@article{168568,
      url = {http://digitallibrary.un.org/record/168568},
      title = {Survey of observation structures.},
      publisher = {United Nations Sudano-Sahelian Office,},
      recid = {168568},
      pages = {vi, 126 p. :},
      address = {New York :. 1991},
      year = {1991},
}