TIDALLY INDUCED SAGNAC SIGNAL IN A RING LASER

The Earth rotation vector is an integral dynamical quantity of the Ear th system, with Earth rotation variations depending on the overall dyn amics of the Earth system at all time scales. New observations of Eart h rotation variations with a precision better than 10(-9) of the Earth rotation would contribute to the understanding of many geophysical ph enomena. High precision short-term observations of the projection of t he Earth rotation vector Omega(E) on the area vector A of a ring laser are now possible. Tidally induced Sagnac effects are due to changes i n the ring geometry (areal strain and perimeter variations), changes i n the normal vector of the ring laser plane (tilt), and the vorticity of the Earth's tidal deformations. Here we estimate the latitude-depen dent effect of the Earth's body tide deformations due to vorticity and tilt. At mid-latitudes, the vorticity delta Omega is of the order 8.1 0(-8)Omega(E), but because it is in the local horizontal plane, it is not detectable by a horizontal ring. The Sagnac effect due to tidal ti lt for a horizontal ring at mid-latitudes is of the order of 4.10(-8) of the Earth rotation effect. Thus, the tidal signal is of an order of magnitude where it may be used for validation of existing and future ring lasers.