The authors have researched into a novel localization system for an unmanned aerial vehicle (UAV) for automatic structure visual inspection. In environment around large scale facilities such as under a bridge, automatic flight does not work due to the GNSS signals not reaching the UAV. This paper proposes a localization system using subsidiary UAVs (sub-UAVs) that assist localization of an UAV (main-UAV) working in the vicinity of facilities. Sub-UAVs acquires its own position information by GNSS and relative position information by vision sensor. Main-UAV localizes its own position by integrating the information obtained from measurements of all Sub-UAVs. In this paper, we model two types of measurement, GNSS and vision sensor, by Sub-UAVs to realize the proposed system. Then, the parameters associated with modeling are confirmed through basic experiments, and the effectiveness of the system is confirmed by simulation.
