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                      PROCESS NMO, NMO2, NMO3
                      ------- ---  ----  ----

Parameters, alphabetically:
addwb     dstretch  fno       hires     ivtp      lno       
newx      opath     stretc    type      vadd      vintpl    
vmul      vtp       vtrkwb    xfactor


Document Date:  19 July 2012
Doc mods:
	Add parameter IVTP, May 2003
        Add parameter DSTRETCH, August 2002
        Add parameter XFACTOR, September 2008
        Add parameter HIRES, July 2012

Processes NMO apply a travel-time correction to each trace.  
Process NMO2 and NMO3 are identical to PROCESS NMO, enabling NMO to be
given three times in a job.  The following corrections are available:

1)  Normal MoveOut or NMO: T(0) = SQRT(T(X)**2 - X**2/V(T)**2)
2)  MoveIn or deNMO: T(X) = SQRT(T(0)**2 + X**2/V(T)**2)
3)  Slant MoveOut or SMO:  T(0) = T(X) + X/V
4)  XMO: MoveOut followed by MoveIn: T(0) = SQRT(T(X)**2 - X**2/V(T)**2)
    followed by: T(XEW) = SQRT(T(0)**2 + XEW**2/V(T)**2)
    

where x is the range (shot-receiver distance) in the SEG-Y trace header
and V is the velocity specified by the user.  It is usually thought that
all traces common to the same reflection point should have the same
velocity function.  Thus, the velocity function given by the user may be
specified at various points along the seismic line (control points).
Traces lying between the user specified control points are obtained
through interpolation of the adjacent specified velocity functions.  The
times associated with the velocity function may be relative to the water
bottom rather than time zero.

SPATIAL VARIATION OF VELOCITY FUNCTIONS
RPs that do not have a velocity function defined by the user are
assigned a velocity function generated by one of two spatial variation
schemes (parameter vintpl).  (Also see the document on spatial
variation.)

ISO-Velocity spatial variation (vintpl 1)
The program calculates the time associated with each velocity when the
velocities are the same. e.g. nmo
        fno 1 vtp 1500 0. 2000 .4 2500 1.0 end 
        fno 3 vtp 1500 0. 2200 .6 2400 1.1 end
     end
then rp 2 will get vtp 1500 0. 2000 .414 2450 1.050

Layer cake spatial variation (vintpl 2)
The program interpolates both the velocity and the time of each
velocity-time pair.  Every velocity function must have the same number
of pairs.  e.g.   nmo
        fno 1 vtp 1500 .2 1600 .4 2000 1.0 end
        fno 3 vtp 1450 0. 1800 .6 2100 1.1 end
     end
then rp 2 will get vtp 1475.0 0.100 1700.0 0.500 2050.0 1.050


The velocity function (VTP) applies to all shots/rps with FNO to LNO of
the parameter list (recall that each FNO/LNO list is terminated with the
word END).  Spatial variation is accomplished by giving multiple
FNO/LNO lists, each with a unique VTP and terminated with END.  The
velocity function is constant for all shots/rps from FNO to LNO.

*** Note ***  spatial variation of velocities with velocity inversions
has problems!!!!

Each parameter list must be terminated with the word END.  The entire
set of NMO parameters must be terminated by the word END.

     Process NMO2 is identical to PROCESS NMO, enabling NMO to be given
twice in a job.  e.g.  procs diskin nmo nmo2 diskoa end

THE PARAMETER DICTIONARY
--- --------- ----------

VTP    - Velocity-time-pairs.  A list of stacking velocity and two-way
         travel time (in seconds) pairs.  VTP must be given in each NMO
         parameter list.  A maximum of 25 pairs may be given.  Data
         times before the first given time in VTP are held constant from
         the first given time.  Likewise, data times exceeding the last
         given time in VTP are held constant from the last given VTP
         time.  Velocities and times with VTP MUST INCREASE.
         Default=none.  e.g. vtp 1490 1.0 2000 2.0

IVTP   - Interval velocity-time-pairs.  A list of interval velocity
         and two-way travel (thickness) time pairs.  Spatial
         interpolation is done before ADDWB is applied (before the 
         interval velocities are converted to rms velocities).  When
         using ADDWB YES, the first interval should have 0 thickness and
         a velocity of water.  Each IVTP function must have the same
         number of intervals described.
         Default = none   e.g.    ivtp  1500 0 1600 .1 1700 .05

FNO    - The first shot (or rp) to apply the velocities to.  Shot (rp)
         numbers must increase monotonically.
         Preset=1

LNO    - The last shot (rp) number to apply the velocities to.  LNO must
         be larger than FNO in each list and must increase list to list.
         Default=fno

VMUL   - Velocity multiplier.  Every velocity is modified so that:
         vel = (vel - vadd) * vmul + vadd
         Preset = 1.    e.g.  vmul .9

VADD   - Velocity additive.  Every velocity is modified so that:
         vel = (vel - vadd) * vmul + vadd
         Preset = 0.    e.g.  vadd -200

DSTRETCH - The maximum stretch allowed as a percentage of the ratio
         of the NMO over the zero offset time t0.  i.e. (tx-t0)/t0.
         Move-out of long ranges or shallow data change the frequency 
         of the waveform and will cause interference when stacked with
         short range traces.  (tx-t0)/t0 approximates the ratio df/f
         where f is frequency and df is the change in frequency due
         to NMO.
         Preset = not given    e.g. dstretch 50 

STRETC - The maximum amount of NMO (delta t), in seconds.  Data
         exceeding stretch will be muted.  Valid with NMO only (type 1).
         Preset =1.

