PROCESS FKMIGR
                              ------- ------

Parameters, alphabetically:
deltat   deltax    nfint     vel

Document Date: 18 July 2007
Modifications:  18 July 2007 - Increase maximum samples in to 16834.

Process FKMIGR performs F-K migration on data that is in the frequency-
wavenumber domain.  The data must have been through process TX2FK prior
to FKMIGR.  The output from FKMIGR is also in the F-K domain, thus, the
data may be transformed to the time-space domain via process FK2TX after
process FKMIGR.

F-K migration assumes a constant velocity for the entire section. This 
type of migration also assumes that the data is "zero-offset" data.  
Single channel data with fairly small shot-receiver distance are zero-
offset.  Moved out data are zero-offset.  The zero-offset diffraction 
hyperbola that are collapsed by F-K migration  have the formula
tx=2*sqrt(t0**2/4+x**2/v**2).

At least 60 traces should added to the beginning and the end of the 
section to be migrated in process tx2fk (parameter nxpad).  This padding
should be sufficient to prevent "edge" or boundary effects.

Fkmigr uses Stolt's algorithm to perform migration in the F-K domain and
may be found in "Imaging the Earth's Interior", by Jon Claerbout.

Prestack FKMIGR may be done by using the process TX2FK parameter PRESTK.

The deep water delay is honored by making t0 the delay time.  All traces
to be migrated must have the same delay however.

FKMIGR can not handle more than 32768 frequencies (which corresponds to
16834 sample in the time domain).

PARAMETER DICTIONARY
--------- ----------

VEL    - The constant velocity to use to migrate the data.
         Required       e.g. Vel 1500.

NFINT  - The number of adjacent frequencies to use in interpolation.
         Preset =10     e.g. Nfint 2

DELTAX - The distance between traces.
         Preset 1.      e.g. Deltax 6.25

DELTAT - The time sample interval, in seconds.
         Preset = trace header.   e.g.  Deltat .001   

END    - Terminates each parameter list.

Written and copyrighted (c) by:
Paul Henkart, Scripps Institution of Oceanography, December 1983
Rewritten by Alistair Harding, 1988
All rights reserved.