PROCESS FLATEN

Document Date: 20 February 1987

Process FLATEN flattens the seismic line to user given time.  Each trace
is shifted from the water bottom (depth or time) to the user given output
time.  Any SEG-Y trace header word may be used as the water bottom time.
Water bottom depths may be converted to travel times by giving a velocity.

The original concept of flatten started with the SIO Sea Beam center beam
depth being used as the depth.  That depth is the depth directly under
the center of the ship (SEG-Y header word ihdr(16)), not at all what 
seismic really sees.  Next, the Sea Beam closest beam depth was put into
SEG-Y header word ihdr(107).  Finally, PROCESS WBT was modified to not
only use the closest Sea Beam depth, but to look forward and aft for the
shallowest depth.

The SIO single channel system started recording the SeaBeam depths in 
spring 1987 (Crossgrain 1).

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

OTIME  - The time, in seconds, of the of the water bottom after process FLATEN. 
         REQUIRED. e.g. otime 5.6 

VEL    - The velocity of the water column used to convert the water 
         depth to the water bottom time.  A zero velocity indicates that
         the header word is a time.  time = header / vel.  SIO Sea Beam
         uses 1500 m/s
         Preset = 0     e.g. vel 1500

HDR    - The index of the water bottom depth/time within the REAL SEG-Y
         header.  PROCESS WBT puts the water bottom time in hdr(50).
         Preset = 50

IHDR   - The index of the water bottom within the 16 bit SEG-Y trace 
         header. Use only if the water bottom depth/time is not in 
         word 16.
         Preset = 0     e.g.   ihdr 66

LHDR   - The index of the water bottom within the 32 bit SEG-Y trace 
         header. Use only if the water bottom depth/time is not in 
         word 16.
         Preset = 0     e.g.   lhdr 63

NAVE   - The number of trace depths to average across.  The depth for a 
         given trace will be the average the current trace and the 
         previous NAVE-1 traces.
         Preset = 1    e.g.   nave 5

FNO    - The first shot (or RP) to FLATEN.  Shot (RP) numbers must 
         increase  monotonically.

LNO    - The last shot (RP) to FLATTEN.  LNO must be larger than FNO in
         each successive parameter list. 

END    - Terminates each parameter list.

Copyrighted (c) and written by:
Paul Henkart, Scripps Institution of Oceanography, February 1987
All Rights Reserved.