Department of Applied Mathematics, Northwestern Polytechnical University,Shaanxi 710129, P.R.China;
Department of Applied Mathematics, Northwestern Polytechnical University,Shaanxi 710129, P.R.China;
State Key Laboratory of Remote Sensing Science, Chinese Academy of Science,Beijing 100101, P.R.China;
Department of Mathematics and information, Qinghai Normal University,Qinghai 810008, P.R.China;