1. School of Marine Science and Technology, Northwestern Polytechnical University, 26487 Xi'an, Shaanxi, China, 710072 (e-mail: taoxiuye@mail.nwpu.edu.cn)
2. Northwestern Polytechnical University, 26487 Xi'an, Shaanxi, China, 710072 (e-mail: ning1010@mail.nwpu.edu.cn)
3. Automation, Northwestern Polytechnical University, Xi'an, China, 710072 (e-mail: lihuiping@nwpu.edu.cn)
4. Northwestern Polytechnical University, 26487 Xi'an, Shaanxi, China, 710072 (e-mail: xudm@nwpu.edu.cn)