Wave-equation Migration Velocity Analysis using Plane-wave Common Image Gathers

Bowen Guo

2017.03.06

Figure 1 (a) True velocity model and (b) inverted velocity model starting from a homogeneous velocity of 1.5 km/s by PWEMVA method after 20 iterations.

1 Objective

2 Prerequisties

• FFTW (http://www.fftw.org/), the software library for computing discrete Fourier transforms (DFTs). You can install it as follows,

  
  shell$ ./configure --prefix=YOUR_FFTW_DIRECTORY --enable-float --enable-shared --enable-threads --enable-openmp --enable-mpi
  shell$ make
  shell$ make install
  
  
  
  

After finishing installation, set the environment variables. Add following environment variables to your ~/.bashrc,

• 
  #FFTW 
  FFTWDIR=YOUR_FFTW_DIRECTORY 
  PATH=$FFTWDIR/bin:$PATH 
  export FFTWDIR  
  export LD_LIBRARY_PATH=$FFTWDIR/lib:$LD_LIBRARY_PATH
  
  
  
  

Finally, 

• 
  shell$ source .bashrc
  
  
  
  

• Madagascar, which is an open-source software package for multidimensional data analysis and reproducible computational experiments. To install Madagascar please refer to http://www.ahay.org/wiki/Installation.
• Open MPI (https://www.open-mpi.org/software/ompi/v1.6/downloads/openmpi-1.6.4.tar.gz), a Message Passing Interface (MPI) library project. You can install it as follows,

  
  shell$ ./configure --prefix=YOUR_OPENMPI_DIRECTORY
  shell$ make all 
  shell$ make install
  
  
  
  

After finishing installation, set the environment variables. Add following environment variables to your ~/.bashrc,

• 
  #open MPI
  MPIDIR=YOUR_OPENMPI_DIRECTORY
  PATH=$MPIDIR/bin:$PATH 
  export MPIDIR  
  export LD_LIBRARY_PATH=$MPIDIR/lib:$LD_LIBRARY_PATH
  
  
  
  

Finally, 

• 
  shell$ source .bashrc
  
  
  
  

3 Procedure

1. Load ./pwmva_package.tar.gz, extract all files to your working directory. The text file “readme” contains the detail descriptions of the PWEMVA package and the instructions of running this package. Also the modules need to be loaded.

   
   tar -xzvf pwmva_package.tar.gz
   cd ./pwmva_package
   source sourceme
   cd ./src
   
   
   
   

2. Now you can compile the source codes. This step can be omitted if the user has not changed the code. First change the variable “DIR” in file “Makefile.config” to the directory where you put the pwmva package. Then type

   
   cd ./src/core
   make
   cd ../apps
   make pwmva_semb.x
   make pwmva_warp.x								
   
   
   pwmva_semb.x is the executable file for the code pwmva_semblance.f90, which calculates local shifts between plane-wave CIGs by semblance analysis. 
   pwmva_warp.x is the executable file for the code pwmva_warping.f90, which uses dynamic image warping to compute local shifts between CIGs.
   

3. Next you can run the code by typing

   
   cd ../../working
   make pwmva_semb
   make pwmva_warp							
   
   
   
   The input files such as initial velocity, plane-wave gathers, acquisition coordinate files are stored in “./pwmva_package/model/2D_models/mlayer/”. 
   

4. The inverted velocities using the semblance analysis and dynamic image warping are stored under the directories “./pwmva_package/results/2D_models/mlayer/pwmva_semb/” and “./pwmva_package/results/2D_models/mlayer/pwmva_warp/”, respectively.
5. To change the parameters and re-run the package for other data, please refer to the sections “parameters in pwmva_semblance.f90” and “parameters in pwmva_warping.f90”.