1. School of Computer Science and Technology, Xi'an Jiaotong University, Xi'an Shaanxi, China
2. School of Electronic Information and Electrical Engineering, Shanghai Jiao Tong Univesity, Shanghai, China
3. School of Oceanography, Shanghai Jiao Tong University, Shanghai, China
4. State Key Laboratory of Resources and Environmental Information System, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China