On the Influence of Diurnal and Subdiurnal Signals in the Normal Vector on Large Ring Laser Gyroscope Observations

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.

Geodesy and Cartography

“…So far there is only one instrument, the G-ring at the Wettzell Observatory in Germany, which has sufficient sensitivity for this purpose, but according to our knowledge other instruments are under construction. Tercjak et al (2015) investigated the application of RLG for estimation of nutation rates. They considered one instrument with parameters of G-ring, but also simulated results from several RLG's and their combination with actual VLBI data.…”

Possible Tests of Fundamental Physics with GINGER

“…As we will discuss in the following, the angular velocity vector, in principle, contains effects due to gravitational theories other than general relativity (GR), such as those related to Lorentz violation in the framework of standard model extension (SME). The kinematic local and global contributions are derived from geophysics and geodesy, as polar motion and tides [10], and, thanks to the very high sensitivity of RLGs, the sub-daily component of the length of day (LOD) is expected to be measurable. These kinematic terms are continuously monitored by the International Earth Rotation System (IERS) [11,12] with very high accuracy; therefore, gravitational theories can be tested by comparing the independent measurements of RLGs and IERS.…”

“…The experimental setup plays an important role, since the response depends on the geometry, and it is necessary to avoid spurious rotations of the apparatus induced by environmental disturbances. The first working RLGs were based on monolithic structures made of very low thermal expansion ceramic materials, and most of the small sized gyroscopes were monolithic [10]. This choice is quite challenging in terms of cost and space.…”