If the ocean surface were unaffected by hydrodynamic processes, it would be in equilibrium with gravity and perpendicular to the local plumb line. It would therefore coincide with an equipotential layer of the Earth and represent the geoid. However, winds and currents cause the sea surface to deviate from the geoid by up to two meters. This deviation is called Dynamic Ocean Topography (DOT).

Knowledge of the DOT can be used to calculate the velocity of geostrophic ocean surface currents. This information, in turn, is useful to estimate oceanic mass and heat transport. The resolution and accuracy of DOT has greatly improved over the last decade thanks to the availability of long time series of sea surface heights (SSH) from satellite altimetry in combination with precise marine gravity field data from dedicated gravity field missions such as GOCE.

DGFI-TUM has developed an approach to determine DOT directly along individual ground tracks of the altimeter satellites (profile approach), applying identical filters to SSH and geoid data. The result of this approach are instantaneous (i.e., time-varying) DOT values (called iDOT) along the track. In areas of low data coverage, e.g., due to sea ice, the altimetry data can be combined with information from ocean models to fill data gaps and improve the resolution. DGFI-TUM is working on special preprocessing methods for the computation of iDOT, as well as approaches for spatial interpolation and combination with ocean models. In addition, validation and interpretation of the derived datasets is performed.