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 and ALL THE TX DOMAIN TRACE INFORMATION IS LOST. The SEG-Y trace 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 increasing. Limitations : 300 input time traces 1024 samples within a time trace 300 output p traces 400 tau's within a p trace PARAMETER DICTIONARY --------- ---------- 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 ALL RIGHTS RESERVED.Go to the list of seismic processes. Go to SIOSEIS introduction.