@misc{indiciae9019ab620236,
  title = {Multispectral techniques for general geological surveys - evaluation of a four-band photographic system},
  author = {D. F. Crowder},
  year = {1969},
  doi = {10.3133/ofr6964},
  url = {https://pubs.usgs.gov/publication/ofr6964},
  note = {Source identifier: ofr6964}
}