Xuefeng, Liu, et al. “Estimation of Carbon and Nitrogen Contents in Citrus Canopy by Low-Altitude Remote Sensing”. International Journal of Agricultural and Biological Engineering, vol. 9, no. 5, Sept. 2016, pp. 149-57, https://ijabe.migration.pkpps03.publicknowledgeproject.org/index.php/ijabe/article/view/2246.