Accurate Determination of the Earth Tidal Parameters at the BIPM to Support the Watt Balance Project

To achieve the targeted accuracy in the Bureau International des Poids et Mesures (BIPM) watt balance (WB) project, the value of g (acceleration due to gravity) must be known to an accuracy of 10⁻⁹ (10 nm/s²) during the operation of balance. Gravity changes due to Earth Tides are the largest time variable signal affecting g at 10⁻⁷. In order to improve the tidal prediction at the BIPM site, the relative spring gravimeter gPhone#032 collected observations for 6 months on site B of the BIPM. An analysis of the tidal results is presented here. We compare them with recent Earth and oceanic loading tidal models. In addition, using the gravity data from the Superconducting Gravimeter in Walferdange we demonstrate that a precision of +/−20 nm/s² can be achieved on the predicted value of g using a synthetic tide and including atmospheric pressure, polar motion and hydrological effects.