Patent ID: 6151014
Filing Date: 2000-11-21
Classification: G01S

Abstract:
A method for tracking variations in distance D calculated from time-of-flight measurements of a sequence of pulses of a pressure wave oscillation from a transmitter to a receiver, the pressure wave oscillation having a given wavelength and wave period, the method comprising:(i) identifying a state of synchronous operation by obtaining at least two time-of-flight measurements derived from successive pressure wave pulses which satisfy given synchronicity criteria;(ii) monitoring successive time-of-flight measurements to identify a shifted time-of-flight measurement which varies by at least half of the wave period from a predicted time-of-flight value calculated from a number of preceding time-of-flight measurements;(iii) identifying a shift factor corresponding to an integer multiple of the wave period by which said shifted time-of-flight measurement must be corrected to obtain a corrected time-of-flight measurement falling within half of the wave period from the predicted time-of-flight value; and(iv) correcting the distance D calculated from said shifted time-of-flight measurement by the product of said shift factor and the pressure wave wavelength.