravity field modelling for optical clock comparisons, XXVI General Assembly of the International Union of Geodesy and Geophysics (IUGG), Earth and Environmental Sciences for Future Generations, Prague, Czech Republic, 22 June – 02 July 2015, Abstract G02p-431

Voigt C., Denker H. and Timmen L. (2015): Investigation of time-variable components of the gravity potential for optical clock comparisons, XXVI General Assembly of the International Union of Geodesy and Geophysics (IUGG), Earth and Environmental Sciences for Future Generations, Prague, Czech Republic, 22 June – 02 July 2015, Abstract G02p-423
DOI: 10.1088/0026-1394/53/6/1365


Presentations, Talks and Posters

Grosche G., Lisdat C., Quintin N., Shi C., Raupach S. M. F., Grebing C., Nicolodi D., Stefani F., Al-Masoudi A., Dörscher S., Häfner S., Robyr J.-L., Chiodo N., Bilicki S., Bookjans E., Koczwara A., Koke S., Kuhl A., Wiotte F., Meynadier F., Camisard E., Abgrall M., Lours M., Legero T., Schnatz H. Sterr U. Denker H., Charonnet C., Le Coq Y. Santarelli G., Amy-Klein A., Le Targat R., Lodewyck J., Lopez O. and Pottie P.-E. (2017): 1400 km optical fiber link tests whether French and German clocks tick alike, Precise Time and Time Interval Meeting, Monterey, California, USA, 30 January – 2 February, 2017

Grotti J., Koller S., Vogt S., Al-Masoudi A., Dörscher S., Herbers S., Häfner S., Sterr U., Lisdat C., Denker H., Pizzocaro M., Thoumany P., Rauf B., Clivati C., Levi F., Calonico D., Rlland A., Baynes F. and Margolis H. (2017): First campaigns with PTB transportable optical lattice clock, Verhandlungen der Deutschen Physikalischen Gesellschaft e.V., Q13.4, Vortrag, Mainz, 06 March, 2017 more

Denker H. (2016): A new European Gravimetric (Quasi)Geoid EGG2015, First Joint Comm. 2 and IGFS Meeting, Internat. Symp. on Gravity, Geoid and Height Systems 2016, GGHS2016, Thessaloniki, Greece, 19 – 23 September, 2016

Denker H. (2016): A new European gravimetric (quasi)geoid EGG2015, 1st Joint Commission 2 and IGFS Meeting, International Symposium on Gravity, Geoid and Height Systems 2016, GGHS2016, Thessaloniki, Greece, Sept. 19-23, 2016

Denker H., Timmen L. and Voigt C. (2016): Gravity potential for optical clock comparisons, Optical clocks: quantum engineering and international timekeeping, Workshop, Joint EMRP project consortia: ITOC & QESOCAS, University of York, UK, 08 April, 2016

Denker H., Timmen L. and Voigt C. (2016): Gravity field modelling with regard to optical clock comparisons, First Joint Comm. 2 and IGFS Meeting, Internat. Symp. on Gravity, Geoid and Height Systems 2016, GGHS2016, Thessaloniki, Greece, 19 – 23 September, 2016

Denker H., Timmen L. and Voigt C. (2016): Geodetic contributions to the project “International Timescales with Optical Clocks (ITOC)", First Joint Comm. 2 and IGFS Meeting, Internat. Symp. on Gravity, Geoid and Height Systems 2016, GGHS2016, Thessaloniki, Greece, 19 – 23 September, 2016

Denker H., Timmen L. and Voigt C. (2016): Gravity field modelling with regard to optical clock comparisons, 1st Joint Commission 2 and IGFS Meeting, International Symposium on Gravity, Geoid and Height Systems 2016, GGHS2016, Thessaloniki, Greece, Sept. 19-23, 2016

Lin M. and Denker H. (2016): Comparison of various methods for modeling gravitational effects of the topography, First Joint Comm. 2 and IGFS Meeting, Internat. Symp. on Gravity, Geoid and Height Systems 2016, GGHS2016, Thessaloniki, Greece, 19 – 23 September, 2016

