The OCTAS poject, The geoid, the mean sea surface and the mean dynamic topography

The OCTAS project, Ocean Circulation and Transport Between North Atlantic and the Arctic Sea, funded by the Norwegian Research Council, is a multidisciplinary project combining geodesy, satellite altimetry and oceanography. The main objective is to enhance the Norwegian capacity in Earth observation technologies through determining the ocean circulation and transport by using satellite techniques in combination with geodesy. The primary study area is the Fram Strait between Svalbard and Greenland. A vital objective is the determination of a high precision gravimetric geoid for the OCTAS study area. This requires an error free high quality gravimetric dataset. The process of establishing such a data set by adjusting older marine data through comparison with modern airborne and marine gravity data sets is described. Combining this updated gravity data set with data from the CHAMP and GRACE satellites an OCTAS geoid has been computed. The updated gravity field and the derived geoid may be used in validating the GOCE products. The challenges and efforts undertaken in deriving a high precision mean sea surface in a region with an abundance of sea ice and limited number of altimetric satellites is described. The derived geoid and mean sea surface is combined to form the mean dynamic topography, MDT. These MDT’s are assessed by intercomparing with oceanographically derived MDT models. The status and an overview of the project is given including identification of challenges that must be addressed in order to achieve the project objectives.