Since 1995 sea level measurements have been carried out with a pressure sonde. But occasional changes in the reference height caused by the need to install new equipment or by collisions with drift ice permit only limited assertions about long-term sea level change. In addition, using high-precision levelling to relate heights to the reference points of measurement systems based on a space-geodetic technique is complex and time-consuming. For this reason, in February 2011 a GNSS-referenced radar sonde was installed, which can, however, only be operated during Antarctic summertime. Nevertheless, the pressure sonde data can be calibrated with the help of data for individual measurement periods and combined to produce a height-referenced series. This makes it possible to distinguish sea level variations from crustal movement.
When these data are combined with the results from the GNSS stations OHI2 and OHI3 and the VLBI antenna, the ellipsoidal height of the sea level mean can be determined. Depending on the data source, it varies from 21,251 to 21,266 meters above the surface of the WGS 84 reference ellipsoid and is equivalent to the height of the geoid plus the mean dynamic topography of the ocean surface.
Ellipsoidal height of the sea level mean, determined by combining gauge measurements, GNSS and VLBI results, and high-precision levelling. Source: Klügel, Höppner et al. (2014): Polar Record, doi:10.1017/S0032247414000540.