The Mean Dynamic Topography is the permanent stationary component of the ocean dynamic topography.
This mean circulation is not an immediate product of altimetry data. Those data give more the mean sea surface, which contains the marine geoid plus the sea elevation due to the mean oceanic. So we have to combine altimetric data with others (in-situ, gravimetric satellites…), to precisely determine the geoid, and by subtracting it, compute the mean circulation.

fig 1. GOCE User Toolbox Workflow (Credits DTU)

 

The MDT computation can be performed with the GOCE User Toolbox [Bingham et al 2015]

fig 2. Mean dynamic topography, i.e. oceanic relief corresponding to permanent ocean circulation. Arrows are proportional to current speed. (Credits CNES/CLS)