Dispersion Imaging Scheme (The Phase-Shift Method) (Park et al., 1998a)
A multichannel field record (a) is first decomposed via Fast Fourier Transformation (FFT) into individual frequency component, and then amplitude normalization is applied to
the each component (b). Then, for a given testing phase velocity in a certain range (for example, 10 m/sec-2000 m/sec), necessary amount of phase shifts are calculated to
compensate for the time delay corresponding to a specific offset, applied to individual component, and all of them are summed together to make a summed energy of (c). This
is repeated for different frequency components. Display of all summed energy in frequency-phase velocity space will show patter of energy accumulation that represents the
dispersion curve as shown in (d). If input field record contains multi-modal dispersion, that behavior will appear as multiple energy accumulations occur for a given frequency
as whoen in (e).