Three-dimensional noise mapping system with aerial blimp robot

This paper presents a prototype system of a three-dimensional noise mapping system with an aerial blimp robot. The system's length is 1.5 m, its width is approximately 1.2 m, and its weight is approximately 850 g. The system is divided into two parts; one part is a balloon filled with helium gas, and the other part is a multirotor unit. Since the balloon helps to hover in the air without rotating propellers, the propeller rotation noise can be reduced. The buoyancy of helium gas is lighter than the system weight and therefore the system could return to the ground automatically, even when it is out of control caused by low battery or other problems. The multirotor unit has six propellers, which make enable omnidirectional motion. The multirotor unit also has a system control board with a field programmable gate array system on chip, which integrates central processing unit for controlling of propeller rotation, sound recording, and communicating with the host personal computer. The microphone for recording the sound is mounted at the middle of the balloon, to reduce the effect of propeller rotation noise. We evaluated the system two ways: a comparison of the propeller rotation noises between the system and a general multirotor, and an analysis of acoustical effect of the balloon. The result showed that the propeller rotation noise was reduced by 42 dB as compared with a general multirotor, and the balloon had large effects of the sound field when the balloon was placed between the sound source and the microphone. Finally, we measured the sound pressure level using the proposed system. The result showed that the proposed system can continuously measure sound pressure distribution in noise map space.