Fig. 3. Computation of travel time error estimates using vertical moving windows: Borehole BB, 31 Mar. 2003. Note how the 1-m window, equal in size to the deployed antenna, overestimates the data error: within 1 m the trend in the data is clearly identifiable as a signal above the error level. On the contrary, arrival times within a window of 0.25 m are within the error range (0.5 ns).