WindCompass: Determine Wind Direction Using Smartphones

Because of the rich set of sensors, smartphones have demonstrated their versatility in environmental awareness. Already a smartphone can act as a compass, a barometer, and a pedometer, but cannot behave as an anemoscope to measure the wind direction yet, which is useful to many outdoor activities. In this paper, we propose a creative approach to identify the wind direction purely using on-board sensors of a smartphone, i.e., a microphone and an orientation sensor. Our approach relies on the observation that the strength of the noises generated by wind blowing towards the microphone is symmetric to the incident angle of wind, and the symmetrical axis represents the wind direction. Thus, we built an app (called WindCompass) that lets user rotate a phone while recording acoustic signals to determine the wind direction. Granted that rotation velocities and background noises will affect the accuracy, we utilize noise filtering and symmetric restoring schemes to process the recording and propose a circular auto- convolution algorithm to identify the symmetrical axis. The algorithm is light enough to be implemented in smartphones and robust to modest measurement errors. Our experiments show that WindCompass achieves an average error less than 3º in a well-controlled motion, less than 10º for free motion, and less than 18º at a lake side, which is smaller than the range of sixteen principal bearings of wind direction commonly used in meterological observations.