@misc{1157996,
  author = {Kenneth P Spies},
  title = {Mode calculations for VLF propagation in the earth-ionosphere waveguide:},
  year = {1961},
  month = {1961-01-01 05:01:00},
  publisher = {, National Institute of Standards and Technology, Gaithersburg, MD},
  doi = {https://doi.org/10.6028/NBS.TN.114},
  language = {en},
}