Distance to targets is basic and very important information. The time-lag between transmitted and reflected wave is typically used for distance estimation, but the estimation of short distance is usually difficult. The method using standing wave to measure short distance is known in the field of microwave radar. We have expanded this method to audible sound, and have shown the validity of the proposed method through simulations and experiments in an actual sound field of building.
Standing wave contains information on distance, because it occurs by the interference between transmitted and reflected sound. The power spectrum of observed signal has periodicity with periods corresponding to each distance to targets. Therefore, the distance is estimated through the range spectrum obtained by applying Fourier transform again to the power spectrum. Similar methods to the proposed one include cepstrum analysis and autocorrelation function. This paper shows fundamental consideration on distance estimation using standing wave of audible sound, including a comparison with these methods.