Fróðskaparrit - 01.01.1975, Blaðsíða 32

40
Earth Tides
demonstrated. This is of particular importance with respect
to the liquid core dynamical effects (see § 6).
A similar relation must exist between the Moon’s librations
and the tidal deformations of the Moon.
The determination of the irregularities of the rotation of
the Earth, including the polar motion, derived from doppler
tracking of satellites, laser measurements of the Earth-Moon
distance or by very long base interferometry implies a very
precise determination of the total earth tide.
On the other hand the phase lag of the semi-diurnal sec-
torial earth tides is a basic factor producing the secular
retardation of the Earth’s rotation and it is a parameter
representative of the Earth’s viscosity (see § 6).
There is now some hope that we could be able to derive it
in the next ten years.
2. Space Dynamics
a) The perturbing effects of tidal variations of the Earth
potential on artificial satellite orbits have been derived
from the observations themselves by R. Newton and by
Y. Kozai. They amount to as much as 50 meters on a
satellite position.
b) As laser distance measurements to the Moon and satel-
lites will have ratings of some centimeters and as the
radial tidai deformation reaches an amplitude of 30 to
40 cm, the latter must be taken into account. But (as
reported by J. Derral Mulholland to Cospar) a simple
analytical elastic earth-model being insufficient to
calculate exactly this tidal deformation, experimental
measurements are necessary at the sites concerned.
3. Gravimetry
Absolute determinations of g are made now with a pre-
cision of nearly one microgal (10^9) (Sakuma, Faller). The
comparison of such determinations made at different sites