Microphones on drones - Perspectives for soundscape

The concept of the soundscape is defined as the combination of all natural and artificial sounds, within a given area and associated temporal and spatial variations. Soundscape methods are especially important near airports and highways, where sound affects the quality of life and health. Soundscape methods are also used for security as they can detect gunfire, sounds of human abnormal behaviors and threats of terrorism, crime, riots, and animal sounds. Current soundscape approaches use stationary microphones and microphone arrays that have been limited to small areas. The application of microphone arrays installed on Unmanned Aerial Systems (UAS) can provide fast and low-cost soundscape of large areas. We present the results of our initial investigations of two systems: a four-microphone recording system installed on a Multirotor DJI S1000 and a two-microphone compact system installed on a Parrot Disco FPV fixed-wing drone. In the field test with DJI S1000, the cross-correlation method for direction finding of a source of sound allows the detection and tracking of a speaker producing noise with a level of 94 dBA at 1 m at a distance of about 10 m. Fixed wing drones are quieter and more suitable for studying the soundscape. They produce stable harmonics during the flight that can be filtered out for soundscape measurements. The sound pressure level measured by its microphones was about 72 dBA and drops down to 62 dBA when discrete harmonics were removed. The additional signal processing can decrease this self-noise level. The Parrot can provide sound recording during gliding, when the motor noise is absent.