PROCESS GAINS, GAINS2, GAINS3 ------- ----- ------ ------ Parameters, alphabetically: addwb alpha etime fno lno rscale subwb tadd tgp tmult type v winlen Document Date: 20 June 2011 Updates: Add TYPE 10 (20log(t*v) - ver 2011.2.17 (20 June 2011) Add parameter v - ver 2011.2.17 (20 June 2011) Allow GAINS2 and GAINS3, January 2007 Complex modulus changes the sample interval. March 2005 Have TGP honor SUBWB, March 2004 Add parameter WINLEN (amplitude running average), June 2003 Add TADD and TMULT (time add and multiply), Oct 2000 Add TGP (time gain pair), July 2000 Add ADDWB, July 2000 Process GAINS applies a gain function. Chapter 4 of Claerbout's "Imaging the Earth's Interior" mentions several of the gain functions implemented. At least one parameter list must be given, even if no parameters are specified, in order that the parameter presets be set. e.g. gains end end PARAMETER DICTIONARY --------- ---------- TYPE - The type of gain to apply. = 1, a(i) = a(i) * (t*1000.)**alpha ( USGS gain ) where a(i) is the trace and t is the time of the trace sample in seconds. Restrictions: All traces must have the same start time. Preset = 1 = 2, a(i) = a(i) * (ABS(range)/SIGN(rscale,range)) ** alpha when ABS(range) .GE. rscale; where range is the range in the SEG-Y header, rscale and alpha are given by the user, SIGN is the Fortran SIGN function which means that ABS(rscale) is used when range is positive and -ABS(rscale) is used when range is negative. = 3, a(i) = a(i) * t ** alpha = 4, a(i) = a(i) ** alpha = 5, a(i) = a(i) * e ** (alpha * t) = 6, a(i) = SIGN(a(i)) * ABS(a(i)) ** alpha = 7, a(i) = SQRT(a(i*2-1)**2+a(i*2)**2) (modulus of complex trace) The only SEG-Y header value modified is the number of samples (since there are half as many samples after doing the modulus). The SEG-Y header value for the number of samples is divided by 2, as is the sample inetrval. The deep water delay is NOT modified. = 8, a(i) = a(i) * ABS(range/rscale) ** alpha when ABS(range) .GE. rscale; where range is the range in the SEG-Y header, rscale and alpha are given by the user. = 9, Time-Gain-Pairs. Automatically set to type 9 when parameter TGP (time-gain-pairs) is given. = 10, 20log(t*v). Spherical spreading in water decreases amplitudes by 20log(R), where R = t * v and t is the two-way travel time. Parameter ETIME is honored. Preset = none e.g. type 4 alpha 2 Additional Parameters: ---------- ---------- ETIME - The end time of the gain function types 1 and 10. Data after the end time will receive the gain of the end time. Types 1 and 10 ONLY. Preset = the last time of the first trace. e.g. etime 4. ALPHA - The exponent used in TYPEs 1 - 6 gain. Preset = 1. e.g. type 3 alpha 1.5 RSCALE - The range scalar used in TYPE 2 gain. Preset = 1. SUBWB - Subtract water bottom time switch. Type 3, 5 and 9 ONLY. = YES, The water bottom time is subtracted from the data time in the gain types that use time as a variable. e.g. a(i) = a(i) * t ** alpha becomes a(i) = a(i) * (t-wbt) ** alpha for t >= wbt Preset = NO TGP - Time-Gain-Pairs. A list of gains or multipliers to apply to each data trace. Time/gain not specified in TGP are obtained through extrapolation and interpolation of TGP. The gain for data times between TGP times will be linearly interpolated using the adjacent time and gain pairs. Times prior to the first time of TGP will use the first gain. Times after the last time of TGP will use the last gain. Preset = none e.g. tgp 0 1 1 10 2 100 ADDWB - When given a value of YES, the times given via TGP will be added to the water bottom time of the trace. (Water bottom times may be entered via PROCESS WBT). Valid with type 9 or TGP gains only. Preset=no e.g. addwb yes TMULT - Time multiplier used in gains type 3 and 5. Preset = 1. TADD - Time additive used in gains type 3 and 5. Preset = 0. When using a(i) = a(i) * t ** alpha, first t is: t = delay; if subwb == yes then t = delay - water_bottom; t = t * tmult + tadd (note that arithmetic is done left to right) WINLEN - The window length, in seconds, of an amplitude running average. The averaging is independent of gains 1-9 and is done AFTER the other gains. e.g. alpha 2 type 4 winlen .02 is also called the trace ENVELOPE. Every amplitude is squared and then a running average over 20 mils. is done. The window average is placed at the center of the window. Preset = none. V - The velocity in converting time to depth for spherical spreading in TYPE 10. TL = 20log(R), where R = t * v. Preset 1500. FNO - The first shot/rp number the parameter list applies to. Data (shots/rps) before FNO WILL NOT HAVE GAINS APPLIED. Preset = the first shot/rp received. e.g. FNO 101 LNO - The last shot/rp number the parameter list applies to. Data (shots/rps) AFTER LNO WILL NOT HAVE GAINS APPLIED. Preset = the last shot/rp received. e.g. LNO 101 Copyright (C) 1990 Seismic Reflection Processors, Solana Beach, CA. Written by Paul Henkart. ALL RIGHTS RESERVED.Go to the list of seismic processes. Go to SIOSEIS introduction.