Investigation of sub-daily and episodic variations of Earth rotation observed by VLBI, ring laser gyroscopes and GNSS
Zusammenfassung der Projektergebnisse
The goal of the project SPEED was to improve our understanding of the high frequency and episodic variations in the rotation of the Earth. In order to investigate these effects we first needed to obtain accurate time series of the Earth rotation parameters (ERP) with high temporal resolution. We estimated the ERP from the space geodetic techniques VLBI and GNSS, as well as observations from ring laser gyroscopes. A lot of progress has been made towards finding the best analysis strategies for the different techniques. For example, we have investigated the effects of radio source position errors in VLBI. We have also developed methods for combining the different ERP time series. Here, one highlight was the successful combination of VLBI and ring laser data at the normal equation level. The benefit of such a combination is currently limited since only one ring laser with high enough accuracy exists, the “G” ring laser in Wettzell. However, simulations have shown that if data of a global network of ring lasers were available there would be a significant improvement in the accuracy compared to the ERP estimated from VLBI data only. Thus ring lasers have the potential to become an important technique for measuring Earth rotation in the future. Kalman filters for combination of hourly ERP for different techniques at the results level were also developed. These Kalman filters were successfully tested by combining ERP from GNSS and VLBI during the continuous VLBI campaigns of the years 2002, 2005, 2008, and 2011. The high frequency ERP time series were applied for estimation of sub-diurnal tidal ERP models. Models derived from GNSS data were compared with models derived from VLBI data. It was found that it is difficult to estimate the tidal coefficients from GNSS data at certain frequencies due to the difficulty to separate the effects of Earth rotation and the effects of the satellite orbits on the GNSS observations. Combined tidal models based on both GNSS and VLBI data were also calculated. The resulting tidal coefficients were compared to those predicted by ocean tide models and libration, i.e. the IERS sub-diurnal ERP model. We concluded that the IERS model contains significant errors – probably because it is based on an old ocean tide model – and it needs to be updated. We have also studied the different geophysical causes for sub-diurnal ERP variations. In particular we have looked at the excitations caused by the atmosphere. Atmospheric angular momentum estimated from different numerical weather models have been investigated and compared to the observed ERP excitations. Another focus was placed on the excitation of Earth rotation caused by earthquakes. Careful modelling of the excitations caused by earthquakes have been made. We have found that the earthquakes of the last 35 years should have changed the mean position of the pole by about 10 mas towards 120°E and shortened the length of day by about 10 μs. Most of this effect are caused by the largest earthquakes (magnitude >8.5). We have tried to detect these changes in the ERP measurements, however, the effect of one single Earthquake is too small compared to the accuracies of the measurements and the modelling of other geophysical excitations of Earth rotation.
Projektbezogene Publikationen (Auswahl)
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The instantaneous Earth Rotation - still inaccessible? Österreichische Zeitschrift für Vermessung und Geoinformation
(VGI), Vol. 95. 2007, Issue 2, pp. 113–120.
P. J. Mendes Cerveira, R. Weber, H. Schuh
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The ”G” ring laser in Wettzell, Germany, as an indicator for astronomical and geophysical disturbances of the planet Earth. In: H. K. Kaiser and R. Kirner (eds), Proceedings of the Junior Scientist Conference Vienna, Austria, 2008, pp. 291–292.
L. Plank, P. J. Mendes Cerveira
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Earth rotation observed by very long baseline interferometry
and ring laser. Pure and Applied Geophysics, Vol. 166. 2009, Issue 8–9, pp 1499–1517.
P. J. Mendes Cerveira, J. Boehm, H. Schuh, T. Klügel, A. Velikoseltsev, K. U. Schreiber, A. Brzezinski
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Earth rotation parameters from very long baseline interferometry and
ringlaser observables. In: K. Satake, editor, Advances in Geosciences, Vol. 13: Solid Earth, 2009, pp. 155–165.
P. J. Mendes Cerveira, H. Spicakova, H. Schuh, T. Klügel, K. U. Schreiber, A. Velikoseltsev
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Earth rotation. In: G. Xu, (ed.) Sciences of Geodesy I: Advances
and Future Directions, Springer, 2010, chapter 6, pp. 185–227.
F. Seitz, H. Schuh
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Sub-diurnal Earth rotation variations observed by VLBI.
Artificial Satellites, Vol. 45, Issue 2 (Jun 2010): Proceedings of the IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009, pp. 49–55.
T. Nilsson, J. Böhm, H. Schuh
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Subdiurnal variations in the Earth’s rotation from continuous Very Long Baseline Interferometry campaigns. Journal of Geophysical Research: Solid Earth, Vol. 115.2010, Issue B5, B05404.
T. Artz, S. Böckmann, A. Nothnagel, P. Steigenberger
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Assessment of Periodic Sub-diurnal Earth Orientation Parameter Variations at Tidal Frequencies via Transformation of VLBI Normal
Equation Systems. Journal of Geodesy, Vol. 85. 2011, Issue 9, pp 565–584.
T. Artz, S. Tesmer, A. Nothnagel
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Earth rotation. In: Gupta H.K. (eds) Encyclopedia of Solid Earth Geophysics. Encyclopedia of Earth Sciences Series, Springer, 2011, pp. 123–129.
H. Schuh, S. Böhm
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High-resolution atmospheric angular momentum functions related to Earth rotation parameters during CONT08. Journal of Geodesy, Vol. 85. 2011: 425.
M. Schindelegger, J. Böhm, D. Salstein, H. Schuh
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Universal time from VLBI single-baseline observations
during CONT08. Journal of Geodesy, Vol. 85. 2011, Issue 7, pp 415–423.
T. Nilsson, J. Böhm, H. Schuh
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Combining VLBI and ring laser observations for determination of high frequency Earth Rotation variation. Journal of Geodynamics, Vol. 62. 2012, pp. 69-73.
T. Nilsson, J. Böhm, H. Schuh, U. Schreiber, A. Gebauer, T. Klügel
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Methodology for the combination of sub-daily Earth rotation from GPS and VLBI observations. Journal of Geodesy, Vol. 86. 2012, Issue 3, pp 221–239.
T. Artz, L. Bernhard, A. Nothnagel, P. Steigenberger, S. Tesmer
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The new Vienna VLBI software. In: S. Kenyon, M. C. Pacino, and U. Marti (eds) Geodesy for Planet Earth. International Association of Geodesy Symposia, Buenos Aires, Argentina, number 136. 2012, pp. 1007–1011, Springer
J. Böhm, S. Böhm, T. Nilsson, A. Pany, L. Plank, H. Spicakova, K. Teke, H. Schuh
