This paper proposes a method with which mobile robots can explore unknown environments efficiently and effectively. For mobile robots, developing exploration methods in unknown environments is a challenging target. Navigation for environment monitoring is necessary in order to explore
efficiently in unknown environment. Although a frontier-based exploration can be seen as a conventional method, this method is not necessarily a global optimal planning method, because it explores for the local optimal in each situation; in the monitoring task, it could fall into the local
solution, because it could not take into consideration the overall observation efficiency. The proposed method exploits the whole observation and knowledge about the area of the unknown environment. It is possible for the proposed method to establish a global plan in consideration of efficiency
and effectiveness by integrating pattern and frontier-based exploration. In simulation, it is shown that the proposed method of pattern and frontier-based exploration is useful for exploring unknown environments efficiently and effectively.