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                               PROCESS TX2TP
                               ------- -----

Parameters, alphabetically:
fc       np       ohpath   pcnti    pcnto
prestk   sep      set      setau    shift

Document Date: 3 May 2007

PROCESS TX2TP transforms data in the time-space domain to the tau-p 
space using the "HOP" method for slant stacking refraction data" by
Henry, Orcutt, and Parker (GRL, Dec 1980). The problem of slant-stacking
seismic records at a number of ranges to synthesize a tau-p curve is 
posed as a linear inverse problem for fixed frequency.  Using an inner
product weighted by (k^2 + b^2)*k (where k is wavenumber and b some real
positive number), then the representers are Bessel functions of k*range,
scaled by 1/(k^2 + b^2), and the model is U(k,w) (vert comp only).  The
inverse of the Gram matrix can be found analytically as sums and 
differences of products of modified Bessel functions of b*range.

Since the tx to tau-p transformation changes the meaning of shots and
rps, TX2TP will output the data as if it is a shot containing np traces
headers will contain the following information:

record ("shot") number   (SEG-Y word 3)
trace number with the record  (SEG-Y word 4)
trace id flag (live trace flag)  (SEG-Y word 15)
p value*1000. (in the tx domain position for range)  (SEG-Y word 10)
tau*1000 of the first output sample (delay in ms) (SEG-Y word 55)
tau of the first output sample (delay in seconds) (SEG-Y word 46)
number of data samples (SEG-Y word 58)
sample interval in millihertz (instead of microseconds) (SEG-Y word 59)

The input data must be order so that the ranges are monotonically 

Limitations :      300 input time traces
                   1024 samples within a time trace
                   300 output p traces
                   400 tau's within a p trace
--------- ----------

SET    - The start and end times of the data to transformation.  Data 
         prior to the start time or after the end time will be omitted.
         Preset = the times of the first input trace.  e.g.  set 3 7

SEP    - Start and end p values to calculate.  The SEP range should only
         span the dip components of interest (Yilmaz pg 437).  The p 
         values are in units of kilometers - TX2TP converts the SEG-Y
         ranges from meters to kilometers.
         Preset = .2 .7  (1/5 1/1.4)   e.g.  sep .05 .55

SETAU  - The start and end tau's to calculate.  The first output sample
         will be at the start tau.
         Preset = delay  2*(power of two > nsamps) + 1

NP     - The number of p values to calculate.  NP is the increment 
         between the start and end p values.
         Preset = the number of input time traces

FC     - Cutoff frequency for calculating models.
         Preset = Nyquist frequency      e.g. fc 125

PCNTI  - Percent taper applied to the input data before the forward FFT.
         Preset = 0

PCNTO  - Percent taper applied to the models before the inverse FFT.
         Preset = 0

OHPATH - Output header pathname.  TX2TP saves all of the SEG-Y trace
         headers in a disk file so that the output tau-p traces have the
         same headers as the input.  The disk file is temporary unless 
         OHPATH is given.  This is particularly important if the data are
         converted back to tx in a separate SIOSEIS run.
         Preset = temporary file.    e.g.   ohpath txheaders.line1-2

SHIFT  - The time shift to apply to successive traces.  The shift is 
         accumulative, thus each trace is shifted by SHIFT relative to
         the previous trace.  The shift represents a constant reduction
         velocity, i.e. start time for each trace must be delayed by
         same amount relative to previous trace.  The input traces must
         have a constant range increment for this to work properly.
         Required.              e.g.  shift .05

PRESTK - When set nonzero, the transformation is done whenever the
         PRESTK number of "gathers" have been collected.  A "gather" is
         whenever the "end-of-sort" flag (SEGY header word 51) is -1.
         Processes SORT and GATHER set the "end-of-sort" flag.
         Other schemes using DISKIN and HEADER can be used also.
         Preset = 0.

Copyright (C) by The Regents of The University of California, 1988
Go to the list of seismic processes.      Go to SIOSEIS introduction.