Editing Guide to madagascar programs (section)

==sfawefd2d==
{| class="wikitable" align="center" cellspacing="0" border="1"
! colspan="4" style="background:#ffdead;" | acoustic time-domain FD modeling 
|-
! colspan="4" | sfawefd < Fwav.rsf vel=Fvel.rsf sou=Fsou.rsf rec=Frec.rsf wfl=Fwfl.rsf > Fdat.rsf den=Fden.rsf ompchunk=1 ompnth=0 verb=n snap=n free=n expl=n jdata=1 jsnap=nt nq1=sf_n(a1) nq2=sf_n(a2) oq1=sf_o(a1) oq2=sf_o(a2)
|-
| ''file   '' || '''den=''' ||   || 	auxiliary input file name
|-
| ''bool   '' || '''expl=n''' ||  [y/n] || 	"exploding reflector"
|-
| ''bool   '' || '''free=n''' ||  [y/n] || 	free surface flag
|-
| ''int    '' || '''jdata=1''' ||   || 
|-
| ''int    '' || '''jsnap=nt''' ||   || 	save wavefield every *jsnap* time steps
|-
| ''int    '' || '''nq1=sf_n(a1)''' ||   || 
|-
| ''int    '' || '''nq2=sf_n(a2)''' ||   || 
|-
| ''int    '' || '''ompchunk=1''' ||   || 	OpenMP data chunk size
|-
| ''int    '' || '''ompnth=0''' ||   || 	OpenMP available threads
|-
| ''float  '' || '''oq1=sf_o(a1)''' ||   || 
|-
| ''float  '' || '''oq2=sf_o(a2)''' ||   || 
|-
| ''file   '' || '''rec=''' ||   || 	auxiliary input file name
|-
| ''bool   '' || '''snap=n''' ||  [y/n] || 	wavefield snapshots flag
|-
| ''file   '' || '''sou=''' ||   || 	auxiliary input file name
|-
| ''file   '' || '''vel=''' ||   || 	auxiliary input file name
|-
| ''bool   '' || '''verb=n''' ||  [y/n] || 	verbosity flag
|-
| ''file   '' || '''wfl=''' ||   || 	auxiliary output file name
|}

Below, we will demonstrate an example of a model with nx=nz=200 and dx=dz=4m (size: 800x800m). There are two layers: the first is 100x200 samples in (z,x), and the velocity is 1500m/s; the second layer has the same dimension, and the velocity is 3000m/s. The density is set to 1 for the whole grid. A source and a receiver are co-located at x=400 and z=100. The full wavefield for the entire model aperture will be saved every 10th time step.

<ol>
  <li>Velocity model:
<syntaxhighlight lang="bash">
sfspike > Fvel.rsf mag=1500,3000 nsp=2 k1=1,101 l1=100,200 d1=4 d2=4 \
label1=z label2=x n1=200 n2=200 o1=2 o2=2 unit1=m unit2=m
</syntaxhighlight>
</li>

<li>Density model:
<syntaxhighlight lang="bash">
sfspike > Fden.rsf mag=1 nsp=1 k1=1 l1=200 d1=4 d2=4 label1=z \
label2=x n1=200 n2=200 o1=2 o2=2 unit1=m unit2=m
</syntaxhighlight>
</li>

<li>Source position (x,z):
<syntaxhighlight lang="bash">
sfspike n1=2 nsp=2 k1=1,2 mag=400,100 o1=0 o2=0 > Fsou.rsf
</syntaxhighlight>
</li>

<li>Receiver position (x,z):
<syntaxhighlight lang="bash">
sfspike n1=2 nsp=2 k1=1,2 mag=400,100 o1=0 o2=0 > Frec.rsf
</syntaxhighlight>
</li>

<li>Source wavelet:
<syntaxhighlight lang="bash">
sfspike nsp=1 n1=2000 d1=0.0005 k1=200 | sfricker1 frequency=20 |\
sftransp > Fwav.rsf
</syntaxhighlight>
</li>

<li>Creating data at specified receiver + saving full wavefield every 10th step:
<syntaxhighlight lang="bash">
sfawefd2d < Fwav.rsf vel=Fvel.rsf sou=Fsou.rsf rec=Frec.rsf wfl=Fwfl.rsf \
den=Fden.rsf > Fdat.rsf verb=y free=y expl=y snap=y dabc=y jdata=1 jsnap=10
echo 'label1=z unit1=m label2=x unit2=m' >> Fwfl.rsf
</syntaxhighlight>
</li>

<li>View the wavefield movie:
<syntaxhighlight lang="bash">
< Fwfl.rsf sfgrey gainpanel=a pclip=99 color=j scalebar=y | sfpen
</syntaxhighlight>
</li>

<li>View a wavefield snapshot:
<syntaxhighlight lang="bash">
< Fwfl.rsf sfwindow f3=80 n3=1 |\
sfgrey pclip=99 color=j title='snapshot at t=0.4s' |\
sfpen
</syntaxhighlight>
</li>

<li>View the data recorded at the receiver:
<syntaxhighlight lang="bash">
< Fdat.rsf sfwindow |\
sfgraph title='Data recorded at receiver' unit2='' label2=amplitude |\
sfpen
</syntaxhighlight>
</li>
</ol>

[[Image:sfawefd_wfld.jpg|frame|center|sfawefd wavefield screenshot]]
[[Image:sfawefd_dat.png|frame|center|sfawefd data screenshot]]

Attention: time steps that are too large can result in numerical instability.