Gravimetry is the scientific discipline, which deals with instruments ('gravimeters') and procedures to measure the strength of a gravity field. It also includes the processing, analysis, and interpretation of gravity measurements. The latter are used to determine the gravity field of the Earth, to measure the gravity signal of earthquakes e.g. as part of an earthquake or tsunami early warning systems, to monitor oil and gas fields, to measure absolute vertical deformations of the Earth's crust or to identify fracture zones in the subsurface. Absolute gravimeters measure the strength of the gravity field, relative gravimeters measure the difference of the strength at two stations or time-variations of the strength at a single station. The Physical and Space Geodesy group of the Department of Geoscience and Remote Sensing operates several relative gravimeters from Scintrex and LaCoste Romberg, the LaCoste Romberg tidal gravimeter ET-15, which has been designed specifically to measure earth tides, and a FG-5 absolute gravimeter.
Scintrex CG-3M relative gravimeter (left), the gravity bunker at the Westerbork Astrometric-Geodetic Observatory (middle) and the TU Delft FG-5 absolute gravimeter (right)
The research on gravimetry focuses on i) the study of environmental processes such as atmospheric mass variations, tides, ocean loading, groundwater level variations, and soil moisture variations on gravity, and ii) the use of absolute gravity observations to control the absolute vertical motion on Normaal Amsterdams Peil (NAP), the reference of the Netherlands height system.