SEGY Exchange Format

Despite its age, the SEGY data exchange format remains popular. Originally designed for 1/2 inch tape, it has evolved into a disk format as well. It consists of the following:

Where the Seismic Unix (SU) program segywrite uses a pipe to the dd program for the conversions between ASCII and EBCDIC, the BSU program bcnv.c uses library functions found in bsu-3.0.2/src/libIBM to do the conversions. The requisite functions were downloaded from IBM in the original EBCDIC, converted to ASCII and then edited to make the small static library libibm.a.


The reel headers are then followed by (trace header, data) signals. These are encoded as follows for each signal:

Program bcnv is used to convert between SEGY (exchange format above) and BSEGY (used by the BSU software). If you really have data on tape, recommend that you use Seismic Unix (SU) programs, segyread and segywrite. The program, bcnv, has been updated. The current version of bcnv will create SEGY data that can be read by SU program segyread. The reverse direction is also true. That is, SEGY data created by SU program segywrite can be read by BSU program bcnv. This has been tested successfully on 4 byte floats.