Installation and First Data Analysis of the Dual Sphere Superconducting Gravimeter at the South African Geodynamic Observatory Sutherland

Abstract

In February 2000 the reconstructed Dual Sphere Superconducting Gravimeter (SG) with two gravity sensors has been installed at the newly constructed South African Geodynamic Observatory Sutherland (SAGOS). Additionally meteorological sensors and a ground water table sensor are installed for estimation of gravity changes induced by the atmosphere and hydrosphere. The quality of the site is discussed according to the requirements for a SG site. The difference of the tilt minima for both sensors is adjusted to about 4.5 nmis2. For both gravity sensors the calibration factors have been determined by comparison with a well calibrated LaCoste & Romberg Gravimeter which records to the SG in parallel. With a recently developed low frequency sine and square wave generator based on a PC a step response experiment has been carried out to determine the transfer function and to calculate the instrumental time lag. The station is remote controlled by a "Multi Media Monitoring Controlling and Information System" (M3CIS) which operates in real time via Internet. The preliminary short period tidal parameters have been determined for both sensors which are in good agreement. An amplitude spectrum presents the gravity residuals. The single atmospheric pressure admittance is determined for both sensors.