To always maintain highly precise measurement without respect to a weather condition such as temperature, humidity, atmospheric pressure, wind, rain, snow, and fog when minute displacement of a monitoring object such as a rock is measured so as to prevent disaster due to falling rocks or a landslide by using an ultrasonic wave technique.
Two or more small size ultrasonic wave receivers 3, 4 are arranged on a monitoring object such as a rock 1, while an ultrasonic wave transmitter 2 placed at a fixed distance from the rock 1 transmits ultrasonic waves. A phase difference between a transmitted signal and a received signal is detected, and on the basis of the phase difference between the transmitted signal and the received signal, a phase difference comparison between the respective ultrasonic wave receivers 3, 4 is carried out, so that a small quantity of inclination or displacement of the monitoring object is detected, while a phase difference comparison between the respective ultrasonic wave receivers 3, 4 is carried out on the basis of the detected respective phase differences from the transmitted signal, so that influence of a weather condition can be canceled.
NAGAYAMA AKIJI
HIBI SUSUMU
KATAKURA KAGEYOSHI
FUKAMI AKIHISA
KANDA YOSHINOBU
FUSHIMI HITOSHI
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