Giancarlo D'Agostino

Perturbations of the local gravity field due to mass distribution on precise measuring instruments: a numerical method applied to a cold atom gravimeter

We present a numerical method, based on a FEM simulation, for the determination of the gravitational field generated by massive objects, whatever geometry and space mass density they have. The method was applied for the determination of the self-gravity effect of an absolute cold atom gravimeter which aims at a relative uncertainty of 10−9. The deduced bias, calculated with a perturbative treatment, is finally presented. The perturbation reaches (1.3 ± 0.1) × 10−9 of the Earths gravitational field.

Final report on the Seventh International Comparison of Absolute Gravimeters (ICAG 2005)

The Bureau International des Poids et Mesures (BIPM), S?vres, France, hosted the 7th International Comparison of Absolute Gravimeters (ICAG) and the associated Relative Gravity Campaign (RGC) from August to September 2005.ICAG 2005 was prepared and performed as a metrological pilot study, which aimed: To determine the gravity comparison reference values; To determine the offsets of the absolute gravimeters; and As a pilot study to accumulate experience for the CIPM Key Comparisons. This document presents a complete and extensive review of the technical protocol and data processing procedures. The 1st ICAG?RGC comparison was held at the BIPM in 1980?1981 and since then meetings have been organized every 4 years.In this paper, we present an overview of how the meeting was organized, the conditions of BIPM gravimetric sites, technical specifications, data processing strategy and an analysis of the final results. This 7th ICAG final report supersedes all previously published reports.Readings were obtained from participating instruments, 19 absolute gravimeters and 15 relative gravimeters. Precise levelling measurements were carried out and all measurements were performed on the BIPM micro-gravity network which was specifically designed for the comparison.

Reconstruction of the free-falling body trajectory in a rise-and-fall absolute ballistic gravimeter

Absolute ballistic gravimeters can measure the free-fall acceleration with an uncertainty of few parts in 109. Typically, the vertical trajectory of a test body subjected to the gravity field is tracked using interferometric methods, and a mathematical model of the motion is fitted to the time–position coordinates in a least-squares adjustment. In this paper, we describe a non-linear regression analysis applied to the IMGC-02 transportable gravimeter, developed at the Istituto Nazionale di Ricerca Metrologica (INRIM). We show how the method yields an accurate estimate of the free-fall acceleration avoiding measurement of the vertical gradient.

Uncertainty due to parasitic accelerations in absolute gravimetry

Absolute gravity measurements are based on the reconstruction of the free-falling motion of a test body in vacuum. In this paper, two large disturbing effects are studied, namely the non-gravitational accelerations originated by rotation and translation of the flying body. Their contribution to the uncertainty of the free-fall acceleration is evaluated using the Monte Carlo method as proposed in Supplement 1 to the GUM. The analysis is specifically applied to the IMGC-02 absolute gravimeter, but can be easily extended to other instruments, including cold-atom gravimeters currently under development.

The e-Mass euramet joint research project: The watt balance route towards a new definition of the kilogram

The e-MASS joint research project (JRP) supported by EURAMET gathers several European metrology institutes in the aim to improve existing watt balances and to contribute to a new definition of the mass unit. This paper describes the main technical tasks developed in the framework of the project

Evaluating measurement uncertainty in absolute gravimetry: An application of the Monte Carlo method

Absolute gravity measurements are based on the reconstruction of the free-falling motion of a test body in vacuum. In this paper, two large disturbing effects are studied, namely, the non- gravitational accelerations originated by rotation and translation of the flying body. Their contribution to the uncertainty of the free-fall acceleration is evaluated using the method proposed in Supplement 1 to the GUM. The analysis is specifically applied to the IMGC-02 absolute gravimeter, but can be easily extended to other instruments.

Comparison of 3 absolute gravimeters based on different methods for the e-MASS project

The three INMs involved in the JRP e-MASS project operate three different absolute gravimeters, which rely on three different measurement methods. METAS operates a commercial FG5 gravimeter, INRIM has been developing his own ballistic symmetrical rise-and-fall gravimeter IMGC-2 and LNE-SYRTE develops a cold atom gravimeter. These gravimeters are briefly described in this paper and their differences and performances are discussed. The results of a comparison performed at the LNE laboratory will be presented.

Uncertainty Propagation in a Non-linear Regression Analysis: Application to a Ballistic Absolute Gravimeter (IMGC-02)

Todays most accurate measurements of the gravitational acceleration are based on interferometric reconstruction of the vertical trajectory followed by a test body launched in a vacuum chamber. The gravity value g is one of the parameters of a model function derived from the law of motion of the body, and is estimated by a least squares adjustment. In this paper we present the regression analysis applied to the IMGC-02 absolute gravimeter and the associated uncertainty propagation We also show how a suitable choice of the reference height z, at which g is calculated, can yield a minimum-variance estimate. This choice is based on the covariance matrix of the parameter estimates provided by the adjustment algorithm.

Long term plumb-line alignment of precise measuring instruments: an adaptive digital controller designed for an autoleveling platform.

Plumb-line alignment can affect the sensors of precise scientific instruments. When its effect is one of the main contributors to the measurement uncertainty, the deviation from the true vertical must be continuously monitored or compensated. This paper describes a digital control system designed and tested for an autoleveling platform. Best performances are obtained with an adaptive digital compensator based on a convolution of the error signal. Although accuracy and resolution of the leveling transducer limit the ultimate sensitivity, laboratory tests showed that the controller kept for several hours the base-plate top within ±1 μrad. These performances are suitable for maintaining the alignment of relative spring gravimeters used by volcanologists in long-term gravity measurements.