Editing Guide to madagascar programs (section)

===SEG-Y Trace Headers===
In the SEG-Y standard, only the first 180 bytes of the 240-byte trace header are defined; bytes 181-240 are reserved for non-standard header information, and these locations are increasingly used in modern SEG-Y files and their variants. The standard provides for a total of 71 4-byte and 2-byte predefined header words. These 71 standard words have defined lengths and byte offsets, and only these words and byte locations are read using <tt>segyread</tt> and output to the RSF header file with the <tt>tfile=</tt> option. The user may remap these predefined keywords to different byte offsets.