In case of satellite-based measurement techniques, e.g., GNSS, the height component is relative to a geocentric reference ellipsoid, which is a mathematical idealized representation of the physical Earth.

In theory, the geoid coincides with the surface of a homogeneous ocean effected only by gravitation and Earth rotation, i.e., under the absence of external forces such as winds, tides, etc. Heights are typically measured as vertical distances to the geoid as zero-level elevation surface. The new gravity data changed the geoid model heights by up to 15 cm in areas of sparse/non-existing gravity data. When the GNSS derived geoid heights are compared with geoid heights from the geoid models differences between the respective models are seen in the most eastern and southern parts of the campaign area. From the GNSS and sea surface data we were able to obtain geoid heights at sea areas with an accuracy of a few centimetres. The campaign was carried out with the marine geology research catamaran Geomari (operated by the Geological Survey of Finland), which sailed back and forth the eastern part of the Finnish territorial waters of the Gulf of Finland during the early summer of 2018. Additionally, a new geoid model, calculated using the newly collected marine gravity data, was validated. In this research, we present a marine GNSS/gravity campaign where existing geoid models were validated at sea areas by GNSS measurements in combination with sea surface models. As such benchmarks cannot be established offshore, marine areas of geoid models must be evaluated in a different way. Traditionally, geoid models have been validated using GNSS-levelling benchmarks on land only.

Manual geoid model reader