In autumn 2007 the superconducting gravimeter GWR C025 was transferred from Vienna (VI) to the new Conrad observatory (CO) 60 km SW of Vienna. It is one of few instruments which were operated at different stations. This aspect motivated a reanalysis of all calibration experiments at VI and CO, focused on drift and noise effects. Considering the drift even of absolute gravimeters in a common adjustment reduces the root mean square error of the averaged calibration factor essentially. Also spring type gravimeters have some potential to contribute to the SG calibration factor determination. The calibration factor of GWR C025 did not significantly change during the transfer from VI to CO. The final calibration factor is calculated as weighted average over in total 9 JILAg and FG5 experiments with an accuracy of better than 0.5‰. The calibration factor is temporarily stable with maximum variation less than 0.1‰. Based on these results the gravity time series of VI and CO have been analyzed. The respective amplitude factors for O1, K1, and M2 agree almost perfectly at both stations after correcting for ocean loading effects. The maximum deviation from the numbers provided by the nonhydrostatic-body-tide models DDW and MAT01 is 0.8‰. 1. Introduction Currently, the superconducting gravimeter (SG) is the most precise instrument for investigating temporal gravity variations both in the time and the frequency domain. SGs exhibit an extremely small instrumental drift that can be modeled by either a linear or exponential function of time [1]. The superconducting gravimeter GWR C025 has been operating since 1995. For more than 12 years it was installed in an underground laboratory in Vienna (Austria) and moved to the new Conrad observatory (CO) 60？km SW of Vienna (VI) in autumn 2007 (Figure 1). Both stations are located at the NE margin of the Eastern Alps. VI is situated at the transition from the Eastern Alps to the Vienna Basin at about 190？m altitude, while CO is located within the mountains at 1045？m. The SG sphere could be kept levitated during transport. Consequently only minor readjustment measures were required, among others because of the gravity difference between both sites. Figure 1: Location of SG sites in Vienna (VI: 48.2489°N, 16.3565°E, 192.74？m a.s.l.) and Conrad observatory (CO: 47.9283°N, 15.8598°E, 1044.12？m a.s.l.) (maps modified after http://commons.wikimedia.org/wiki/Category:Maps). The gravity time series in CO currently extends over more than 4 years and allows now safely comparing the tidal analysis results for VI and CO as well as
References
[1]
M. Van Camp and O. Francis, “Is the instrumental drift of superconducting gravimeters a linear or exponential function of time?” Journal of Geodesy, vol. 81, no. 5, pp. 337–344, 2007.
[2]
V. Dehant, P. Defraigne, and J. M. Wahr, “Tides for a convective Earth,” Journal of Geophysical Research B, vol. 104, no. 1, pp. 1035–1058, 1999.
[3]
P. M. Mathews, “Love numbers and gravimetric factor for diurnal tides,” Journal of the Geodetic Society of Japan, vol. 47, no. 1, pp. 253–259, 2001, in Proceedings of the 14th International Symposium on Earth Tides.
[4]
J. Hinderer, N. Florsch, J. Makinen, H. Legros, and J. E. Faller, “On the calibration of a superconducting gravimeter using absolute gravity measurements,” Geophysical Journal International, vol. 106, no. 2, pp. 491–497, 1991.
[5]
O. Francis, T. M. Niebauer, G. Sasagawa, F. Klopping, and J. Gschwind, “Calibration of a superconducting gravimeter by comparison with an absolute gravimeter FG5 in Boulder,” Geophysical Research Letters, vol. 25, no. 7, pp. 1075–1078, 1998.
[6]
J. Hinderer, M. Amalvict, O. Francis, and J. M？kinen, “On the calibration of superconducting gravimeters with the help of absolute gravity measurements,” in Proceedings of the 13th International Symposium on Earth Tides, B. Ducarme and P. Paquet, Eds., pp. 557–564, Brussels, Belgium, July 1997.
[7]
O. Francis and T. Van Dam, “Evaluation of the precision of using absolute gravimeters to calibrate superconducting gravimeters,” Metrologia, vol. 39, no. 5, pp. 485–488, 2002.
[8]
B. Meurers, “Superconducting gravimetry in geophysical research today,” Journal of the Geodetic Society of Japan, vol. 47, pp. 300–307, 2001.
[9]
J. Hinderer, D. Crossley, and R. J. Warburton, “Gravimetric methods—superconducting gravity meters,” in Treatise on Geophysics, G. Schubert and T. Herring, Eds., vol. 3, pp. 65–122, Geodesy, 2009.
[10]
S. Rosat, J. P. Boy, G. Ferhat et al., “Analysis of a 10-year (1997–2007) record of time-varying gravity in Strasbourg using absolute and superconducting gravimeters: new results on the calibration and comparison with GPS height changes and hydrology,” Journal of Geodynamics, vol. 48, no. 3–5, pp. 360–365, 2009.
