43 2. Refraction surveying a b c d Figure 2.5 Head wave coefficient. The geometric spreading component G must be removed to detect the amplitude variations related to changes in the refractor. In the case of an irregular interface, the refracted wave can be corrupted by converted or diffracted waves, which introduce distortions of the refracted signal. The distortion of the refracted P-wave can be measured by a qualitative dimensionless attribute known as the Shape Index (Ic), which is given by the ratio A2+A3 to A1 where A1, A2 and A3 are the amplitudes of the first three picks of the refraction wavelet. Use of the Shape Index
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