A new generation of absolute gravimeters

TLDR

The paper describes design improvements in a new generation of absolute gravimeters, the FG5. The FG5 uses a vertically oriented interferometer with an iodine‑stabilized laser, automatic peak detection, and an active Super Spring seismometer to eliminate floor vibration and tilt effects. The new design yields improved isolation, thermal stability, trajectory control, real‑time analysis, robustness, and an instrumental uncertainty of 1.1 × 10⁻⁸ m s⁻² (1 μGal), with device agreement of 1.8 μGal and optimal‑condition standard deviations of 5–8 μGal.

Abstract

We describe the design improvements incorporated in a new generation of absolute gravimeters, the FG5. A vertically oriented (in-line) interferometer design is used to remove the influence of floor vibration and tilt on the optical path length. The interferometer uses an iodine-stabilized laser as a primary length standard, with circuitry for automatic peak detection and locking. The seismic isolation system is an active long-period seismometer (Super Spring). The new design has improved passive isolation and thermal drift characteristics over previous systems. Programming flexibility and control of the test mass trajectory have been improved. The computer system has also improved real-time analysis and system capability. The FG5 instrument has a higher level of robustness, reliability and ease of use. These design advances have led to an instrumental uncertainty estimate of 1,1 × 10-8 m s-2 (1,0 μGal). Instrument agreement among nine similar devices is 1,8 μGal and observations under optimal conditions exhibit standard deviations of 5 μGal to 8 μGal.