Review of ground and aerial methods for vegetation cover fraction (fCover) and related quantities estimation: definitions, advances, challenges, and future perspectives - Linyuan Li; Xihan Mu; Hailan Jiang; Francesco Chianucci; Ronghai Hu; Wanjuan Song; Jianbo Qi; Shouyang Liu; Jiaxin Zhou; Ling Chen; Huaguo Huang; Guangjian Yan (ISPRS Journal of Photogrammetry and Remote Sensing, 2023)