Patent ID: 8090547
Filing Date: 2012-01-03
Classification: G01S

Abstract:
1. An ultrasonic measurement method for measuring at least one of a propagation distance and a propagation direction of a selected ultrasonic wave among a plurality of ultrasonic waves that have been spectrum-spread with different codes, comprising: a step (A) of receiving the plurality of ultrasonic waves that have been spectrum-spread with different codes by first and second wave-receivers to produce first and second receive signals; a step (B) of de-spreading the first and second receive signals respectively with a selected code having been used for spreading the selected ultrasonic wave and a corresponding non-selected code having been used for spreading at least one non-selected ultrasonic wave which has not been selected from among the plurality of ultrasonic waves to thereby produce a selected de-spread signal and at least one non-selected de-spread signal for the first and second receive signals, respectively; a step (C) of obtaining an amplitude ratio between the selected de-spread signal and the at least one non-selected de-spread signal for each of the first and second receive signals; a step (D) of determining at least one threshold value based on the amplitude ratio for each of the first and second receive signals; a step (E) of extracting a signal having an amplitude greater than or equal to the threshold value from the at least one non-selected de-spread signal by using the threshold value for each of the first and second receive signals to thereby produce at least one interfering signal; a step (F) of, for each of the first and second receive signals, spreading the at least one interfering signal with a corresponding non-selected code and then removing the at least one interfering signal from the first and second receive signals to thereby produce first and second receive signals from which the interfering signal has been removed; a step (G) of de-spreading the first and second receive signals from which the interfering signal has been removed each with the selected code to thereby obtain first and second de-spread signals from which the interfering signal has been removed; and a step (H) of calculating at least one of the propagation distance and the propagation direction of the selected ultrasonic wave based on points in time at which the first and second de-spread signals from which the interfering signal has been removed arrive at the first and second wave-receivers, wherein the step (D) includes obtaining in advance a relationship between a threshold value and the amplitude ratio such that an S/N ratio of the receive signal from which the interfering signal has been removed is greater than or equal to a predetermined value, and determining a threshold value for an amplitude ratio based on the relationship obtained in advance.