@unpublished{BerkelMichel2008,
  author  = {Paula Berkel and Volker Michel},
  title   = {On Mathematical Aspects of a Combined Inversion of Gravity and Normal Mode Variations by a Spline Method},
  institution = {Fachbereich Mathematik},
  series    = {Schriften zur Funktionalanalysis und Geomathematik},
  number    = {41},
  year    = {2008},
  url  = {http://nbn-resolving.de/urn:nbn:de:hbz:386-kluedo-15800},
}