Gravity Monitoring Equipment

Contact: Herb.McQueen@anu.edu.au T: +61 2 612 55515

CT031 - A Compact Tidal Superconducting Gravimeter.

Superconducting Gravity Meter

RSES operates a Superconducting Gravimeter at Mt Stromlo Observatory, continuously monitoring small changes in gravity caused by tidal, environmental and seismic effects.

The Mount Stromlo gravimeter is a GWR Instruments manufactured Compact Tidal Superconducting Gravimeter designated CT031. Operating at liquid helium temperatures, the instrument is built around a superconducting niobium sphere levitated in a magnetic field in an evacuated chamber. Gravity fluctuations are determined from changes in the feedback coil current required to precisely centre the sphere in its chamber. The SG is extremely stable over long periods, and therefore ideal for normal mode, tidal and longer period observations.

The new absolute gravimeter operating at Mt Stromlo - FG5#237.

Absolute and Portable Tidal Gravimeters

Through the AuScope program RSES has acquired an FG5 absolute gravimeter and a portable gPhone spring gravimeter for continuous Earth tide recording. The FG5 will be used initially for monitoring the stability of core benchmarks across the Australian continent, providing reference points for ties to sea level monitoring stations, and for instrument calibration while the gPhone will be used to improve the accuracy of ocean tide loading models around Australia.

The Micro-g Lacoste FG5 gravimeter operates by measuring the free fall of a corner cube in a vacuum chamber using a highly stable laser interferomenter and a Rubidium clock. It is capable of 2-3 microgal accuracy in 24 hour site occupations.

The portable tidal gravimeter is a gPhone, also manufactured by Micro-g Lacoste. The gPhone is a metal spring relative gravimeter derived from geophysical survey instruments but specifically optimised for measurements in the tidal frequency band by component screening, improved the temperature stability with double oven controls and better vacuum seals for improved pressure stability. In addition the gPhone is equipped with a precise GPS locked Rubidium clock for accurate timing of the phase of tidal constituents