To cite the spsurvey package in publications use:

Kincaid, T. M. and Olsen, A. R. (2013). spsurvey: Spatial Survey Design and Analysis. R package version 2.6. URL: http://www.epa.gov/nheerl/arm/.

Corresponding BibTeX entry:

  @Manual{,
    title = {spsurvey: Spatial Survey Design and Analysis},
    author = {Thomas M. Kincaid and Anthony R. Olsen},
    year = {2013},
    note = {R package version 2.6},
    url = {http://www.epa.gov/nheerl/arm/},
  }