Robust acoustic distance measurement method based on interference in noisy environments

Distance to target is fundamental and very important information in many engineering fields. Many distance measurement methods with sound utilize the time delay of reflected wave which is measured with reference to transmitted one. This method, however, can not measure short distance because the transmitted wave, which has not attenuated enough as of reception of reflected waves, suppresses the reflected waves for short distance. Therefore we proposed acoustic distance measurement method based on interference between transmitted wave and reflected waves, which could measure distance in short range. However, the performance of our method was not discussed in noisy environments. In this paper, we focus discussion on noisy environments with additive noise. We describe our method using real measuring system in noisy environments. In addition, we propose suitable noise reduction for our method by applying an idea of synchronous addition and spectral subtraction in noisy environments. Finally, we confirm the effectiveness of our method using noise reduction through simulation and experiment. As a result, it has been confirmed that the distance can be measured at SNR = 5 or 15 dB by our method without using noise reduction and can be measured at SNR = -5 to 5 dB by our method using noise reduction.