Department of Information and Communication;
University of Electronic Science and Technology of China;
Chengdu 610051;
China;
Department of Electrical and Information Engineering;
Heilongjiang Institute of Engineering;
Harbin 150026;
China;
College of Economics and Management;
University of Chinese Academy of Sciences;
Beijing 100049;
China;
small target; track-before-detect(TBD); nonstationary sea clutter; closely spaced target;