AgriEngineering AgriEngineering UAV detection of Sinapis arvensis infestation in alfalfa plots using simple vegetation indices from conventional digital cameras Sánchez-Sastre Luis Fernando Casterad M. Auxiliadora Guillén Mónica Ruiz-Potosme Norlan Miguel Alte da Veiga Nuno M.S. Navas-Gracia Luis Manuel Martín-Ramos Pablo Universidad de Zaragoza 2020 research-article