VSP Demo--------VSP data is produced by setting off a number of sources at various depthsin a well.  Data is recorded at a line of receivers on the surface.A receiver sort is then performed on the data.  We can view the receiversort as equivalent to the standard VSP case, where the source is onthe upper surface and the receivers are inside the well.For cshot1 there are a few changes to be made in param1 and there is also another input file describing the well.First we change Record 7 of param1, the shooting mode, to d for downhole.Next we give the name of the file describing the well in Record 6.To plot the well enter w in column 1, 2 or 3 of Record 5.The rest of param1 follows the surface source case.The well file is called curvedwell2 in this example.  Here it is7000.                           :x-coord. of top of well7000.  2000.                    :x,z coord. pair down the well5000.  7000.                    :x,z coord. pair at bottom of well1.   -999999.                   :end of well definition500.                            :depth to first source25   200.                       :#sources, source spacingFirst we give the coordinates describing the well.  The top of the wellis defined by the x-coordinate where the well meets the upper surface.The z-coordinate of the top of the well is not provided (in general,for a curvy upper surface, it will not be known off hand).  A largenegative z-coordinate ends the well definition.  The program fits acubic spline through the well.  As with the interfaces, the well shouldnot be too curvy.  In any case, it should be single valued in z.For the downhole case we specify the source locations in the well fileand not in the geometry file.  The depth to the first source is given, alongwith the number of sources and the source spacing.  Depth here is reallyarc length down the well.  The program integrates down the well to findthe locations of the sources in space.The geometry file for this example is1         3700.                        :reference station number and x-coord.300.      100.                         :station spacing and receiver depth1  2  3  10         1.  200.           :shot 1 - r1 r2 r3 r4 s sdepthOnce again, in downhole mode the geometry file describes the line layout but not the shot locations.  Thus, the fifth and sixth entries in Record 3 here are not read and could be left out altogether.You can still move the spread around for different shots by specifying more records after Records 3.  However, the total number of geometry records does nothave to equal the number of shots requested in the well file.If there are more shots requested inthe well file than there are receiver geometries, then the programsimply holds the last geometry fixed for all remaining shots.Example.  10  shots requested,  10 geometry records provided.	  shot 1  uses geometry 1  (Record 3)	  shot 2  uses geometry 2	  ...	  shot 10 uses geometry 10Example.  10  shots requested,  2 geometries provided.	  shot 1  uses geometry 1	  shot 2  uses geometry 2	  shot 3  uses geometry 2	  ...	  shot 10 uses geometry 2 Example.  10  shots requested,  1 geometry provided.	  shot 1  uses geometry 1	  shot 2  uses geometry 1	  ...	  shot 10 uses geometry 1 The last example here is the typical one for VSP data, ie, we hold the receiversfixed for all shots.Now let's take a look at param2 for cshot2:r                                :job option (s OR r)10                               :first, last shot; OR receiver1  25                            :first, last trace; OR first last shot record10.  25.   35.  50.              :frequency spectrum of wavelet.150                             :wavelet length (secs).004                             :sample rate (secs)2.                               :record length (secs)demo12shot                       :input filenamedemo12traces                     :output filenameThe only changes here are in Record 1, where a receiver sort has been requested,and in Record 2 where the receiver number is specified (one receiver sort only).Receiver 10 is the closest receiver to the well in this particular exampleand Receiver 1 is the farthest away from the well.cshot2 is run three times in the demo.  The trace plots show how the VSP changesas we move away from the well (sorts are carried out for Receivers 10, 6 and 1).