To cite ramps in publications use:

Smith B, Yan J, Cowles M (2008). “Unified geostatistical modeling for data fusion and spatial heteroskedasticity with R package ramps.” Journal of Statistical Software, 25(10), 1–21. doi:10.18637/jss.v025.i10, https://www.jstatsoft.org/v25/i10.

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},
    number = {10},
    pages = {1--21},
    doi = {10.18637/jss.v025.i10},
    url = {https://www.jstatsoft.org/v25/i10},
  }