Changes in Water Surface Area of the Lake in the Steppe Region of Mongolia: A Case Study of Ugii Nuur Lake, Central Mongolia oleh Erdenesukh Sumiya, Batsuren Dorjsuren, Denghua Yan, Sandelger Dorligjav, Hao Wang, Altanbold Enkhbold, Baisha Weng, Tianlin Qin, Kun Wang, Tuvshin Gerelmaa, Oyunbaatar Dambaravjaa, Wuxia Bi, Yuheng Yang, Byambabayar Ganbold, Mohammed Gedefaw, Asaminew Abiyu, Abel Girma