@article{tang2012nonnegative,
  title={Nonnegative matrix factorization for hyperspectral unmixing using prior knowledge of spectral signatures},
  author={Tang, Wei and Shi, Zhenwei and An, Zhenyu},
  journal={Optical Engineering},
  volume={51},
  number={8},
  pages={087001--087001},
  year={2012},
  publisher={Society of Photo-Optical Instrumentation Engineers}
}