On the Influence of Diurnal and Subdiurnal Signals in the Normal Vector on Large Ring Laser Gyroscope Observations
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Pure and Applied Geophysics
On the Influence of Diurnal and Subdiurnal Signals in the Normal Vector on Large Ring Laser Gyroscope Observations MONIKA TERCJAK,1 ANDRE´ GEBAUER,2 MARCIN RAJNER,1,3 ALEKSANDER BRZEZIN´SKI,1,4 and KARL ULRICH SCHREIBER2 Abstract—The ring laser gyroscope (RLG) technique has been investigated for over 20 years as a potential complement to space geodetic techniques in measuring Earth rotation. However, RLGs are also sensitive to changes in their terrestrial orientation. Therefore in this paper, we review how the high-frequency band (i.e. signals shorter than 0.5 cycle per day) of the known phenomena causing site deformation contribute to the RLG observable, the Sagnac frequency. We study the impact of solid Earth tides, ocean tidal loading and non-tidal loading phenomena (atmospheric pressure loading and continental hydrosphere loading). Also, we evaluate the differences between available models of the phenomena and the importance of the Love numbers used in modeling the impact of solid Earth tides. Finally, we compare modeled variations in the instrument orientation with the ones observed with a tiltmeter. Our results prove that at the present accuracy of the RLG technique, solid Earth tides and ocean tidal loading effects have significant effect on RLG measurements, and continental hydrosphere loading can be actually neglected. Regarding the atmospheric loading model, its application might introduce some undesired signals. We also show that discrepancies arising from the use of different models can be neglected, and there is almost no impact arising from the use of different Love numbers. Finally, we discuss differences between data reduced with tiltmeter observations and these reduced with modeled signal, and potential causes of this discrepancies. Keywords: Ring laser gyroscope, Sagnac frequency, solid Earth tides, ocean tidal loading, non-tidal loading effects, Love numbers.
1 Faculty of Geodesy and Cartography, Warsaw University of Technology, Pl. Politechniki 1, 00-661 Warsaw, Poland. E-mail: [email protected] 2 Technical University of Munich, Research Unit Satellite Geodesy, Arcisstr. 21, 80333 Munich, Germany. 3 Chalmers University of Technology, 412 96, Gothenburg, Sweden. 4 Space Research Centre, Polish Academy of Sciences, Bartycka 18A, 00-716 Warsaw, Poland.
1. Introduction Ring laser gyroscopes (RLGs) are instruments for measuring absolute rotation. They observe the Sagnac effect, which arises due to a difference in the respective optical path lengths of the counter-propagating laser beams within a cavity (Schreiber and Wells 2013). Although the two beams travel the same path, under the same conditions, they traverse different distances in space due to the sensor rotation. It results in the beat frequency (Sagnac frequency), which is directly proportional to the dot product of the vector normal to the gyroscope plane, and the vector of its rotation (Stedman 1997). For large RLGs firmly tied to the ground, the rotation vector is actually the rotation vector of the Ea
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