Output Feedback Stabilization of Inertial Stabilized Platform with Unmatched Disturbances Using Sliding Mode Approach * *This paper was supported by the foundation of International Science & Technology Cooperation Program of China (2015DFA10490), the National Natural Science Foundation of China (61473080), and the Fundamental Research Funds for the Central Universities and the Innovate Foundation for Graduate Student of JiangSu Province (KYLX15-0213).