1. http://op.gfz-potsdam.de/grace/index_GRACE.html
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3. http://op.gfz-potsdam.de/champ/index_CHAMP.html
4. http://www.dfd.dlr.de/archive/dims/dims_www_paper.html
5. DIMS Technical Summary, DIMS-DLR-GEN-CS-0004, Issue 1.1, October 1997.