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ESTIMATION OF NORMAL AND GEOPOTENTIAL HEIGHT DIFFERENCES DERIVED BY GRAVITY DATA FROM GLOBAL GEOPOTENTIAL MODELS FOR THE TERRITORY OF BULGARIA

Tatyana Lambeva

Abstract

The paper analyzes normal corrections for the determination of the normal height differences along the First Order Levelling lines in Bulgaria. Normal corrections are calculated in two ways – with measured gravity accelerations and with gravity data from Global Geopotential Models (GGM). The study uses the last contemporary GGMs developed up to 2160-2190 degree and ultra-high resolution GGMPlus model. Calculations for Bouguer anomalies are made by the calculation service in the International Centre for Global Earth Models (ICGEM). The method for determination of the interpolated values of the gravity anomalies is based on that considered in [15] for all GGMs, with the exception of the interpolated data from GGMPlus. Gravity anomalies from GGMPlus are calculated by using known and modelled data for the height anomalies. In particular, the paper studies the accumulation of systematic errors along the levelling line due to modelled gravity data. Systematic and random error in the differences between the modelled and measured normal corrections are calculated by the Lallemand’s formulas. Although the main part of the value of the gravity anomaly is formed by the development up to degree 2160, the contribution of the omission part of the development can have a significant impact in the conditions of anomalous gravitational fields and in mountain areas. Calculated systematic and random errors are negligible in a smooth gravity field. Application of the present GGM data for each separate levelling distance is possible only for flat areas with a weak anomaly field. The determination of geopotential numbers and geopotential differences can be performed in two ways leading to identical results. The first is the classic one – by using the reduced gravity acceleration values and measured levelling differences. The second one is direct – by using the direct relationship between geopotential differences and normal height differences.

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DOI resolver: doi.org/10.5593/sgem2021/2.1/s09.45

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