Oscillations, Waves, and Interactions - GWDG

292 Schreiber
Beamwalk [µm]
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
horizontal
vertical
0.0
0.0 0.5 1.0 1.5 2.0 2.5
Time [days]
Figure 10. Example of the measured beam wander as obtained at corner 1. Within a
factor of two vertical and horizontal excursions are roughly of the same magnitude.
Earth rotation to produce a constant Sagnac frequency, with a variation of 1 mHz or
less. However the measurements show an overall downward trend and superimposed
systematic excursions of considerable amplitude, where some occur rather sharply,
while others are following a much smoother course. Some of these departures from
the value of Earth rotation are due to variations of the scale factor as a function of
time while others are caused by internal processes in the laser cavity.
From the instantaneous beam postions recorded by the cameras the geometrical
variation in area and perimeter can be computed via an ABCD-Matrix approach.
Figure 12 shows the result. One can see that the area is changing at the parts
per million level, certainly a considerable effect. The simultaneously displayed time
∆f [mHz]
5
0
-5
-10
-15
-20
-25
0 4 8 12 16
Time [days in 2006]
Figure 11. Time series of the drift of the raw measurements of Earth rotation obtained
from the UG2 gyroscope.