3d Seismic Ray Tracing Facility

Syntax Summary

d3time2depth [help=] [-h | ? | [ -help ]

[in= dds_vel_dict]

[norms= ray_starting_info]

[time_section= out_travel_time] [verbose=]

[save_rays= yes | no]

[axis= x y z ]

[size.x= Number_of_Pts_in_x_direction]

[delta.x= Increment_between_Pts_in_X]

[origin.x= X_axis_Origin]

Three dimensional ray tracer for modeling and migration of surfaces using the dds i/o system. d3time2depth traces rays from the surface z=0 to the subsurface determined by following rays until the travel time along the ray is equal to the traveltime of a ray from the surface to the reflector in the direction specified by the PtNorms file. d3time2depth accepts the following command line arguments of the form arg_id= arg_value

• help= causes this help message to be printed. The "help" information is also printed if any of the flags "-h ? or -help" are present.
• in= dds_vel_dict identifies the velocity file data dictionary
• norms= surface_at_depth identifies the name of the output file specifying the output surface and the surface normal directions. This file can be used as input for the program 3ddepth2time.
• time_section= time_file_name identifies the input file containing ray starting locations and directions.
• save_rays=y causes to program to compute and output ray paths into the file
  • ray.trajectory - ascii format
  • real.rayparms.rs - gocad++ format
• axis= x y z causes the labels "x", "y", and "z" to be applied to the three integer coordinate axes of the velocity model. Other possible values for labels are: axis = East North Depth, or axis= x y t.
• size.x= nx specifies that the velocity model has nx values in the "x" direc tion.
• size.y= ny specifies that the velocity model has ny values in the "y" direc tion.
• size.z= nz specifies that the velocity model has nz values in the "z" direc tion.
• delta.x= dx specifies that the size of the increments between stations of the velocity model in the "x" direction is dx (and similarly in the y and z directions)
• origin.x= x0 specifies the origin of the velocity model in the "x" directio n (and similarly in the y and z directions)

ix = Int((x-x0)/dx) +1

rx = (x-x0-(ix-1)*dx)/dx

where x is the x location of a ray, ix is the maximum index of any velocity station having a smaller x value than the ray, ix+1 is the minimum index of any velocity station having an x coordinate larger than the ray, and rx is the relative weighting factor for linearly interpolating between v(ix) and v(ix+1). That is, v(x)= v(ix)*(1-rx)+ v(ix+1)*rx. The program uses trilinear interpolation to obtain values of velocity between velocity stations in the 3d velocity field and bilinear interpolation to obtain gradient values. That is, the program uses the above formula to interpolate in however many dimensions that are appropriate.

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dvasicek@trc.amoc o.com

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