Comparison of Different Approaches to Gravity Determination and Their Utilization for Calculation of Geopotential Numbers in the Slovak National Levelling Network

摘要

Vertical reference system in the Slovak Republic is realized by the first and second order of the National levelling network with the normal heights according to Molodenski. The reference heights are still calculated by the traditional method using the components of gravity correction. Nowadays we are preparing a new realization of the height system which will be based on geopotential numbers. But there is a problem with the absence of the measured gravity values. Only at approximately 8% of levelling points we have the measured values of gravity. Therefore, we are trying to find the most reliable method for estimation of the gravity values and use them subsequently for determination of the geopotential numbers. The aim of this study is to analyze the different ways to the gravity determination and their application for calculation of the geopotential numbers on the points of the National levelling network. The first method is based on the reconstruction of the gravity on levelling points from the interpolated values of the complete Bouguer anomaly using the proprietary software. The second method is based on the modern global geopotential models improved by the residual terrain model approach. Calculated gravity was compared with directly measured gravity. The set of the points contained all geodetic control points within Slovakia where the gravity has been measured. Then, the calculated value of gravity was used to determine the geopotential numbers and normal heights according to Molodenski in the first order levelling lines of the National levelling network which connect the reference points determined within EVRF2007 adjustment for area of Slovakia.