Time measurement technique in ultrasonic inspection.

Fourier Transform - phase - slope determination of delta time between received RF burst (T2-R)-(T1-R),where T2 and T1 EMATs are driven in series to eliminate differential phase shift due to probe liftoff.

Slope of the phase is determined by linear regression of weighted data points within the signal bandwidth and weighted y-intercept. The accuracy obtained with this method can exceed one part in one hundred thousand.