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Abstract

The International Geodynamics and Earth Tide Service (IGETS) was established in 2015 by the International Association of Geodesy (IAG). IGETS continues the activities of the Global Geodynamics Project (GGP, 1997-2015) to provide support to geodetic and geophysical research activities using superconducting gravimeter (SG) data within the context of an international network. In 2014 December the Royal Observatory of Belgium installed the iGrav #019 at the surface site of the Rochefort "Lorette" cave laboratory. The Lorette cave is one of several cavities that belong to the Wamme–Lomme karst system, a 10 km long karst area. At the surface of the site, a small and solid building, located at the border of a large sinkhole, hosts the gravity laboratory, which is thermally stabilized at ~25°C by a heater, excepted during a few days each summer when the temperature may increase above that level. The iGrav #019 is installed directly on the bedrock (limestone) in a 1 m deep shaft. Two meters away from the iGrav there is a pillar of cement (60% sand, 40% cement, no iron nor stones) founded 1 meter deep on the bedrock and on which absolute gravity measurements are performed 10 times or more per year with the FG5#202 absolute gravimeter. See description in Fig A7 in Van Camp et al., 2017. As this instrument was installed among others to investigate flash floods in the caves, it regularly monitors sudden changes in gravity reaching 50-100 nm/s², especially during the winter (Watlet et al., 2020). This should be considered when performing e.g. tidal analyses.