Geoscience Reference
In-Depth Information
Fig. 3.9
Same section as fig. 3.8 , wiggle trace display.
Another issue that the interpreter needs to be aware of is the effect of the limited
dynamic range of the display and perhaps of the underlying data. The number of possible
different amplitude levels that can have different colours assigned to them in a screen
display is typically only 256 (8-bit resolution). This gives an adequate visual impression,
but is much less than the dynamic range of the original seismic data. If the original data
had a range of amplitude values from, say,
13 000 to
+
13 000 then the simplest way
to convert it to the range from
128 required for the display would be to divide
the seismic amplitudes by 100 and then round them to the nearest integer. However, the
strongest amplitudes might be in a part of the dataset quite different from the one that
we want to study; maybe we are interested in looking at subtle changes in reflection
strength of a weak reflector, whose amplitude is only, say, + 1000 in the original data.
Scaling would reduce this to a value of around 10, and the effect of rounding to the
nearest integer becomes serious: changes in reflection strength would be quantised in
10% jumps. The solution to this problem is to adjust the scaling of the display; the
available display amplitude range of 127 to + 128 is used for seismic amplitudes
from C to + C , where C is a clip level set by the user. Any seismic amplitudes outside
this range are simply set to 127 or + 128 depending on the sign. By choosing the clip
127 to
+
 
Search WWH ::




Custom Search