To cite package 'smoothie' in publications use:

Gilleland, E. (2013) Two-dimensional kernel smoothing: Using the R package smoothie. NCAR Technical Note, TN-502+STR, 17pp. Available at: http://opensky.library.ucar.edu/collections/TECH-NOTE-000-000-000-869

Corresponding BibTeX entry:

  @TechReport{,
    title = {Two-dimensional kernel smoothing: Using the R package
      smoothie},
    author = {Eric Gilleland},
    institution = {NCAR Technical Note, TN-502+STR, 17pp.},
    year = {2013},
    url =
      {http://opensky.library.ucar.edu/collections/TECH-NOTE-000-000-000-869},
  }