velocity products from pulse pair

The first product (Level_2a_UGD) is the geophysical velocity U_GD that is obtained by subtracting the non-geophysical Doppler from the line of sight velocity and projecting on the Earth surface.

U_GD is expected to contain a large wave bias U_WB that is related to the surface Stokes drift vector U_S . and a near-surface current in the radial direction U_R .  For Ka-band at 6 and 12° incidence, the magnitude of U_WB generally matches the theory by Nouguier et al. (2018), with U_WB of the order of 25 times the radial component of the Stokes drift.