Role of Near Topography and Building Effects in Vertical Gravity Gradients Approximation

Importance of precise vertical gradient of gravity (VGG) determination by means of relative gravity measurements is mainly connected with absolute gravity measurements and setting of global and local gravity reference networks. The gravitational effect of the topography and near building structures and their contribution on the vertical gradient of gravity (VGG) was studied. A strong impact of near topography on the VGG values was found in the case of the mountainous areas - deviations up to 88 percent of normal value were obtained by means of relative gravity measurements. Near building structures gravitational effect was estimated by means of simple polyhedrons - very specific nonlinear behaviour of VGG is demonstrated on two model examples. Synthetic tests for the estimation of determined VGG precision are also presented. The error of polynomial estimation of the VGG can be several times higher than the error within measured gravity. For a set of 29 real measurement points a relatively good coincidence between the measured and calculated VGG values was achieved. Application of predicted values of the VGG instead of the normal ones in cases of unknown actual values can lead to a quality improvement of gravimetric reference networks, as well as prospecting VGG measurements.