On the Influence of Known Diurnal and Subdiurnal Signals in Polar Motion and UT1 on Ring Laser Gyroscope Observations

The ring laser gyroscope (RLG) technique has been investigated for about 20 years as a potential complement to space geodetic techniques in measuring variations of Earth rotation. The technique is of great interest, especially in the context of monitoring rapid changes of rotation with sub-daily resolution. In this paper, we review how the known high frequency signals in Earth rotation parameters, including the so-called diurnal polar motion, diurnal and semidiurnal ocean tide effects in polar motion and UT1 and librations, prograde diurnal in polar motion and semidiurnal in UT1, contribute to the RLG observable, the Sagnac frequency. Our results suggest that at the current accuracy level of the technique, the signals coming from diurnal polar motion and ocean tides should be taken into account in analysis while the influence of libration can be neglected. We also point out that the contributing signals are superimposed upon each other and can hardly be separated from the data from a single instrument. Our computations are done taking parameters of the RLG at the Wettzell Observatory in Germany. However, we also consider how the strength of a particular signal depends on the geographic location of a horizontally mounted instrument. Finally, we discuss the relationship between the geographical location and terrestrial orientation of RLG and its consequence for the observed Sagnac signal.