Patent ID: 7617731

Claim:
An ultrasonic measuring method for estimating at least one of the propagation distance and the propagation azimuth of a desired ultrasonic wave, which is one of a number of ultrasonic waves that have been transmitted by a spread spectrum technique using mutually different codes, the method comprising the steps of: (A 1 ) receiving the ultrasonic waves, which have been transmitted by the spread spectrum technique using the mutually different codes, at first and second receivers, thereby generating first and second received signals, respectively; (B 1 ) despreading the first and second received signals with a code that has been used to spread any of the ultrasonic waves other than the desired one, thereby generating at least one despread signal; (C 1 ) extracting a plurality of signals, of which the amplitudes are equal to or greater than respective threshold values, from the despread signal using the threshold values, thereby generating mutually different interference signals for the respective threshold values; (D 1 ) spreading the interference signals with the code that has been used to spread the ultrasonic wave other than the desired one and then removing the interference signals from the first and second received signals, thereby generating first and second received signals, from which the interference signals have been removed, for the respective threshold values; (E 1 ) despreading the first and second received signals, from which the interference signals have been removed, with the code of the desired ultrasonic wave, thereby generating first and second despread received signals, from which the interference signals have been removed, for the respective threshold values; (F 1 ) calculating maximum correlation values between the first and second despread received signals for the respective threshold values; (G 1 ) determining at which of the threshold values the greatest one of the maximum correlation values has been obtained; and (H 1 ) calculating at least one of the propagation distance and the propagation azimuth of the desired ultrasonic wave by the amount of time it has taken for the first and second despread received signals, associated with the threshold value determined, to reach the first and second receivers.