Development of new free-fall absolute gravimeters

Abstract

The design and first results of two free-fall absolute gravimeters are reported: a stationary gravimeter is designed and can be used as a reference system and a portable gravimeter is aimed at field measurements.The determination of the acceleration due to gravity is done interferometrically in both instruments. The whole fringe signal is digitized by a high-speed analogue-to-digital converter, which is locked to a rubidium frequency standard. This fringe recording and processing is novel as compared with commercial free-fall gravimeters, which use an electronic zero-crossing discrimination. Advantages such as the application of a zero-phase-shifting digital filter to the digitized data are depicted. The portable gravimeter's mechanics deviate from the conventional type. Springs are used to accelerate and decelerate the carriage supporting the falling object.A detailed uncertainty budget is given for both gravimeters. The combined standard uncertainty for the portable and for the stationary gravimeter is estimated at 38.8 µGal and 16.6 µGal, respectively. The corresponding statistical uncertainties are 1.6 µGal (over one day of measurement) and 0.6 µGal (over one month of measurement).The different designs and dimensions of the new free-fall gravimeters can help to reveal unknown or so far underestimated systematic effects. The assessments of the uncertainties due to seismic noise and shock vibrations, and electronic phase shifts give validity to this assumption.

Correction due to the finite speed of light in absolute gravimeters

“…• For the symmetric rise-and-fall measurement schemas 17) which follows from the evenness of weighting functions for such schemas [7].…”

Measuring the Newtonian constant of gravitation with a differential free-fall gradiometer: A feasibility study

“…The proposed instrument is based on the principle of a free-fall absolute gravimeter 10,11 (FFAG). In such an FFAG a test mass, which contains a corner cube reflector, is released in a vacuum vessel.…”

“…Since the differential free-fall gradiometer is based on the same measurement principle as a common free-fall absolute gravimeter (it can be considered as a combination of four free-fall absolute gravimeters), we can apply the same analysis made for those instruments (see 10,11 ).…”

Linear ultrasonic motor for absolute gravimeter

“…A precise knowledge of the magnitude of the Earth's gravitation field and its variation is crucial for various aspects of science and technology, [1][2][3]. It can be acquired with a high-precision absolute gravimeter and used for earthquake prediction, exploration of mineral resources and as essential reference for aircraft navigation and missile guidance.…”