To cite ramps in publications use:

Smith BJ, Yan J, Cowles MK (2008). “Unified Geostatistical Modeling for Data Fusion and Spatial Heteroskedasticity with R Package ramps.” Journal of Statistical Software, 25(10), 1-21.

Corresponding BibTeX entry:

  @Article{,
    title = {Unified Geostatistical Modeling for Data Fusion and
      Spatial Heteroskedasticity with R Package ramps},
    author = {Brian J. Smith and Jun Yan and Mary Kathryn Cowles},
    year = {2008},
    journal = {Journal of Statistical Software},
    volume = {25(10)},
    pages = {1-21},
  }