Margolis H. S., Benkler E., Calonico D., Denker H., Delva P., Godun R. M., Lisdat C., Abgrall M., Achkar J., Al-Masoudi A., Barwood G. P., Baynes F. N., Baynham C. F. A., Bilicki S., Bize S., Bookjans E., Bowden W., Cerretto G., Chupin B., Clivati C., Donnellan S., Dörscher S., Fordell T., Gerginov V., Gersl J., Gill P., Grebing C., Guéna, J., Häfner S., Hill I. R., Hobson R., Huang G., Huntemann N., Jones J.M., Kind S. A., Klein H. A., Lamb A., Le Coq Y., Le Targat R., Leute J., Lindvall T., Lipphardt B., Lodewyck J., Menchetti M., Merimaa M., Mura A., Nicoldi D., Nisbet-Jones P. B. R., Ozimek F., Peik E., Pizzocaro M., Piester D., Riedel F., Robyr J.-L., Rolland A., Rosenbusch P., Rovera D., Rust F., Sanner C., Sesie I., Shemar S. L., Shi C., Sterr U., Szymaniec K., Tamm C., Timmen L., Vogt S., Voigt, C. Wallin A. E., Weyes S. and Whibberley P.B. (2016): Towards international timescales with optical clocks, First Joint Comm. 2 and IGFS Meeting, Internat. Symp. on Gravity, Geoid and Height Systems 2016, GGHS2016, Thessaloniki, Greece, 19 – 23 September, 2016

Voigt C., Denker H. and Timmen L. (2016): Time-variable components of the gravity potential field, Optical clocks: quantum engineering and international timekeeping, Workshop, Joint EMRP project consortia: ITOC & QESOCAS, University of York, UK, 08 April, 2016

Denker H. (2015): Gravity potential for optical clocks, Lecture, OCS2015, 1st School on Optical Clocks, Torino, Italy, 29 June – 03 July, 2015

Lin M., Denker H. and Müller J. (2015): Regional gravity field modeling using a two-step point mass method applied to the IAG JSG0.3 test data, Abstract G02p-412, XXVI General Assembly of the International Union of Geodesy and Geophysics (IUGG), Earth and Environmental Sciences for Future Generations, Prague, Czech Republic, 22 June – 02 July, 2015

Margolis H. S., Benkler E., Calonico D., Denker H., Delva P., Godun R. M., Lisdat C., Achkar J., Bize S., Gersl J., Gill P., Lindvall T., Merimaa M., Pizzocaro M., Piester D., Riedel F., Sesia I., Shemar S. L., Sterr U., Timmen L., Voigt C., Vogt S., Weyers S. and Whibberley, P. B. (2015): ITOC: international timescales with optical clocks, Abstract Book, 2015 Joint Conference of the IEEE International Frequency Control Symposium & European Frequency and Time Forum, Denver, Colorado, USA, 12 - 16 April, 2015

Margolis H. S., Benkler E., Calonico D., Denker H., Delva P., Godun R. M., Lisdat C., Gersl J. and Merimaa M. (2015): ITOC: international timescales with optical clocks, Abstract G01p-247, XXVI General Assembly of the International Union of Geodesy and Geophysics (IUGG), Earth and Enviromental Sciences for Future Generations, Prague, Czech Republic, 22 June - 02 July, 2015 more

Margolis H. S., Benkler E., Calonico D., Denker H., Delve P., Godun R. M., Lisdat C., Gersl J, Merimaa M. and members of the ITOC consortium (2015): Towards international timescales with optical clocks, Program and Book of Abstracts, 8th Symposium on Frequency Standards and Metrology 2015, Potsdam, Germany, 12 – 26 October, 2015

Voigt C., Denker H. and Timmen L. (2015): Investigation of time-variable components of the gravity potential for optical clock comparisons, Abstract G02p-423, XXVI General Assembly of the International Union of Geodesy and Geophysics (IUGG), Earth and Environmental Sciences for Future Generations, Prague, Czech Republic, 22 June – 02 July, 2015