@unpublished{FreedenMichel2000,
  author  = {Willi Freeden and Volker Michel},
  title   = {Basic Aspects of Geopotential Field Approximation From Satellite-to-Satellite Tracking Data},
  institution = {Fachbereich Mathematik},
  series    = {Berichte der Arbeitsgruppe Technomathematik (AGTM Report)},
  number    = {232},
  year    = {2000},
  url  = {http://nbn-resolving.de/urn:nbn:de:hbz:386-kluedo-10539},
}