@unpublished{FreedenMichel1999,
  author  = {Willi Freeden and Volker Michel},
  title   = {Least-squares Geopotential Approximation by Windowed Fourier and Wavelet Transform},
  institution = {Fachbereich Mathematik},
  series    = {Berichte der Arbeitsgruppe Technomathematik (AGTM Report)},
  number    = {216},
  year    = {1999},
  url  = {http://nbn-resolving.de/urn:nbn:de:hbz:386-kluedo-8075},
}