SEG-Y Key Field Locations

Use the SEG-Y Key Field Locations dialog to verify or provide the critical information that will allow the selected SEG-Y file to be read properly. In most cases, the correct fields will be automatically detected and those values displayed.

After this dialog is closed, the entire file will be scanned to determine the data ranges.

SEG-Y Key Field Locations dialog options

Byte order	Specify the byte order of the input file: "Big endian" or "Little endian." The default is "Big endian." This must be correct in order for the file to be read beyond the text header.
Samples per trace	Specify the number of samples in each data trace. In most cases, the correct header location for this information will be selected automatically and the correct value shown.
Sample interval	Specify the vertical sample spacing for the trace data. This value is almost always stored in thousandths of the true units (i.e. stored as µs (1000x larger) when all other values are stored as ms). In most cases, the correct header location for this information is selected automatically and the correct value shown.
First sample at	Specify the delay recording time for the first sample. If the recording of the seismic signal is delayed after the shot, that delay time (or distance) will be recorded in the trace header. This has the effect of shifting the seismic data upward (negative values) or downward (positive values) and is sometimes incorrectly referred to as a "datum shift." You may override the default value.
Last sample location	This read-only field shows the calculated location of the last sample in the trace.
Trace data format	Select the trace data format from the drop-down list. This should be defined in the Binary Header and the correct format automatically selected, but you may change it.
[Text Header]	Click this button to view the Text Header in a read-only window.
[Binary Header]	Click this button to view the Binary Header in a read-only window.
[Trace Viewer]	Click this button to show the Trace Viewer in a separate dialog, which allows you to view the trace headers data for any trace.

Application Notes

The SEG-Y Standard(s) specify the locations and format of the information in the file. In most cases, the correct locations will be detected and, if available, the correct values displayed. However, values may be incorrect or missing or the trace format incorrect. You may change the Binary or Trace Header locations that are used for most values, and in most cases you may enter your own value if required.

Vertical Units

If the vertical axis is time, all values in the file, with the exception of the sample interval, will be in milliseconds (ms); the sample interval is expected to be given in µs. If the vertical axis is depth, the vertical units will be meters or feet, depending upon the unit system specified in the Binary Header, and the sample interval will be in milli-meters or milli-feet. The value is essentially biased by 1000x so that fractional values may be stored as an integer. In some cases the sample interval may not be biased in this way and you may change the units drop-down to reflect this.