INTERNATIONAL HYDROGRAPHIC REVIEW 
MAY 2020 
71 
After a feasibility study, it was decided and agreed that the harmonized vertical datum will be 
based on the European Vertical Reference System (EVRS). In September 2013, the 18 th Baltic 
Sea Hydrographic Commission Conference decided to continue the work of the Chart Datum 
Working Group (CDWG) and wished the harmonized Baltic Sea vertical reference to be 
implemented. IHO BSHC has approved the name and the adoption of the Baltic Sea Chart Datum 
2000 and the abbreviation BSCD2000. 
BSCD2000 has been registered as Chart Datum number 44 in the IHO Geospatial Information 
(Gl) Registry and can therefore be used as a reference datum in all future S-100 1 products. It 
applies to all national realizations of the European Vertical Reference System (EVRS). 
The basic prerequisite for the realization and introduction of the BSCD2000 is the determination 
of a model of the height reference surface with sufficient accuracy. The practical works were 
significantly supported by the FAMOS project (www.famosproject.eu) which was co-financed by 
the European Commission. FAMOS stands for “Finalizing Surveys for the Baltic Motorways of the 
Sea” and is part of the “Motorways of the Seas”, a concept to develop European maritime traffic 
infrastructure within the framework of the Trans-European Transport Network (TEN-T) policy. 
Major activities within FAMOS consisted of the coordination and execution of shipborne 
campaigns to measure the gravity data needed to compute an improved geoid model as the HRS 
for the BSCD2000, as well as the computations of the geoid 2 model itself. 
3. Definition and realization of BSCD2000 
In the following, only a general overview shall be given from the user’s perspective. For the full 
geodetic detail, the reader is referred to the BSCD2000 paper (Agren et al., 2019). 
The first of the two most important characteristics of BSCD2000 is that it is not anymore 
defined with respect to the (changing) local mean sea level (MSL). 
Instead, a well-defined uniform and accessible height reference surface (HRS) is used that is 
equal to the distinct equipotential surface of the Earth’s gravity field called the geoid. 
The instantaneous sea surface is deflected from the above equilibrium surface due to ocean 
dynamics (induced by currents, temperature, salinity variations, wind etc.) in combination with the 
coastal shape and bathymetry. The long-term average of these deflections is not zero, hence the 
mean sea surface is offset from the geoid. The static part of this difference, which can reach up to 
approximately ±2 m worldwide, is called mean dynamic topography (MDT). It can be observed 
and computed either from oceanographic models or from combined space-geodetic observations 
(altimetry and gravity satellite missions). In the Baltic Sea, the MDT is generally positive 
(compared to the MSL/MDT of the North Sea) with a slope of approx. 30 cm towards the North 
east, corresponding mainly to decreasing salinity. Figures 4 and 5 show examples for a geoid 
model and a space-geodetic MDT model of the Baltic Sea, respectively. 
1 
- The S-100 Standard (https://iho.int/en/s-100-universal-hvdroaraphic-data-model. last access May 15, 2020) is a 
framework document that is intended for the development of digital products and services for hydrographic, maritime 
and GIS communities. It comprises multiple parts that are based on the geospatial standards developed by the 
International Organization for Standardization (IHO). 
2 
- The geoid describes the undisturbed sea level in equilibrium as if there were no external forces (wind, currents, tem 
perature, salinity). In geodesy, it is the classic height reference surface for the realization of “heights above sea level’’ 
on land.