On distance measurement using band-limited noise

In many engineering fields, distance to target is fundamental and very important information, and often estimated or measured by using sound. To measure the distance to the target, time delay between reflected wave from transmitted wave is often used. However, it is difficult to measure short distance. Actually, ultrasonic range finders and ultrasonic level meters have minimum detectable range. Meanwhile, in the research field of microwave radar, a range finding method using standing wave is known for measuring short distances. It seems effective to use the standing wave of sound wave for measuring short distances. Moreover, in an actual situation of acoustic measurement, a random noise is very often utilized as well as a pure tone. Therefore, we focus our attention on audible sound and examine the distance estimation method using standing wave in audible sound. Specifically, we perform a computer simulation when audible sound, e.g., white noise, is used as a transmitted wave.