www.pudn.com > Cshot.rar > NOTES
This example plots rays for primary reflections from all interfaces.
There are a lot of changes from the old version of cshot
for this example.
First, let's deal with file param1:
simplemodel :model file
4 :#interfaces in model
plotcolors :model colors file
m :first plot descriptor (mwq) ...SEE
don't care :well coordinates FILE
s :shooting mode (sd) NOTES...
geometry1 :recording geometry ..........
sg :second plot descriptor (sgq) ...THIS
r :job descriptor (rlt) DIRECTORY
don't care :output filename(s)
0. 80. :range of takeoff angles
1. :increment in takeoff angle
4000.0 6000.0 9000.0
10000.0 13000.0 :velocities
n :direct wave? (y or n)
:headwave interface numbers (1, 2, ...)
y :primaries? (y or n)
The numbers of the notes below refer to record numbers in file param1.
(4) To plot the model enter m here. We want to go on and plot some
rays so do not quit after plotting the model (ie don't enter mq).
(5) The file name describing the well must always be given in Record 5.
We are not concerned with well shooting here so put any name you
want - the file need not exist.
(6) This record defines the shooting mode. The choices are s (for surface
shooting) or d (for downhole shooting). Everything the old version of
cshot did can be considered as surface shooting. This example will be
an illustration of surface shooting. See later examples for downhole mode.
(7) The recording geometry is now specified in a separate file, named
geometry1 in this example. The locations of the shots
and receivers are specified in this
file. See below for a detailed description.
(8) You can choose to plot the source or receiver locations by entering
s or g or both (sg) here. In fact, you can enter sgq and quit at this
point. (So if you entered m in Record 4 and sgq in Record 8 you would
get a plot of the model along with the source and receiver locations,
and nothing else. If you choose to quit here, then Record 8 can be
the last line of file param1.) If you don't want to plot either the
shot or geophone locations then leave the first two columns of Record 8 blank.
(9) This is the job descriptor. To get a ray plot enter r here.
To get a listing enter l. For a time record (to be built later by
program cshot2) enter t. To get all three at once enter rlt, etc.
(10) First part of the name to be given to all output files. Doesn't matter
this time since no output files are being generated.
(11)-(13) Nothing new here, see old documentation.
(14) y to generate direct wave; n otherwise.
(15) You can ask for head waves by giving the refracting interface
numbers in Record 15. For example, enter 1 3 for head waves from
interfaces 1 and 3. Triplications in head wave arrivals are not
supported by the program: ASK FOR HEAD WAVES FROM REASONABLY FLAT
LAYERS ONLY. Leave blank for no head waves.
(16) y to generate primaries from all interface; n otherwise.
Now let's take a look at specifying the recording geometry. Here is
file model1cards:
1 1000. :reference station number and its x-coord.
200. 0. :station spacing and receiver depth
16 20 21 35 6. 0. :r1 r2 r3 r4 s sdepth --- shot 1
(1) First of all we specify a station number and define its x-coordinate.
All shot and receiver location numbers will be referenced to this station.
Here we say that station 1 is at x=1000.
(2) Record 2 contains the receiver spacing and the receiver depth (below
the upper surface).
Next come the geometries for all the shots - one record for each shot.
(3) Geometry of shot 1. The first four entries, which we can refer to
as r1, r2, r3 and r4, describe the receiver locations for this shot.
With four receiver entries we can specify a gap in the spread. r1 is
the station number of the first receiver in the spread. r2 is the last
receiver before the gap. r3 is the first receiver after the gap. r4 is
the last receiver on the spread.
A gapped spread might look something like:
50 100 120 170. The gap is between 100 and 120.
A spread without a gap might look like:
50 100 101 170. There is no gap between r2 and r3 here.
The fifth entry in Record 3 is the station location of the shot.
Note that this is a float, thus enabling us to position the shot in
between stations. For example, a shot postition of 10.5 is half way
between stations 10 and 11. With a gapped spread, we usually put the
shot inside the gap, e.g. 50 100 120 170 110. however, the shot
can be anywhere. The final entry in Record 3 is the shot depth.
Records 4 - n would describe shots 2 - (n-2). You need one record for
every shot. The program reads in one record at a time, computing the
described shot, until it reaches the end of the file.