Trace Headers and Windowing Data
When seismic traces are in SEG-Y format, the SU trace format, and many other formats, the beginning of every trace, the trace header, has information about the trace. You can think of these as slots of information above the data part of the trace. The data part is the time-amplitude series that we see in a seismic display.
Trace header information might include the trace number and the offset of the trace (for shot or CMP gathers). In an SU seismic data set, the number of trace header slots is the same to ensure that every trace in a data set has the same length (in terms of bytes of storage).
SU doesn't call them headers; it calls them keys. The following table lists some SU keys.
You can use program surange to learn which keys are in a data set and the range of their values (the largest and smallest values). Now that you have run script myplot.sh (Section 2.4), use program surange to examine the trace headers of the .seismic file. Enter:
The output (screen display) is:
This synthetic data set has 32 traces. Only five of its keys (trace headers) have non-zero values. The minimum value of trad and tracr is 1; the maximum value of trad and tracr is 32. This is not surprising since there are 32 traces in the data set. We can suppose that the traces are numbered in sequence, 1 to 32. Surprisingly, all traces have the same offset: 400.