Optical Processing, 3

When in seismic, the FREQUENCY of an event (of a seismic record or time section) is immediately thought of in terms of the time interval separating two successive peaks (or troughs). Its increase corresponds to TEMPORAL FREQUENCY ; for a sloping event this interval is measured by following a vertical axis because it corresponds to the time axis. In optical filtering, the only frequency which is taken into consideration is the SPATIAL FREQUENCY : this measures on the perpendicular to alignments on the section ; as a consequence, for a given frequency (time), the spatial frequency is proportioanl to the secant (1) of the apparent angle of dip on the section ( Fig. 4 ). It may be easily demonstrated that the points on the corresponding diffraction figure of one frequency time in placed on a horizontal line of which the distance to the horizontal axis is proportional to that of the same frequency. That is, given θ the angle made between the centre of the diffraction spot and the vertical and, also the dip of the corresponding lines. R - the distance OT H - the distance from T to the horizontal axis.