Gravimetric factors in Brazil for a model of anelastic Earth

Abstract

Geodetic observations are affected by the disturbing potential of the luni-solar tide. Among those observations, the value of g obtained from gravimetric survey needs correction by the gravimetric factor. This correction is derived from the Numbers of Love, which depend on the adopted model of Earth. Because of this, it is necessary to update the correction since the gravimetric factor widely used in Brazil as δ = 1.20 does not consider local rheological variations and they are latitude dependent. A discrepancy of about 1% between the observed tidal gravimetric factors δ of the "Trans World Tidal Gravity Profiles" (TWTGP), related to Brussels fundamental station, and those obtained by recent observations reported by Freitas and Ducarme (1991). Experiments based on inertial force effects also reveal a variation of about 0.5% in the observed δ. A same order of magnitude difference is obtained for an anelastic Earth model when compared with a viscous-elastic model and even when different frequencies of tidal perturbations are considered. In this paper regression models are presented for gravimetric factors for the lunar components O_{1 and M2 in Brazil. These models were obtained from observations performed at stations belonging to the Brazilian segment of the TWTGP.}