The first product (Level_2a_UGD) is the geophysical velocity UGD that is obtained by subtracting the non-geophysical Doppler from the line of sight velocity and projecting on the Earth surface.
UGD is expected to contain a large wave bias UWB that is related to the surface Stokes drift vector US . and a near-surface current in the radial direction UR . For Ka-band at 6 and 12° incidence, the magnitude of UWB generally matches the theory by Nouguier et al. (2018), with UWB of the order of 25 times the radial component of the Stokes drift.