Gravity above massive rectangular piers: measurements, reduction and modelling

We performed a 3D microgravity survey of three indoor concrete piers with relative gravimeters. The threeScintrex CG-5 were used for this task. The measurements were performed according to a pre-planned schedule onfour height levels over nine points above piers, which also were connected with each other over benchmarks. Inall, more than 250 ties were carried out about a month. The measurements were adjusted with a robust algorithm.The geocentric coordinates of the corners of the piers have also been measured for reductions. We comparedthe unreduced and reduced adjusted results with a simple gravitational attraction of a rectangular prism. We alsoanalyzed the uncertainty caused by displacement from a benchmark of the absolute and, more importantly, relativegravimeters on massive pillars. The main result, however, is a high-precision 3D empirical model of the threeconnected piers, which can be used to transfer gravity value to any instrument with any reasonable referenceheight and any reasonable displacement from a benchmark.