An array is a pattern of sensors that receives a signal. Arrays have been studied in a wide variety of disciplines. The manner in which the array samples and modifies the signal is a basic part of survey design and is often either neglected or casually considered. For the seismic application, the array sums the signals from a pattern of geophones. The purpose of the sampling and summing is to attenuate source-generateda nd off-line noise while preserving as much of the signal as possible.
Seismic arrays are a special case of generalized wave theory for arrays. General wave theory in this context deals with a propagating wavefront at an arbitrary velocity encountering an array of receivers. Seismic arrays, however, are usually in-line with the source, allowing for some simplification. When the survey becomes 3-D, this simplification does not always apply. Since the individual geophones in the array patterns are summed before the data are seen, the effect of the array may not be realized. On occasion, a high-resolutions urvey with high sourcef requencies, many channels, and close receiver spacing is defeated by the array. The design of the array is a delicate balance between the signal-to-noise (S/N) ratio and resolution. The array design is important enough to consider a case history that illustrates the effect of arrays on resolution.
Figures & Tables
“Written for both the nongeophysicist and the practicing geophysicist, this book collects many of the formulas, principles, concepts, and field approximations of seismic survey design. The basics of 2D and 3D design in this book offer an introduction to the nongeophysicist and provide a good review for the practicing geophysicist. Arrays, obstacles, and special problems are discussed, as are aspects introduced by 3D surveys. The author explores design attributes such as fold, costs, and field time.”