To measure environmental noises, many noise measurement and mapping systems have been studied. However, these systems are costly because many measurement points are required to construct a detailed and three-dimensional noise map. In recent years, with advances in unmanned aerial vehicle (UAV) technology, a multirotor aircraft has been frequently used as general use. Although it could be applied to acoustic measurements, it causes loud noise as it must always rotate its propellers during flying. Herein, a noise and spatial mapping system with a blimp robot is proposed. The proposed system achieved a silent, slow, and omnidirectional movement with a balloon filled with helium gas. Furthermore, the simultaneous localization and mapping (SLAM) technique is applied for the system's positional tracking and surrounding spatial mapping with a stereo camera. To evaluate our system, three experiments were conducted. First, the propeller rotational noises of the proposed system were compared to a general recreational-use multirotor. Next, the acoustical effects of a blimp, such as reflection and diffraction, were measured to decide the microphone position. Finally, a preliminary experiment was conducted to construct a simple three-dimensional noise map in a large experimental room. The results show that the proposed system could construct a three-dimensional indoor noise map by combining the sound information and the positional information.

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Recently, Unmanned Aerial Vehicle (UAV) is used in various situations and research fields, because of low cost and high convenience. For instance, there are many measurement and monitoring systems for taking environmental information by analyzing the image data which is acquired from the air with the UAVs. The UAVs with some propellers, such as quadcopter, always needs to rotate the propellers during flying. The noises of rotating propellers and makes collecting sound information with UAV difficult. In this study, we proposed the environmental sound recording system using a blimp which is filled with helium gas. The system has four propellers in the horizontal direction and two propellers in the vertical direction. This system has also a control board which has a SoC (including both FPGA and CPU) with embedded Linux OS to control six DC motors attaching to the each propeller and to communicate with PC through wireless LAN. The control board can record a sound signal with an A/D converter and an external memory. The experimental results show that it is efficient to make noise maps in horizontal and vertical planes by using the proposed system.