Topic:
How are seismic amplitudes stored in IES/IESX?

Description:
        

Solution:
IES

8 bit storage

Loading 32 bit data to IES 8 bit storage (such as SEGY tape loading into
IES system).  The data is processed trace by trace. Each 32 bit floating
point input trace is scanned for a maximum absolute value (MAXVAL). A
scalar (SCALAR) is then calculated , where SCALAR = MAXVAL / 127, which
is stored with the 8 bit IES output trace. On an 8 bit IES output trace,
there are 256 possible unique values (VAL) (Ranging from -128 to +127).
The amplitude of each floating point sample of the input trace
(FLOATAMP) is divided by SCALAR, such that VAL = FLOATAMP / SCALAR, and
a VAL is stored for each sample of the 8 bit output IES trace.  When an
IES trace is read back in an interpretation session, it is converted
back into a 32 bit format by multiplying each sample VAL by the stored
SCALAR for that trace, to form a "reconstituted" 32 bit value.  After
this process is complete for each trace, the trace will contain sample
values across the same range of floating point numbers as the original
32 bit SEGY data, but limited to a maximum of 256 unique values.

16 bit stsorage

Loading 32 bit data to IES 16 bit storage (such as SEGY tape loading
into IES system). The data is processed trace by trace. Each 32 bit
floating point input trace is scanned for a maximum absolute value
(MAXVAL).  A scalar (SCALAR) is then calculated, where SCALAR = MAXVAL /
32768, which is stored with the 16 bit IES output trace. On a 16 bit IES
output trace, there are 65536 possible unique values (VAL) (ranging from
-32768 to +32767). The amplitude of each floating point sample of the
input trace (FLOATAMP) is divided by SCALAR, such that VAL = FLOATAMP /

SCALAR, and a VAL are stored for each sample of the output 16 bit IES
trace.  When an IES trace is read back in an intrepretation session, it
is converted back into a 32 bit format by multiplying each VAL by the
stored SCALAR for that trace, to form a "reconstituted" 32 bit value.
After this process is complete for each trace, the trace will contain
sample values across the same range of floating point numbers as the
original 32 bit SEGY data, but limited to a maximum of 65536 unique
values.

IESX

8 bit and 16 bit storage in IESX work similarly to IES, with one
difference.  Instead of scanning purely for a trace absolute maximum to
calculate the scalar, the minimum and maximum actual values on the trace
are determined, and the data compression is done only between those two
values. To illustrate this difference, assume a trace with original
values that range between -25,000 and +40,000. IES would have found the
absolute maximum value (40,000) and would have calculated a scalar to
fit the signed ranage of numbers -40,000 to +40,000.  IESX records the
amplitude range of -25,000 to +40,000 and scales the data precisely
within that range.

Despiking

There is no despiking in IES.  In IESX anything over 50 times the mean is
clipped.  The user has no control over this.





Last Modified on: 03-DEC-98