@misc{indiciae7081dcd38581,
  title = {Spectral characteristics of geomagnetic field variations at low and equatorial latitudes},
  author = {W.H. Campbell},
  year = {1977},
  doi = {10.1016/0021-9169(77)90031-9},
  url = {https://pubs.usgs.gov/publication/70010407},
  note = {Source identifier: 70010407}
}