1. Faculty of Science and Technology, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, 1432 Ås, Norway
2. Geodetic Institute, Norwegian Mapping Authority, Kartverksveien 21, 3511 Hønefoss, Norway
3. Geodesy and Glaciology, Bavarian Academy of Sciences and Humanities, Alfons-Goppel-Str. 11, 80539 Munich, Germany