# A New Model of Quasigeoid for the Baltic Sea Area
## Data
### Global Geopotential Models  
A global geopotential model is necessary to calculate N\({}_{\text{GM}}\) Equation (6) and \(\Delta\)g\({}_{\text{GM}}\) Equation (8) in geoid/quasigeoid modeling. The first global model describing the gravity field was developed by [PERSON] in 1956. Since then, significant progress has been made in computing global geopotential models.  
Initially, geopotential models were counted from observations of satellite perturbations, followed by the combined development of satellite perturbations and terrestrial and ocean gravity anomalies. The land anomalies are contaminated by systematic errors due to various regional vertical reference systems [37]. Since biased heights enter into the computation of terrestrial gravity anomalies, which in turn are used for geoid determination, the biases enter as a secondary or indirect effect also in such a geoid model. In contrast to terrestrial gravity anomalies, gravity and geoid models derived from satellite  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Data** & **n** & **Mean** & **Std dev** & **Min** & **Max** \\ \hline Combined & & & & & \\ data set & 150,842 & \(-7.0\) & 16.7 & \(-102.6\) & 212.5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Statistics of the gravity data used in this study (in mGal).  
Figure 3: SRTM30 topography model in meters for the area of the Baltic sea and surrounding lands.  
gravity missions, and in particular from GRACE and GOCE, do not suffer from those inconsistencies. Those models can be regarded as unbiased [38].  
In this work, three geopotential satellite models were used, namely GOCO06s order and degree 300 [39], GOCE-DIR6 order and degree 300 [40], and combination model EIGEN-6C4 order and degree 2190 [41].  
GOCO06s (2019) is the latest satellite-only global gravity field model computed by the GOCO (Gravity Observation Combination) project. It is based on over a billion observations acquired over 15 years from 19 satellites with different complementary observation principles. This combination of different measurement techniques is key in providing consistently high accuracy and the best possible [42] spatial resolution of the Earth's gravity field  
GOCE-DIR6 (2019) is a result of the gravity field. and steady-state Ocean Circulation Explorer (GOCE) gravity gradient data of the entire science mission and data from LA-GEOS 1/2 and Gravity Recovery and Climate Experiment (GRACE) were combined in the construction of a satellite-only gravity field model to a maximum degree of 300. When compared to Earth Gravitational Model 2008, it is more accurate at low to medium resolution, thanks to GOCE and GRACE data. When compared to earlier releases of European Space Agency GOCE models, it is more accurate at high degrees owing to the larger amount of data ingested, which was moreover taken at a lower altitude.  
EIGEN-6C4 (2014) is a static global combined gravity field model up to degree and order 2190. It has been elaborated jointly by GFZ Potsdam and GRGS Toulouse. The combination of the different satellite and surface data sets has been done by a band-limited combination of normal equations (to max degree 370), which are generated from observation equations for the spherical harmonic coefficients. A brief description of the applied techniques for the generation of such a combined gravity field model is given in [43]. The resulting solution to degree/order 370 has been extended to degree/order 2190 by a block diagonal solution using the DTU10 global gravity anomaly data grid.