To cite landsat in publications use:

Goslee, Sarah C. (2011). Analyzing Remote Sensing Data in R: The landsat Package. Journal of Statistical Software, 43(4), 1-25.<doi:10.18637/jss.v043.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},
    doi = {10.18637/jss.v043.i04},
  }