Topic:
How to fix blank time slices.

Description:
The time slices are blank and in 'report' in data manager, amplitude values 
are inconsistant.

Solution:
When time slices display blank, this is an indication of the vertical volume of 
seismic contains a spike which is skewing the amplitude range. Time slices use
the survey rms for display. Check the seismic display with 'survey' rms - this
will also be a very high number.
 
There are 2 ways to handle this. You can either find the spikes and null the
trace out or reload the data with clipping applied.
 
To find the spikes:
 
 1.)  Application > Computation Manager 
 2.)  Computation Manager window comes up, press the 'OK' button
 3.)  Select Mappable Seismic Statistics under "Available operations" (at the    
       very top)
 4.)  Select RMS amplitude from the menu, then 'OK'
 5.)  Back at the ComputationManager window press the 'Survey' button at the top
 6.)  Pick your survey, Input class/Output class then 'OK'
 7.)  Back at the ComputationManager window press the 'Start' button
 8.)  After Computation Manager has finished, go to Application >
       Interpretation > Basemap
 9.)  Post > Interpretation
10.)  Select horizon 'linevolume_stat' and the appropriate attribute.
11.)  Spike(s), will appear as anomalous values.
        When you find the spike(s), display the seismic line and note the line, CDP, 
        and trace numbers.
12.)  To 'Null' the spikes, select Application > Data Manager > Seismic > Copy.
13.)  Select the Survey and Input class, for the spiked data.
        Toggle the 'Copy' button to 'Null data', press the 'Change Area' button,   
        "Selection type" can be toggled to 'Trace', 'CDP' or 'SP' 
        Set the appropriate range eg,if the spike is on trace was 345, then set the 
        trace min/max to 345, then 'OK'. 
14.)  Back at the "Seismic volume copy" window, press the 'Generate' button at
        the bottom. This will update the Input class, it does not create a new class.
15.)  You will need to run in IESX_UTIL, option 32. 'Update seismic volume 
        statistics' to recalculate the seismic amplitude statistics. Refer to the
        'How to' in IESX_UTIL on this procedure.
16.)  Verify the result for survey rms by comparing Seismic report which is 
        static and Report - Amplitude Statistics (which computes on the fly)...
        should be the same. 
       
 
Reload the data with clipping on:
 
 1.)  Application > Data Manager > Seismic > Load Seismic, click the       
       'Define input format ...'  button
 2.)  Set the byte location of Auxilliary value (A1) to be the cdp number
       eg. Auxilliary value (A1) = byte 21, IBM (32 bit int.)
 3.)  Under the "Key parameter source" toggle  CDP to 'Expression'
       then press the button 'Shot point/CDP expression...'
 4.)  Define CDP =A1;editval(-100,100,0,0,10000,1)

 
In this example the expression will relace values outside the range of -100 to 
100 with 0, for a max of 10000 samples and will not produce a listing.
Modify these values as required.
 
EDITVAL has the following parameters and can be used as an expression.
It has only one required argument but you can specify up to five optional 
arguments for more control.
 
EDITVAL (clipa[,clipb[repla[,replb[num[,notify]]]]])
 
clipa: clip value (If only 1 argument, then this is the +/- clipval
EDITVAL (1000000) will replace any value outside of (-1000000;+1000000) with 0
 
clipb: clip value (Unclipped range is clipa:clipb
EDITVAL (-99, 99) will replace any value outside of (-99:+99) with 0

repla: value to replace clipped values. Default is 0,0 if nor replb, then this 
is the +/- replaceval
 
replb: value to replace clipped values, clipa replace with repla, clipb is replace wtih replb
EDITVAL (-77, 77, 75) will replace an value less that -77 with 75 and replace an
y value greater than +77 with +75
EDITVAL (-60, 60, 0, 60) will replace any value less than -60 with 0.0 and 
replace any value greater than 60 with 60.
 
num: maximum number of values to clip (default is all)
EDITVAL (-60, 60, 0, 60, 2) same as above but will only replace the first two 
values that are out of range
 
notify: 0=no, else generate listing line of clip counts (default is 0, no listing line)
EDITVAL (-60, 60, 0, 60, 2,1) same as above, but generates line listing for any 
trace that was clipped, giving the count of the number of clips
 
Use the variable number of clips parameter:
EDITVAL (-60, 60, 0, 60, A1*1000, 1) setup up to clip but if A1 is zero then no 
clipping is done. This can be used to turn clipping on/off based on some variable.




Last Modified on: 01-OCT-98