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                                PROCESS SYN
                                ------- ---

Parameters, alphabetically:
delay     exthdr    fno       lno       noise     noinc
ntrcs     ntrgat    secs      si        ttva      tva
values    x         xinc

Document Date: 27 June 2011
Mods:  Add parameter EXTHDR, May 2003
       Add parameter NOINC, May 2006
       Add parameter TTVA, June 2007

PROCESS SYN creates a "spike" synthetic trace in the form of a shot 
consisting of a group of traces containing either user given trace
values or seismic events.  The seismic events are spikes placed in time
and amplitude according to user specified parameters and may be either
reflected or refracted events.

Each trace is assigned a range and the spikes may then be altered from
trace to trace according to the inverse normal moveout.  In other words,
the user specifies a set of time-velocity-amplitudes for zero offset and
PROCESS SYN then computes where the spikes are on each trace according 
to the formula tx=sqrt(t0*t0+(x/v)*(x/v)) or tx=abs(t0)+x/v where t0, x,
and v are specified through user parameters.

Synthetic shots are commonly filtered by process filter before being
processed further.

The synthetic parameters may be spatially varied.  Each parameter list
must be terminated with the word END.  The entire set of syn parameters
must be terminated by the word END.

--- --------- ----------

FNO    - The first shot number to create with the current syn parameters.
         Shot numbers must increase monotonically.

LNO    - The last shot number to create with the current set of syn
         parameters.  LNO must greater than or equal to FNO in each list
         and must increase list to list.

NOINC  - The increment between shot numbers.  e.g. DO fno, lno, noinc
         Preset = 1

TVA    - Time-velocity-amplitude tuples.  A set of triples describing
         the position of the spikes making up the 0 offset trace.  A
         negative time indicates that the event is a refracted event,
         whereas a positive time indicates a reflected event. A maximum
         of 30 triplets (90 numbers) may be given.
         Preset = none

TTVA   - Type-time-velocity-amplitude tuples.  A set of triples
         describing the seismic event to create.
         Type = 1, a hyberbolic event:  tx = sqrt(t0**2 + x**2/v**2)
         Type = 2, a linear event: tx = t0 + x/v
         time = the two-way travel time of the event at x = 0.
         Preset = none
         e.g. ttva 2 0 1500 1   1 .5 1500 1   1 .6 1550 1

VALUES - The list of trace values, each value separated from the other
         by a blank.  The values may be given on as many lines as
         necessary.  When the values are given in exponential format,
         positive exponents must have a + rather than a blank.  The
         first value given will be the first data value of the trace
         (i.e. the first value will be at time delay).  A maximum of
         90 values may be given.  Use process DISKIN parameter 
         FORMAT ASCII when more than 90 values are needed.
         Preset = none        e.g. values .5 1 .5 0 -.5 -.1E+1

SI     - Sample interval in seconds.

NTRCS  - Number of traces per shot.

SECS   - Shot length in seconds.

X      - The range of the first trace.  The units of x don't matter, so
         long as they are consistent with the velocities used.

XINC   - The range increment from trace to trace.  Trace 1 will have a
         range of x, trace 2 will have a range of x+xinc, trace 3 will 
         have a range of x+2*xinc,...

NTRGAT - The number of traces per gather.  When given non-zero, every
         NTRGAT trace will be flagged as the end of a gather (the 51st
         integer*4 word in the trace header).  Other traces will have
         the flag cleared to zero.  The use of ntrgat also sets the 
         binary tape header sort flag to 2 (sorted by rp) and the rp
         number (word 6) is set to the shot number (word 3).  The shot
         number and shot trace number (words 3 & 4) are set to 0 and the
         rp trace number (word 7) is set to the trace count in NTRGAT.

DELAY  - The deep water delay.  The value for delay is inserted into the
         SEG-Y trace header after the seismogram is created.  The times
         specified in tva must reflect the delay.
         e.g. tva .1 10000 1 delay 1  puts a spike at time 1.1

NOISE  - The level of white noise to add to the trace is made with 
         VALUES or TVA.  The level given multiplies the unit variance
         trace.  The seed for each trace is the shot number * 1000 plus
         the trace number.  See Numerical Recipes (Fortran) function 
         gasdev for the precise algorithm used.
         Preset = 0.

EXTHDR - The number of SEG-Y Rev 1 Textual Extension Records to create.
         All records will be blank, except the last one which has the
         "((EndText))" stanza.  Also see parameter EXTHDR in process
         Preset = 0        e.g.   exthdr 1

END    - Terminates each parameter list.

Written and copyrighted by:
Paul Henkart, Scripps Institution of Oceanography, July 1980
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