f-k Filter and Deconvolution
Real data have noise of various kinds. Some signal enhancement programs are used prestack (before stacking) and some are used post-stack (after stacking CMPs). In the previous chapter, we used gain and band-pass filtering on prestack data. We only used one option out of many in sugain, but you are free to test other sugain options. In this chapter, we present two popular signal enhancement tools. These tools could prove useful in processing the Taiwan data set; however, we were unable to improve that data set using them. (Perhaps you can find a way!). To demonstrate their capability, we use them on Oz files (shot gathers) that we get from the Colorado School of Mines Center for Wave Phenomena web site (Section 3.3).
The first tool is a frequency-wavenumber (f-k) filter, a two-dimensional filter. We see how to use an f-k filter through the sudipfilt program. For a brief description of the f-k domain, see Sheriff (2002): f-k domain.
The second tool is deconvolution. We implement a deconvolution (decon) script that uses suacor, an autocorrelation program, and supef, a prediction-error filter.
In Section 10.4.1, we used the one-dimensional transform display script fxdisp. Script fxdisp transforms each trace from a time series to a frequency series. Here, we use interactive script ifk to apply a two-dimensional frequency filter. The f-k filter slopes can be specified in relative units of time over trace spacing (for example, seconds/meter) or in absolute units of time samples per trace. In this section, we specify the
Figures & Tables
Our objective is to introduce you to the fundamentals of seismic data processing with a learn-by-doing approach. We do this with Seismic Un*x (SU), a free software package maintained and distributed by the Center for Wave Phenomena (CWP) at the Colorado School of Mines (CSM). At the outset, we want to express our gratitude to John Stockwell of the CWP for his expert counsel.
SU runs on several operating systems, including Unix, Microsoft Windows, and Apple Macintosh. However, we discuss SU only on Unix.
Detailed discussion of wave propagation, convolution, cross- and auto-correlation, Fourier transforms, semblance, and migration are too advanced for this Primer. Instead, we suggest you refer to other publications of the Society of Exploration Geophysicists, such as “Digital Processing of Geophysical Data – A Review” by Roy O. Lindseth and one of the two books by Ozdogan Yilmaz: “Seismic Data Processing,” 1987 and “Seismic Data Analysis,” 2001.
Our goal is to give you the experience and tools to continue exploring the concepts of seismic data processing on your own.
This Primer covers all processing steps necessary to produce a time migrated section from a 2-D seismic line. We use three sources of input data:
Synthetic data generated by SU;
Real shot gathers from the Oz Yilmaz collection at the Colorado School of Mines (ftp://ftp.cwp.mines.edu/pub/data); and
Real 2-D marine lines provided courtesy of Prof. Greg Moore of the University of Hawaii: the “Nankai” data set and the “Taiwan” data set.
The University of Texas, the University of Tulsa, and the University of Tokyo collected the Nankai data. The U.S. National Science Foundation and the government of Japan funded acquisition of the Nankai data.
The University of Hawaii, San Jose State University, and National Taiwan University collected the Taiwan data. The U.S. National Science Foundation and the National Science Council of Taiwan funded acquisition of the Taiwan data.
Chapters 1–3 introduce the Unix system and Seismic Un*x.
Chapters 4–5 build three simple models (complexity slowly increases) and acquire a 2-D line over each model. (These chapters may be skipped if you are only interested in processing.)
Chapters 6–9 build a model based on the previous three, acquire a 2-D line over that model, and process the line through migration.
Chapters 10–11 start with a real 2-D seismic line of shot gathers (Nankai) and process it through migration.
Chapters 12–13 and 15–16 start with a real 2-D line of shot gathers (Taiwan) and process it through migration.