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Increases in Dynamic Range Through Trace Dependent Scaling in IESX
Keith Woollard - GeoCom Services Australia Pty Ltd
Introduction “The unique disk-efficient seismic data
storage procedure preserves the dynamic range of the Data”• How true is this statement?• How does it work?• What are the benefits?• What possible problems exist?• How can it be improved?
Testing Procedure32 bit
Input SEG-Y
8 & 16 bitSeisWorks and IESX
load
SEG-Y export(manual rescale for
SeisWorks data) DifferenceVolumes
PercentagedifferenceVolumes
Arithmetic Difference
RMS of difference 8 bit 16 bit
Conventional 24.4 0.25
IESX 18.2 0.07
Input data RMS = 348
Amplitudes of each trace analysed
How Does it Work?
+127-127
These values set to F.S.D.
Min and max amp found for each trace
Traces sorted into 2n bins
How Does it Work? One scalar pair calculated for each trace Scalar stored along with trace Scalar can be reversed by software Other systems have one scalar per
line/load/survey and require user to document value
When does it have problems? In the presence of a strong time variant
amplitude gradient
Percentage error per sample
Time Variant Amplitude Issues
Trace dependent scalar ideal for spatial amplitude variation
0
10
20
30
40
50
60
0 1000 2000 3000 4000 5000 6000
Time
Error
Not suited to temporal variations
Suggestions:• 1 scalar per N samples • N scalar per trace
Single large amplitudes Typical seismic data has one or two sample
much larger than the rest In test dataset, second largest amplitude on
each trace is 82% of largest. Third largest is 54%
True amplitude histogram Histogram after AGC
Single large amplitudes Thus to preserve two samples, we are
halving the dynamic range of the rest. For old/on-shore/scanned data, single bad
samples will destroy whole trace Significantly better amplitude binning could
be obtained by using second or third largest amplitude
No problem for well-modulated data No need to run de-spike filters
Summary Marginally better amplitude representation
than conventional single scalers for 8 bit Significantly better amplitude representation
than conventional single scalers for 16 bit Easier data loading Seamless amplitude recovery Not perfect, especially when loading to 8 bit Two improvements possible
• time gated scaling• “second largest” amplitude method