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 aperx=nxt*dxt/2  	migration lateral aperature 			

 angmax=60		migration angle aperature from vertical 	

 v0=1500(m/s)		reference velocity value at surface		

 dvz=0.0  		reference velocity vertical gradient		

 antiali=1             Antialiase filter (no-filter = 0)               

 jpfile=stderr		job print file name 				

 mtr=100  		print verbal information at every mtr traces	

 ntr=100000		maximum number of input traces to be migrated	



 Notes:								

 1. Traveltime tables were generated by program rayt2d (or other ones)	

    on relatively coarse grids, with dimension ns*nxt*nzt. In the	

    migration process, traveltimes are interpolated into shot/gephone 	

    positions and output grids.					

 2. Input traces must be SU format and organized in common shot gathers

 3. If the offset value of an input trace is not in the offset array 	

    of output, the nearest one in the array is chosen. 		

 4. Amplitudes are computed using the reference velocity profile, v(z),

    specified by the parameters v0= and dvz=.				

 5. Input traces must specify source and receiver positions via the header

    fields tr.sx and tr.gx. Offset is computed automatically.		





 Author:  Trino Salinas, 05/01/96,  Colorado School of Mines



 This code is based on sukzmig2d.c written by Zhenyue Liu, 03/01/95.

 Subroutines from Dave Hale's modeling library were adapted in

 this code to define topography using cubic splines.



 This code implements a Kirchhoff extraplolation operator that allows to

 transfer data from one reference surface to another.  The formula used in

 this application is a far field approximation of the Berryhill's original

 formula (Berryhill, 1979).  This equation is the result of a stationary

 phase analysis to get an analog asymptotic expansion for the two-and-one

 half dimensional extrapolation formula (Bleistein, 1984).



 The extrapolation formula permits the downward continuation of upgoing

 waves  and  upward  continuation  of  downgoing waves.  For upward conti-

 nuation of upgoing waves and downward continuation of downgoing waves,

 the conjugate transpose of the equation is used (Bevc, 1993).



 References :



 Berryhill, J.R., 1979, Wave equation datuming: Geophysics,

   44, 1329--1344.



 _______________, 1984, Wave equation datuming before stack

   (short note) : Geophysics, 49, 2064--2067.



 Bevc, D., 1993, Data parallel wave equation datuming with

   irregular acquisition topography :  63rd Ann. Internat.

   Mtg., SEG, Expanded Abstracts, 197--200.



 Bleistein, N., 1984, Mathematical methods for wave phenomena,

   Academic Press Inc. (Harcourt Brace Jovanovich Publishers),

   New York.



=head2 User's notes (Juan Lorenzo)
untested

=cut


=head2 CHANGES and their DATES

=cut

use Moose;
our $VERSION = '0.0.1';


=head2 Import packages

=cut

use aliased 'App::SeismicUnixGui::misc::L_SU_global_constants';