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 DFG large-scale equipment transportable superconducting gravimeter iGrav #043

The German Research Foundation (DFG) and the state of Northrhine-Westphalia had agreed to fund the acquisition of a transportable superconducting gravimeter iGrav, manufactured by GWR Instruments. 

GWR delivered the iGrav #043 in December 2019 first to the Walferdange Underground Laboratory for Geodynamics (WULG) for calibration purposes, and measurements could commence in January 2020.
At WULG, the calibration factor of the new iGrav was determined using simultaneously collected measurements from the calibrated Observatory superconducting gravimeter OSG-CT040 that operates continuously since 2002. It was found that an initially fast exponential drift became almost perfectly linear about 1.5 months after installation. More details are found in Elsaka et al., (2022).

The iGrav #043 was then brought to the University of Bonn Todenfeld Observatory, about 30 km south of Bonn, in January 2023. Since that time, the iGrav-043 measures variations of gravity continuously.



Figure 1: The iGrav #043 at the Todenfeld Observatory with its main components; Dewar and Compressor.

The system, gravimeter and compressor, consumes 1.3 KW at 220 VAC, 50/60 Hz. The dewar has a height of 102 cm and a diameter of 36 cm with a weight of 30 kg. The iGrav is equipped with an enclosure system that allows deployment in field conditions.

A superconducting gravimeter measures the time variations of the gravity force due to Earth and ocean tides, the Earth’s ongoing deformations including atmospheric and ocean loading, and surface and subsurface water mass changes; these effects can be even smaller than one Billionth of gravity (9,81 m/s²). The sensor is a 2.5 cm wide and 5 grams light sphere made of Niobium. Cooled to superconducting state, the sphere, the sensing unit, can steadily levitate in vacuum, through an external, nest-shaped magnetic field without any significant losses. It changes its relative position only due to variations of the gravity force or when the ground itself moves. To maintain the superconducting state, the iGrav sensor is operated at 4.2 K inside a dewar filled with liquid helium and integrated with a 4 K refrigeration system.

The iGrav can be used for geodetic, geophysical and hydrological applications that require higher stability and precision than provided by mechanical spring-type gravity meters, e.g. serve as high-precision continuous gravity reference station for studying geophysical phenomena with a range in periods from one second to several years, monitoring volcanoes, measurement of ocean-loading corrections to gravity for improving global ocean tide models, hydrological, geothermal, and non-invasive ground water monitoring, measurement of subsidence caused by oil, gas, or water extraction, long term tectonic effects-either post-glacial uplift or subsidence, subduction-induced silent earthquakes, aquifer monitoring and management; measuring depletion and recharging of municipal water supplies, gravity measurements around active faults, volcanic systems, and regions of active subsidence for the understanding of their scientific processes and societal hazards.

 Contact: Dr. Basem Elsaka ([Email protection active, please enable JavaScript.])