Fig. 12
(After Briggs 1993) Part a of this figure illustrates a changing pattern E(x, t) moving past two antennas separated by distance ξ 0 with velocity V to produce records E 1(t) and E 2(t). Part b shows the cross-correlation function ρ 12 calculated from E 1(t) and E 2(t) that takes a maximum value a lag τ m , smaller than the “correct” value \( \frac{\xi_0}{V} \) because of these changes, and consequently, an overestimation of the correct velocity V, the “apparent” velocity V a is produced