To cite landsat in publications use:

Sarah C. Goslee (2011). Analyzing Remote Sensing Data in R: The landsat Package. Journal of Statistical Software, 43(4), 1-25. URL http://www.jstatsoft.org/v43/i04/.

Corresponding BibTeX entry:

  @Article{,
    title = {Analyzing Remote Sensing Data in {R}: The {landsat}
      Package},
    author = {Sarah C. Goslee},
    journal = {Journal of Statistical Software},
    year = {2011},
    volume = {43},
    number = {4},
    pages = {1--25},
    url = {http://www.jstatsoft.org/v43/i04/},
  }