GC3-D Design Philosophy – Part 4: The Even-Integer Rule*

Bob Hardage1

Search and Discovery Article #40664 (2010)

Posted December 17, 2010

*Adapted from the Geophysical Corner column, prepared by the author, in AAPG Explorer, December, 2010, and entitled “Last Call: The Even-Integer Rule”. Editor of Geophysical Corner is Bob A. Hardage ([email protected]). Managing Editor of AAPG Explorer is Vern Stefanic; Larry Nation is Communications Director.   Click for remainder of series:  Part 1  Part 2  Part 3

1Bureau of Economic Geology, The University of Texas at Austin ([email protected])

Even-Integer Rule

This article is the fourth of a four-article series. The final guideline that should be used when designing a 3-D survey is the use of the even-integer rule for specifying the exact dimensions of a recording swath. This design principle can be stated as:

A recording swath should span an even number of receiver lines and an even number of source-line spacings (Figure 1).

This rule defines how wide a 3-D recording swath should be in the inline and cross-line directions so stacking fold is a constant, non-oscillating value across 3-D image space. This even-integer rule does not replace the previously described concept of using the depth of the primary imaging target to define the size of the recording swath; the rule merely adjusts swath dimensions by small amounts to ensure a uniform stacking fold is achieved. For example: If the depth and size of the primary imaging target cause a designer to define the in-line dimension of the recording swath to be 14,000 feet and the receiver station spacing to be 110 feet, the even-integer rule might make a designer adjust the inline dimension to 13,200 feet (120 receiver stations) or to 14,080 feet (128 receiver stations), depending on how many receiver stations occur between adjacent source lines. When applied in the cross-line direction, the even-integer rule says the recording swath should span an even number of receiver lines. For example, a recording swath consisting of eight, 10 or 12 receiver lines is better than one consisting of nine, 11, or 13 lines. Note that the wording of the rule uses the phrase, “should span,” not the more restrictive condition, “must span.”

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