In many spatial regions other than the ocean, technology for predicting phenomena from information acquired in real-time has been established. Also, in the open ocean, sub-real-time measurement and construction of ocean models are being promoted by the observation system such as Argo float. However, especially in coastal areas and sea ice areas, many observations have been performed using a vessel, and it is a bottleneck for a real-time observation. For the next-generation observation that requires a large amount of information in real-time, the application of unmanned aerial vehicle (UAV) to ocean observations offers important possibilities. UAVs also excel in terms of manufacturing costs, operating costs, and mobility. In this study, a UAV for underwater observation was developed by equipping expendable conductivity temperature depth profiler (XCTD) and expendable bathythermograph (XBT) observation devices. We also conducted verification experiments in the actual sea area. Experiment result and obtained data suggest that the UAV developed in this study is suitable for this observation and could propose an effective new use case. It is particularly suitable for periodic observations at fixed point, multi-point observation, and limited confirmation work that does not require using a vessel. However, capabilities of drone-like UAV (used in this study) for flight distance and payload do not satisfy all observation maneuvers. In the future, to use UAVs for ocean observation broadly, it will be necessary to enhance the capabilities of flight distance and payload.

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