To cite npphen in publications use:

Chávez, R.O., Estay, S.A., Riquelme, C.G. (2017). npphen. An R package for estimating annual phenological cycle. Uach, PUCV, Chile.

Corresponding BibTeX entry:

  @Manual{,
    title = {{npphen}: An R package for estimating annual phenological
      cycle},
    author = {Roberto O. Chávez and Sergio A. Estay and Carlos G.
      Riquelme},
    year = {2017},
  }