R. Forsberg, K. Keller, C. S. Nielsen, N. Gundestrup, C. C. Tscherning, S. N. Madsen3, J. Dall: Elevation change measurements of the Greenland Ice Sheet (PDF) (2. GPS measurement at GRIP pole. Fig. 3. Ice movements around NGRIP, relative to the deep central pole.) Earth Planets Space, 52, 1049–1053. 2000. (englanniksi)