Relative campaign during the International Comparison of Absolute Gravimeters ICAG-2005 and the strategy data treatment combined with the absolute results

Abstract

As a tradition following the first International Comparison of Absolute Gravimeters in 1981 (Becker and Groten, 1983), during the 7th International Comparison of Absolute Gravimeters (ICAG-2005) at the BIPM (Bureau International des Poids et Mesures), high precision relative gravity ties and vertical gradients were measured over the BIPM ICAG-network which includes sites with a gravity difference up to 9 mGal*. 12 institutes of 10 countries with 15 gravimeters of 6 different types were employed. We report in this paper the organisation of the relative campaign, the raw data analysis, the relative-only measurement adjustment and the combined adjustment of the relative and absolute data. Related problems issued during the measurements and data processing are introduced. When preparing the final version of this paper, the absolute g-values of the ICAG 2005 are not yet available (Vitushkin et al., IGFS2006). In consequence, results presented here are preliminary. The detailed analysis of adjusted g-values and gravimeter calibration etc. will be discussed in a forthcoming paper. The relative gravimetry raw data analysis, the comparison between the relative-only adjustment and the absolute-only adjustment shows that the uncertainty of an adjusted gravity difference given by the relative campaign is of the order of 1~2 $\mu Gal$, probably ±1.3 $\mu Gal$, and that of the gradient is of the order of 1~2 $\mu Gal$/m.