Velocity correction

The radial velocity is corrected for platform motion using two different methods. The first corrects for platform motion using INS/GPS measurements (VelRaw->Vel). It is applied to all of the data and results in a significantly improved data set. 


An additional correction is applied to the nadir-looking data only: The radial velocity of the surface, which is assumed to be 0 m/s, is used as a reference to correct the data (Vel->VelCorr) following Ellis et al. (2017). The velocity of the ocean surface, which is rather noisy because of the strong wave activity in the Southern Ocean, is filtered by first applying a 3 point running mean and then fitting a 3rd order polynomial over a running 20 second interval.


The second step further improves the overall quality and gets rid of remaining biases.