Relative Gravity Measurement Campaign during the 8th International Comparison of Absolute Gravimeters (2009)

Abstract

The 8th International Comparison of Absolute Gravimeters (ICAG-2009) and the associated Relative Gravity Campaign (RGC2009) took place at the Bureau International des Poids et Mesures (BIPM) between July and October 2009. Altogether 24 institutes with 22 absolute gravimeters and 9 relative gravimeters participated in the ICAG/RGC campaign. Accurate absolute and relative gravity measurements as well as precision levelling measurements were performed on the micro-gravity 3D-grid at the BIPM. The 2009 comparison was the first to be organized as a Comité International des Poids et Mesures (CIPM)metrological Key Comparison under the CIPM MRA (Mutual Recognition Arrangement), which means that the result will be officially recognized by the governmental organizations responsible. As a consequence, the relative gravimeters employed were carefully selected and the measurement schedules were rigorously enforced compared to earlier campaigns. Thus the quality of the RGC2009 and the determination of the BIPM local gravity network were improved.After thirty years and eight successive ICAGs, the BIPM has decided to transfer its role to the National Metrological Institutes, although the CIPM will continue to organize the key comparison as ICAGs. The background to the RGC2009, and the organization, data processing and final results of the gravity and vertical gravity gradients are presented in this paper. This report is more detailed than previous final reports of the RGCs. Notation ICAG: International Comparison of Absolute Gravimeters RGC: Relative Gravity Campaign organized in association with ICAG AG: absolute gravimeter RG: relative gravimeter KC: CIPM key comparison WB: BIPM watt balance 1 µGal = 10 -8 m s −2 g: measured absolute acceleration due to gravity in µGal (minus a constant value of 980 900 000 µGal) G: adjusted g value KCRV: KC reference value of G δg, δG: differences of g or G H: height in meters above the ground benchmark γ H : average gradient corresponding to the height H RMS: root mean square error given by a least-squares adjustment (1-σ statistic estimation) Mean: mean value of a data set Std: standard deviation u: standard uncertainty Site, Station and point: The BIPM gravity network comprises indoor and outdoor relative measurement ties between 5 sites (A, B, C1, C2 and WB) and 12 stations (Figures 2.2.1, A, B, B1-B6, C1, C2, W1 and W2). The WB site is used for the BIPM watt balance project. Results at the WB site are not discussed in this paper. This paper therefore is limited to 4 sites and 10 stations. At each station, 3 points are defined at 0.30 m, 0.90 m and 1.30 m above the ground benchmark (C1 and C2 have only 2 points at 0.90 m and 1.30 m). There are 28 points in total. Naming convention is by station plus height in cm, e.g. A.030, A.090 and A.130.

A Determination of the Local Acceleration of Gravity for the NIST-4 Watt Balance

“…The determination of gravity for NIST-4 follows that of more thorough evaluations of gravity of other watt balance efforts [5][6][7][8] . Ties (the difference in gravity between two points) were measured between absolute measurement locations and the horizontal-plane position of the NIST-4 test mass along the vertical concentric symmetry axis of the permanent magnet used to generate the magnetic field for NIST-4.…”

Détermination de l’accélération de la pesanteur pour la balance du watt du LNE

“…Il est dénommé « S105 », en référence à son numéro de série, durant les campagnes de mesures relatives (RGC 2 ) [14,15] précédemment liées aux comparaisons internationales de gravimètres absolus (ICAG 3 ).…”

Towards the measurement of zero vertical gradient of gravity on the Earth’s surface

“…During tower measurements we have to maintain a certain vertical distance between the measured points or levels, which seems to become stabilized recently on about 1 m. For instance Jiang et al (2012) measured gravity at heights of 0.3 m, 0.9 m and 1.3 m; Breili and Rolstad (2009) observed the change in gravity over vertical distance of 1.2 m; Hunt et al (2002) used 1 m; Csapó and Völgyesi (2002) measured at three levels, namely Fig. 5) as a function of the vertical distance h between the cone apex itself and the other calculating point either just above (dots) or below (crosses) the cone apex, respectively.…”