notes

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                DEMO11 - Multiple Bounce Head Waves

Records 19 and 20 specify multiple bounce head waves.  The letter
h in Column 1 defines these events as head waves.  The integers
that follow are Interface numbers where reflections occur, and
the refractor number.  Record 19 describes rays that leave the source,
reflect from Interface 2, then reflect from Interface 1, then
intersect Interface 2 (the refractor) at the critical angle,
thus becoming head waves.  So, the last integer in the list 
specifies the refractor.
Record 20 describes rays that reflect from Interface 4 before
meeting a refractor (Interface 3 in this case).
Notice how the velocities allow these refractions to occur
in this model.  
(If you ask for a lot of bounces, you might
find that no rays are found.  This is often because the offset
between source and receiver well is not large enough. Multiple
bounces require larger offsets or the rays never go critical at
the refractor.)
Note that the refracted rays from Interface 2 go up, while the
refracted rays from Interface 3 go down, in this example.
This explains the move-out on the shot record.

smoothmodel                         :model file
4                                   :#interfaces in model
plotcolors                          :model colors file
m                                   :first plot descriptor (mq)
rwell1                              :receiver well coordinates
wg                                  :receiver plot descriptor (wgq)
d                                   :shooting mode (dg)
swell4                              :source well coordinates
don't care                          :file containing coords. of sources
ws                                  :source plot descriptor (wsq)
rt                                  :r to plot rays       
demo11                              :output file name
  0.  90.                           :range of takeoff angles 
1.  .1   2.                         :coarse, fine angle increment; ray density 
4000.  6000. 10000.  6000. 20000.   :velocities
n                                   :direct wave?
n                                   :primaries?
n                                   :head waves?
h  2 1 2                            :multiple bounce head wave
h  4 3                              :multiple bounce head wave