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Max
Value - Overview
Max value questions usually concern the following:
Amplitudes may be weak because some of the traces examined to extract
the estimated max value contained anonymously high amplitude spikes. The estimated max value is preserving
these spikes at the expense of all other amplitudes in the file.
Click <Chart Max Values>
and select a value that will provide appropriate amplitudes in your zone
of interest while clipping amplitude spikes.
Amplitudes are clipped because the traces examined by the wizard to
determine the estimated max value were dead traces or simply weaker
amplitudes that do not properly reflect the highest amplitudes in the
file.
Use <Chart Max Values>
to examine the entire file. Choose a larger max value and click <OK>. If data amplitudes now seem
to be too low, see Weak Amplitudes
above.
If you have gone to special effort to process your data to maintain
relative amplitudes between SEG-Y files, you will want to set the same max value for
all files in the batch. These files are not likely to have high amplitude
spikes so, a good rule of thumb is to set the max value for all files
to the max value of the file with the largest amplitude.
Use the <Chart
Max Values> function to view amplitude statistics for all files.
Select one max value and apply it to all files in the set.
Statistical or computed attribute data can be written to SEG-Y file
format and imported to WinPICS.
Attribute values are written as amplitudes in these SEG-Y files. Special
steps must be taken when scaling attributes with fixed value ranges.
First, it is useful to understand how max value scaling works mathematically.
The absolute value selected for max value is set equal to 32767. All samples
with an absolute value greater than the selected max value are clipped.
Values with absolute values less than the max value are scaled proportionally.
This allows WinPICS to work with
8, 16 and 32 bit data.
To maintain meaningful attribute values you must select a factor of
32767 for the max value.
For example: If you have attribute data with values of plus or minus
180 degrees, select 327.67 as your max value.
When 327.67 is set equal to 32767 it is multiplied by 100. The
values in your file will be multiplied by 100 too. This means that a value
of 180 will be represented as 18000. This method provides maximum dynamic
range and meaningful values for mapping.
Max Value Facts
- Max value scaling is applied on import but can
be modified at a later time using Change Max Value or viewed using Display
Max Value Statistics.
- If your import destination format is 32-bit, no
amplitudes are clipped in the file. The max value scalar is simply applied
each time the file is accessed. While traces may be displayed as clipped
on screen, the original amplitudes are preserved in the file.
- If your import destination format is 8- or 16-bit,
the max value scalar is
applied during the reformat process. Any amplitude above the max value
will be clipped when you convert your 32-bit data to a 8- or 16-bit file.
8- or 16-bit may be scaled in View
Max Value Statistics but this function can not undo clipping. A clipped
file must be re-imported to restore clipped values.
- Problems with amplitude scaling may not need to
be fixed with max value. Once data has been imported it may be scaled
by the interpreter using Tie
Seismic.
How to Solve Scaling Problems
Most max value scaling problems can be avoided by using <Chart
Max Values> to select reasonable scaling values.
Often you will want to maintain the highest amplitude range possible
without losing the critical amplitudes over your zone of interest. Normally,
using the estimated max value
for each file will accomplish this. In some cases, the traces scanned
to estimate the max value are
not representative of your entire SEG-Y file.
In this case, you will need to examine the file and make a decision
about which amplitudes you want to preserve and which you want clipped.
The max value function is used
to compute a scale factor applied to 32-bit data for viewing and plotting.
The goal is to find a scale factor that displays the data strongly without
clipping valid high amplitudes.
What do you want to do?
Weak Amplitudes