5/21/2023 0 Comments Red recodign time calc![]() The earlier figure showed rays and the previous figure shows traces resulting from a single six-fold CMP gather depicting reflections from a single flat interface (these could be from any of the subsurface locations from the zero-offset figure). ![]() ![]() The fold of the stack is determined by the number of traces in the CMP gather. The traces are then summed ( stacked) so that superior signal-to-noise ratio to that of the single-fold stack results. In the adjacent figure source points are shown in red and receiver points in green. The general idea of the method is to acquire a series of traces ( gather) which reflect from the same common subsurface mid-point. Neither of the two names exactly describes the method, so while both are equally invalid, CMP is usually preferred. The same method is also called Common-Depth-Point (CDP). In order to overcome the noise problem and additionally to estimate earth velocity, the method of acquisition most commonly used is the Common-Mid-Point (CMP) method. The zero-offset concept is an important one and the method might be used in practise if noise could be ignored. The resulting seismic data will be single-fold because there will only be a single trace per sub-surface position. Such an experiment would be called a zero-offset experiment because there is no offset distance between source and receiver (both marked as a yellow dot on the figure). The simplest type of acquisition would be to use a single coincident source and receiver pair and profile the earth along a line as shown in the adjacent figure. The contents of this chapter are fundamental to seismic processing. In this section we introduce the concepts of seismic acquisition, starting with a simple ray-based concept and ending with more practical details of the typical systems in use today. SEISMIC ACQUISITION version 1.0 released 29/1/99
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