On the occasion of the fourth International Comparison of Absolute Gravimeters carried out at Sèvres in 1994 an extensive series of microgravimetric measurements was organized. In total, fifteen LaCoste, four Scintrex CG-3M and one Sodin gravimeter measured, within a small network, vertical gravity gradients and a calibration baseline. The results show that the accuracy for single instruments is in the range of 3 μGal to 5 μGal in gravity difference, for the Scintrex and the LaCoste meters. Data from the series were also used to intercompare different ways of calibrating the gravimeter electrostatic feedback systems. The calibration platform of the Institut für Angewandte Geodäsie, (IFAG), Frankfurt, and the calibration lift of the Observatoire Royal de Belgique (ORB) were installed at Sèvres and the results compared with those for the calibration line. This paper gives the first results and a review of the techniques used.

Gravimeter

10.1088/0026-1394/32/3/002

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An Introduction to the use of HICUM for Signal Analysis

M. van Ruymbeke Rachelle Rose Howard E. Pütz André Somerhausen P. Barriot

This paper introduces a novel method for signal analysis whereby a weak signal can be detected in a noisy environment, providing the time period is known. The time period for each earth tide signal is found using the Doodson argument. Each cycle is then divided into sectors and a histogram of the data is plotted. The histograms for all the cycles are then stacked to produce the cumulative effect, hence the name for the method is HiCum . The paper uses synthetic data to demonstrate the ability of the technique to detect a signal in a noisy environment. Some of the additional benefits of the method over spectrum analysis are shown using field data from EDAS. There is also a section which gives some practical guidance on how to use HiCum with mDAS Grapher.

SIGNAL (programming language)

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On gravity measurements related with the november 3, 1994 solar eclipse in Brazil

Sílvio Rogério Correia de Freitas M Van Ruymbere B. Ducarme André Somerhausen Marta Sílvia Maria Mantovani

Solar eclipse

Eclipse

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Projects of the Royal Observatory of Belgium (ROB) at the Lanzarote Geodynamical Laboratory (LGL)

測地学会誌 (2001)

M. van Ruymbeke André Somerhausen B. Ducarme Ricardo Vieira José Arnoso

A series of experiments prepared at the Royal Observatory of Belgium, are running in the three Lanzarote laboratories under the EDAS concept (van Ruymbeke et al. ,1993,1997a). The main purposes of our observations which started ten years ago (Fernandez et al., 1990), cover the domains of the tidal effects including oceanic tides interactions, ground deformation and environmental parameters monitoring. We prepare instruments adapted to the special conditions of volcanic medium in the mind of the EDAS concept which is adapted to that project. In the Timanfaya area, we are observing the interactions between a shallow magma chambers and the tidal signals. A correlation exists between the drift rate of a LaCoste & Rornberg gravimeter and the local seismic activity which seems to induce heat flow changes. In the cave Jameo del Agua, it is possible to record the oceanic tide in excellent conditions due to the filtering of the sea-waves by a few kilometers long siphon connecting the site to the open sea. Original probes are designed to check the long term stability of pressure sensors. A vertical pendulum register the tiit of the ground induced by the oceanic loading. High precision thermometers (van Ruymbeke et al., 1999) assume the monitoring of the vertical thermal gradient which could be influenced by the modulation of the salinity by the water flow from aquifers. The HiCum method is used to detect the admittance between the different parameters.

Gravimeter

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Calibration of gravimeters with the VRR 8601 calibration platform

Metrologia (1995)

M. van Ruymbeke André Somerhausen N Grammatica

At the 1994 International Comparison of Absolute Gravimeters in Sèvres, a platform oscillating vertically with a sinusoidal motion was used to produce defined accelerations which were applied to gravimeters for their calibration. Gravimeters equipped with different types of feedback systems were compared. This allowed an evaluation of filtering effects. A long series of tidal recordings, and a calibration obtained by this platform method, gave tidal factors for the Bureau International des Poids et Mesures (BIPM). Comments on previous recordings are included.

Gravimeter

10.1088/0026-1394/32/3/009

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