1. School of Surveying and Land Information Engineering, Henan Polytechnic University, Jiaozuo
2. Key Laboratory of Soil and Water Conservation on the Loess Plateau of Ministry of Water Resources, Yellow River Institute of Hydraulic Research, Yellow River Conservancy Commission, Zhengzhou, People’s Republic of China
3. Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, People’s Republic of China
4. Department of Ecology and Conservation Biology, Texas A&M University, College Station, USA