Alaska data

In the first part of the assignment, we will pick up processing of the Alaska line where he last left it, after the groundroll attenuation step. Figure 1 shows the shot gathers after groundroll removal by the Emc-Hammer team.

In this assignment, you will process the data further by applying surface-consistent amplitude balancing, velocity analysis, and stack.


rshots Figure 1. Alaska shot gathers after groundroll removal by Emc-Hammer.


arms,arms2 Figure 2. Trace amplitudes before (a) and after (b) removing the long-period offset trend.


scarms,adiff Figure 3. (a) Estimated surface-consistent trace amplitudes. (b) Difference with Figure 2b.


shot,receiver,offset,cmp Figure 4. Estimated surface-consistent factors.


ashots Figure 5. Alaska shot gathers after surface-consistent amplitude balancing.


stack0,stack1 Figure 6. (a) First attempt at NMO stack. (b) NMO stack after despiking by median filtering.


vpicks Figure 7. NMO velocity estimated by the automatic picker.


nmo2 Figure 8. Velocity analysis and NMO applied to a selected CMP gather.

from rsf.proj import *

# Shots after ground-roll removal by Emc-Hammer
Fetch('rshots.HH','alaska')
Flow('rshots','rshots.HH','dd form=native')

def plotshots(title):
    return '''
    pow pow1=1.5 | byte gainpanel=all pclip=90 |
    grey3 frame1=1000 frame2=55 frame3=30 title="%s"
    flat=n point1=0.7 point2=0.7
    ''' % title

Result('rshots',plotshots('Shots after Groundroll Attenuation'))

# Average trace amplitude
Flow('arms','rshots',
     'mul $SOURCE | stack axis=1 | math output="log(input)" ')
Result('arms','grey title=Log-Amplitude mean=y pclip=90')

# Remove long-period offset term
Flow('arms2','arms','smooth rect1=5 | add scale=-1,1 $SOURCE')
Result('arms2','grey title=Log-Amplitude clip=1.13')

# Integer indeces for different terms
Flow('shot','arms2','math output="(x2-44)/0.44" ')
Flow('offset','arms2','math output="(x1+5.225)/0.11" ')
Flow('receiver','arms2','math output="(x1+x2-44+5.225)/0.11" ')
Flow('cmp','arms2','math output="(x1/2+x2-44+5.225/2)*2/0.11" ')

nx = 96 # number of offsets
ns = 56 # number of shots
nt = nx*ns # number of traces

Flow('index','shot offset receiver cmp',
     '''
     cat axis=3 ${SOURCES[1:4]} | dd type=int | 
     put n1=%d n2=4 n3=1
     ''' % nt)

# Transform from 2-D to 1-D
Flow('arms1','arms2','put n2=1 n1=%d' % nt)

prog = Program('surface-consistent.c')
sc = str(prog[0])

Flow('model',['arms1','index',sc],
     './${SOURCES[2]} index=${SOURCES[1]} verb=y')

# Least-squares inversion by conjugate gradients
Flow('sc',['arms1','index',sc,'model'],
     '''
     conjgrad ./${SOURCES[2]} index=${SOURCES[1]} 
     mod=${SOURCES[3]} niter=30
     ''')

Flow('scarms',['sc','index',sc],
     '''
     ./${SOURCES[2]} index=${SOURCES[1]} adj=n | 
     put n1=%d n2=%d
     ''' % (nx,ns))
Result('scarms',
       '''
       grey mean=y title="Surface-Consistent Log-Amplitude" 
       clip=1.13
       ''')

Flow('adiff','arms2 scarms','add scale=1,-1 ${SOURCES[1]}')
Result('adiff','grey title=Difference clip=1.13')

size=dict(shot=ns,offset=nx,receiver=316,cmp=536)

f1 = 0
for case in ('shot','offset','receiver','cmp'):
    n1=size[case]
    
    Result(case,'sc',
           '''
           window n1=%d f1=%d | put o1=1 d1=1 | 
           graph title="%s Term" 
           label1="%s Number" unit1= label2=Amplitude unit2=
           ''' % (n1,f1,case.capitalize(),case.capitalize()))
    f1 += n1

Flow('ampl','scarms',
     'math output="exp(-input/2)" | spray axis=1 n=3000 d=0.002 o=0')
Flow('ashots','rshots ampl','mul ${SOURCES[1]} | cut n3=1 f3=49')

Result('ashots',plotshots('Shots after Amplitude Normalization'))

# Sort to CMPs

Flow('cmps mask','ashots',
     'shot2cmp half=n mask=${TARGETS[1]} | pow pow1=2')
Flow('mask1','mask','spray axis=1 n=1')

# Select one CMP

Flow('cmp1','cmps','window n3=1 f3=200')
Plot('cmp1','grey title=CMP')

Flow('vscan1','cmp1','vscan semblance=y half=n nv=151 v0=7 dv=0.1')
Plot('vscan1','grey color=j allpos=y title="Velocity Scan" ')

Flow('vpick1','vscan1','pick rect1=100')
Plot('vpick1',
     '''
     graph plotcol=7 plotfat=5 wantaxis=n wanttitle=n 
     yreverse=y transp=y min2=7 max2=22 pad=n
     ''')
Plot('vscanpick1','vscan1 vpick1','Overlay')

Flow('nmo1','cmp1 vpick1','nmo velocity=${SOURCES[1]} half=n')
Plot('nmo1','grey title=NMO')

Result('nmo','cmp1 vscanpick1 nmo1','SideBySideAniso')

# Apply to all CMPs

Flow('vscans','cmps mask1',
     '''
     vscan semblance=y half=n nv=151 v0=7 dv=0.1 
     mask=${SOURCES[1]}
     ''',split=[3,'omp'])
Flow('vpicks','vscans','pick rect1=100 rect2=20')

Result('vpicks',
       '''
       grey color=j scalebar=y barreverse=y mean=y 
       title="Picked NMO Velocity" 
       ''')

Flow('nmos','cmps vpicks','nmo velocity=${SOURCES[1]} half=n')

# Examine one CMP

cmp = 200 # !!! MODIFY ME !!!

Flow('vscan2','vscans','window n3=1 f3=%d' % cmp)
Plot('vscan2','grey color=j allpos=y title="Velocity Scan" ')

Flow('vpick2','vpicks','window n2=1 f2=%d' % cmp)
Plot('vpick2',
     '''
     graph plotcol=7 plotfat=5 wantaxis=n wanttitle=n 
     yreverse=y transp=y min2=7 max2=22 pad=n
     ''')
Plot('vscanpick2','vscan2 vpick2','Overlay')

Flow('nmo2','nmos','window n3=1 f3=%d' % cmp)
Plot('nmo2','grey title=NMO')

Result('nmo2','cmp1 vscanpick2 nmo2','SideBySideAniso')

# Stack

Flow('stack0','nmos','stack')
Result('stack0','grey title="First Stack" ')

Flow('stack1','stack0','despike2 wide2=10')
Result('stack1','grey title="Median-Filtered Stack" ')

End()