Fig. 2. (2.1) A waveform in water illustrating how the travel time is usually measured from the waveform. WINTDR measures from the apex of the bump to the end point located by the tangent lines. (2.2) The software of Heimovaara (1993) can either use a fixed start point based on cable length or can find the tangents for the first bump and calculate the travel time according to t_s = t_p - t_o.