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# trunk/src/green/disan/greda
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(XXX macro: "PageOutline")
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Navigation: [[Mainpage], [wiki:trunk], [wiki:branches], [wiki:tags], [wiki:vendor], [wiki:export], [wiki:admin], [wiki:docs|WikiStart]]
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## Location
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**greda** is located at [source:trunk/src/green/disan].
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## Purpose
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Calculate Fourier-Bessel expansion coefficients for a single-shot seismic profile by using linear inverse theory.
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The theory behind this program is described by
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[[Forbriger (2003. Inversion of shallow-seismic wavefields: I. Wavefield transformation. Geophys. J. Int., 153, 719-734)|http://dx.doi.org/10.1046/j.1365-246X.2003.01929.x]] (doi:10.1046/j.1365-246X.2003.01929.x).
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## Features
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* calculates f,p-coefficients of a seismogram section by a slant-stack, Fourier-Bessel-transformation or Fourier-Hankel-transformation
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* different available alternatives to the Fourier-Bessel transform
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* definition of the frequency-slowness range
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* apply tapers to the input data
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* additionally parameters defining the expansion (Hankel function instead of Bessel functions, damping factors, ...)
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* phasor walkout
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* supports a variety of input formats including SeismicUn*x and raw ASCII (through wiki:trunk/src/libs/libdatrwxx)
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* ...
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Results can be displayed by [[grepg|trunk/src/green/grepg]].
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## Definition of the Fourier transformation
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The Fourier transformation used in this program and in
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related programs (like gremlin, syg, and gresy) is
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defined as
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` U(omega) = int_-infnity^+infnity u(t) exp(-i*omega*t) dt `
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Theoretical descriptions of wave propagation often use
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exp(i*omega*t) as transform kernel instead of exp(-i*omega*t)
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in order to make positive wavenumbers equivalent to wave
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propagation in positive coordinate direction. The Fourier
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coefficients calculated by this program consequently are
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the complex conjugates of those used in theory. Where
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`H^(2)_0` is used in theory, you have to use `H^(1)_0`
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in greda.
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## Inline help
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mscha@gpiag12:~>greda
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GREDA V3.22 Calculate Fourier-Bessel expansion coefficients
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Usage: greda datafile coeffile [[format] [-R|-ty]]
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[[[-K] [-P] [-D] [-M] [-H|-L]]]
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[[nslo] [-s smax] [-f fmax|-n]]
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[[frac] [-T frac] [-E edge|-t]]
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[[n,f] [-a] [-b] [-g|-W]]
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[[minoff] [-B delta] [-r expo] [-F|-O]]
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[[[-2] [-q f,e] [-Q f,e] [-S|-1]]]
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[[[-o] [-N f] [-X|-v]]]
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[[o1,o2,o3,o4|-tap]]
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[[filename|-spo]]
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[[f,p,file|-pw]]
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[[filename|-pwf]]
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[[filename|-pwa]]
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or greda -help
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or greda -xhelp
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STOP ERROR: missing parameters
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