Study of a vertical gravity gradient at the MUT area

Abstract

Any object on the globe, in addition to the gravitational force, is affected by the force associated with the rotation of the Earth, i.e., the centrifugal force, which together define the force of gravity. Due to various factors, both external (the influence of other celestial bodies) and internal (the inhomogeneous internal structure of the Earth), the gravity depends on the location and time of observation. The study on gravity is made possible by using extremely sensitive measuring devices called gravimeters, which are a branch of physical geodesy called geodetic gravimetry. Geodetic gravimetry is widely used in geodesy to study the shape of the geoid and the realisation of gravimetric control networks or in geophysics to detect mineral deposits, underground watercourses or caves. However, in order to obtain reliable results, it is necessary not only to measure the gravity accurately, but also to reduce these measurements adequately. This is possible by determining, among other things, the vertical gravity gradients (VGG), which are used to reduce the measured gravity values to any reference level. In our research, we focused on analysing the change in the value of VGGs in the closed area of the Military University of Technology (MUT). We used 33 points of the existing vertical and horizontal networks of the MUT for measurements. We performed the observations using ZLS Burris model B-67 spring gravimeter at several heights in the range of 0.1 m to 1.3 m using a specially constructed tripod. We showed that the values of the vertical gradients vary over the selected area from ‒0.2534 mGal/m to ‒0.3917 mGal/m. The obtained results show consistency with the spatial distribution of changes of the topography of the terrain, the density of the Earth’s crust, and the type of geological formations present beneath the surface. In the study, we also showed the relevance of using the actual (measured) values of gradients to analyse geoid-to-quasigeoid separation. We have shown that taking the actual gradient values instead of their average (or modelled) values results in deviations in modelling the separation of both geodetic reference surfaces of up to 2 mm in the study area.Keywords: gravity, vertical gravity gradient, gravimetry, geoid-quasigeoid separation