Fig. 4

Relative standard deviation of equivalent water height residuals over 4 years (2003–2006) derived from simulated true and noisy GRACE gravity field solutions using the DDK filter only and by applying the DDK filter and the global grid point gain factors: \(\text {true} - \text {DDK filter}\) (left), \(\text {true} - (\text {DDK filter},k^\text{org})\) (middle) and \(\text {true} - (\text {DDK filter},k)\) (right)