Oscillations, Waves, and Interactions - GWDG

298 Schreiber
Δf [µHz]
100
50
0
-50
-100
360 365 370 375
Time [days in 2006]
Figure 18. Time series of the variations of the Earth rotation measuremets of G after the
mean value of the rotation rate has been subtracted.
diagram. While the phase of the theoretical polar motion signal agrees well with the
measurements, there remain small deviations in amplitude. Since the model assumptions
are based on a simplified deformable Earth one may expect that eventually a
better insight into the Earth interior may gained.
However, before this goal can be addressed it is necessary to get a better control
of the different bias mechanisms of large ring lasers, which were mentioned several
times before. While the diurnal polar motion can be understood as a wobble of the
Earth rotation axis, laser gyros also experience tilts from solid Earth tides. These
signals occur at a period of half a siderial day and have amplitudes of up to 40 nrad in
Wettzell. For the ring lasers in Christchurch one can see additional tilts from ocean
loading, which make this effect approximately 3 times larger [21]. Figure 19 shows
a spectrum of the ring laser measurements of G taken without interruption over a
PSD [•10 -12 Hz]
80
60
40
20
0
8 12 16 20 24 28 32
Frequency [µHz]
Δf = 50 nHz
Figure 19. Spectrum of the G ring laser taken from a dataset as long as 243 days. The
major signals for diurnal polar motion and solid Earth tides are clearly visible.