A qualitative assessment of desertification change in the Tarfaya basin (Morocco) using panchromatic data of Landsat ETM+ and oli: sand encroachment approachAli Aydda, Ahmed Algouti and Abdellah AlgoutiMATEC Web Conf., 120 (2017) 09002DOI: https://doi.org/10.1051/matecconf/201712009002