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Fig. 2. Example of error analysis on vertical radar profiling (VRP) data at the Trecate site. The black dots are the absolute values of arrival time differences obtained by rotating the transmitter antenna at the surface by 90° in azimuth. The gray continuous lines represent standard deviation of arrival times computed over moving windows of different size along the vertical direction. A comparison between moving window standard errors and difference in arrival times at different transmitter azimuth (around 0.5 ns) indicates that the actual resolution of VRP data at this site is about 25 cm. Data were collected at 5-cm vertical spacing.