[11]
U. Riccardi, S. Rosat, and J. Hinderer, “On the accuracy of the calibration of superconducting gravimeters using absolute and spring sensors: a critical comparison,” Pure and Applied Geophysics, vol. 169, no. 8, pp. 1343–1356, 2012.
[12]
O. Francis and M. Hendrickx, “Calibration of the LaCoste-Romberg 906 by comparison with the superconducting gravimeter C021 in Membach (Belgium),” Journal of the Geodetic Society of Japan, vol. 47, no. 1, pp. 16–21, 2001.
[13]
M. S. Bos and G. H. Scherneck, free ocean tide loading provider, http://froste.oso.chalmers.se/loading/.
[14]
B. Ducarme, “Limitations of high precision tidal prediction,” in Proceedings of the New Challenges in Earth Dynamics (ETS '08), Bulletin d'Informations Marées Terrestres, 145, pp. 11663–11677, 2009.
[15]
B. Ducarme, S. Rosat, L. Vandercoilden, J. Q. Xu, and H. P. Sun, “European tidal gravity observations: comparison with earth tide models and estimation of the Free Core Nutation (FCN),” in Proceedings of the IAG General Assembly: Observing our Changing Earth, M. G. Sideris, Ed., vol. 133, pp. 523–532, International Association of Geodesy, Perugia, Italy, July 2007.
[16]
B. Meurers, “Aspects of gravimeter calibration by time domain comparison of gravity records,” Bulletin D'Informations Marées Terrestres, vol. 135, pp. 10643–10650, 2002.
[17]
C. Kroner, “Hydrological signalsin the SG records at Moxa—a follow-up,” Bulletin D'Informations Marées Terrestres, vol. 142, pp. 11353–11358, 2006.
[18]
B. Meurers, M. Van Camp, and T. Petermans, “Correcting superconducting gravity time-series using rainfall modelling at the Vienna and Membach stations and application to Earth tide analysis,” Journal of Geodesy, vol. 81, no. 11, pp. 703–712, 2007.
[19]
Y. Imanishi, T. Higashi, and Y. Fukuda, “Calibration of the superconducting gravimeter T011 by parallel observation with the absolute gravimeter FG5 #210—a Bayesian approach,” Geophysical Journal International, vol. 151, no. 3, pp. 867–878, 2002.
[20]
Y. Tamura, T. Sato, Y. Fukuda, and T. Higashi, “Scale factor calibration of a superconducting gravimeter at Esashi Station, Japan, using absolute gravity measurements,” Journal of Geodesy, vol. 78, no. 7-8, pp. 481–488, 2005.
[21]
B. Iglewicz and D. C. Hoaglin, “How to detect and handle outliers,” in The ASQC Basic References in Quality Control: Statistical Techniques, E. F. Mykytka, Ed., vol. 16, American Society for Quality Control (ASQC), Statistics Division, ASQC Quality Press, Milwaukee, Wis, USA, 1993.
[22]
B. Meurers and D. Ruess, “Errichtung einer neuen Gravimeter-Eichlinie am Hochkar,” ？sterreichische Zeitschrift für Vermessungswesen und Photogrammetrie und Photogrammetrie, vol. 73, no. 3, pp. 175–183, 1985.
[23]
B. Meurers and D. Ruess, “Gravity measurements at the Hochkar calibration line (HCL),” ？sterreichische Beitr？ge zu Meteorologie und Geophysik, vol. 26, pp. 209–215, 2001, Proceedings of the 8th International Meeting on Alpine Gravimetry, Leoben, Austria, 2000.
[24]
SCINTREX Limited, “CG5 Scintrex Autograv system operation manual,” part # 867700 Rev. 1, pp. 312, 2006.
[25]
W. H. Press, S. A. Teukolsky, W. T. Vetterling, and B. P. Flannery, Numerical Recipes in Fortran, the Art of Scientific Computing, Cambridge University Press, Cambridge, Mass, USA, 2nd edition, 1992.
[26]
H. G. Wenzel, “Precise instrumental phase lag determination by the step response method,” Bulletin D'Informations Marées Terrestres, vol. 111, pp. 8032–8052, 1991.
[27]
H. G. Wenzel, “The nanogal software: earth tide data processing package ETERNA 3.30,” Bulletin D'Informations Marées Terrestres, vol. 124, pp. 9425–9439, 1996.
[28]
M. Van Camp and P. Vauterin, “Tsoft: graphical and interactive software for the analysis of time series and Earth tides,” Computers and Geosciences, vol. 31, no. 5, pp. 631–640, 2005.
[29]
Y. Tamura, “A harmonic development of the tide-generating potential,” Bulletin D'Informations Marées Terrestres, vol. 99, pp. 6813–6855, 1987.