ADDWB  - A yes/no switch.  YES indicates that the two-way water bottom
         time from SEG-Y trace header floating point word 50 will
         be added to each time of the velocity function, after spatial
         variation has been done.  
         Preset=no

TYPE   - The type of travel time correction to apply.
       = 1,  Normal MoveOut or NMO: T(0) = SQRT(T(X)**2 - X**2/V(T)**2)
       = 2,  MoveIn or deNMO: T(X) = SQRT(T(0)**2 + X**2/V(T)**2)
       = 3,  Slant MoveOut or SMO:  T(0) = T(X) + X/V
       = 4,  XMO or Normal MoveOut followed by MoveIn.  Requires
             parameter NEWX.
         Preset = 1     e.g. type 2

VINTPL - The type of velocity interpolation between successive velocity 
         control points.
       = 1, Velocity spatial interpolation according to "iso-velocity"
       = 2, Allows regions of constant velocity to be interpolated
         correctly, however VTP pairs must be equal across control
         points.
       = 3, "Iso-velocity" spatial variation except on the first velocity
         time pair, which is interpolated in both velocity and time,
         making the first velocity time pair (water bottom reflector
         usually) spatially smooth.
       = 4, Both the velocities and times are interpolated.  Each
         VTP function must contain the same number of points.
         Preset = 1 when VTP is give, = 4 when IVTP is given.

VTRKWB - Velocity Tracking Waterbottom.  When given a positive value,
         velocity interpolation is cued from the water depth at the source
         (long SEGY header word 16). This is typically the centerbeam
         depth value which is placed in the header during acquistion
         for each individual shot.  

         The value of VTRKWB is the maximum depth change between adjacent
         cmp gathers.  If the change in water depth exceeds VTRKWB, the
         new water depth is "bad" and the previous depth is used instead.
         
         Although each trace in a gather may have a different centerbeam
         depth values, the depth value from first trace will be applied
         to the entire gather to minimize static shift problems (process 
         gather normally sorts so that the trace with the smallest range
         is first).

         This option is useful during realtime shipboard processing and allows
         a pre-defined 2-D velocity field to be used during processing,
         with fno and lno values representing water depth, vtp pairs
         defining the stacking velocity function for a given water depth.
         This scheme allows more flexibility for varying velocities along
         a reflection line (as opposed to hanging a single velocity
         function from seafloor).
         Preset = -9999.0      e.g. vtrkwb 100.0

OPATH  - The pathname of an output file containing the velocity used in
         move out after spatial and temporal interpolation have been
         done.  Each seismic sample has a velocity associated with it
         and is written to OPATH.  The velocities are written in ASCII,
         one velocity per line, unless the last four characters of the
         pathname end with '.segy'.  When an SEG-Y file is written, the
         SEG-Y headers are the same as the input and the trace length
         is the same; the seismic samples are replaced with velocities.
         Preset = none  e.g.  opath velocities.1234

NEWX   - The constant range that all traces will be MovedIn when using
         TYPE 4.  The use of NEWX automatically changes parameter TYPE
         to be 4.  NEWX causes every trace to be MovedOut so that the
         trace is time corrected as if it was at normal incidence (x=0),
         and the MoveIn is applied so that the trace is time corrected
         as if it was at range NEWX (x=newx).  This could also be
         accomplished using processes nmo1 header nmo2, where nmo1 did
         nmo, header changed the range, and nmo2 did MoveIn to range 
         NEWX.
         Preset = none.   e.g.   newx 1000

XFACTOR - A ranger multiplier.  The SEGY specification for range is a
        thirty two bit integer.  If the range isi to be expressed
        with greater precision, such as centimeters, then the range
        can be multiplied by a factor of 100 in process geom and then
        removed in NMO by using xfactor .01.
        Preset = 1.

HIRES  - A yes/no switch when set to YES uses a polinomial interpolation
        of trace values to obtain "high resolution".  Normally, nmo uses
        the closest sample of the TX trace.  This is like resampling the
        data before NMO.  Shallow data recorded at too coarse a sample
        interval will have repeated amplitudes that result is a "square
        wave" appearance.
        Preset = NO             e.g.  hires yes

END    - Terminates each parameter list.


Written and copyrighted by:
Paul Henkart, Scripps Institution of Oceanography, April 1980 
ALL RIGHTS RESERVED.
Go to the list of seismic processes.      Go to SIOSEIS introduction.