Performance of two Scintrex CG3M instruments at the fourth International Comparison of Absolute Gravimeters

Two Scintrex CG3M gravimeters were calibrated and compared with other relative meters (LaCoste-Romberg and Scintrex meters) at the fourth International Comparison of Absolute Gravimeters at Sèvres, France (30 May to 2 June 1994). LaCoste-Romberg meters were used as reference. Three main experiments were carried out at the Bureau International des Poids et Mesures. First, a calibration of the two Scintrex CG3M meters on a new baseline of five points, spanning a range of about 8 mGal. It is shown that both Scintrex meters provide results similar to within 0,005 mGal, even in noisy places, and that Scintrex results are similar to those of LaCoste-Romberg instruments to within an accuracy better than 0,010 mGal. Second, measurements of vertical gradient at four points were carried out. The results for the Scintrex meters lie within 0,007 mGal/m and are similar to those of LaCoste-Romberg meters to within an accuracy of around 0,010 mGal/m. Third, a series of continuous records (each of about 10 minutes) was carried out with three LaCoste-Romberg and the Scintrex meters at four adjacent points. A repeatability of better than 0,005 mGal was obtained for one Scintrex meter. There is a difference of 0,010 mGal with LaCoste-Romberg data. These results confirm that the Scintrex meter is suitable for measuring small gravity differences, similar to those observed on active volcanoes.