Exchange Formats

These are formats meant to publicly defined so that users may exchange data regardless of what processing software they may ordinarily use. Examples would include SEGY, SEG-2, Bison, and SEG-D. The professional society, Seismic Exploration Geophysicists (SEG) has created all of these except the Bison format which was developed by makers of an engineering seismograph. For example, SEG-2 was developed for personal computers, Pullan (1990). There are other types of data exchange formats. For example, for Computer Aided Drafting, there is DXF (data exchange format). BSU software also can convert header information into DXF format which can then be used to make base maps.

Bison format is really just the format output by Bison seismographs. It can be integer or floating point. However, the floating point is extremely unusual, and I know of no other software than BSU which can process the Bison floats correctly. In particular,

   Float 16 bit 2's complement mantissa, 4 bit exponent normalized float
   generated from 32 bit internal fixed format standard instrument storage
   format. Transmitted as follows: in groups of 5 words

   LSbyte of first sample mantissa
   MSbyte of first sample mantissa
   LSbyte of second sample mantissa
   MSbyte of second sample mantissa
   LSbyte of third sample mantissa
   MSbyte of third sample mantissa
   LSbyte of fourth sample mantissa
   MSbyte of fourth sample mantissa

   Exponent word:
     Least significant nibble of first byte for fourth word.
     Most significant nibble of first byte for third word.
     Least significant nibble of second byte for second word.
     Most significant nibble of first byte for first word.
     
One must Check to see if 4 bit exponent is greater than 7 
(implies negative exponent in that case).  Decode to negative
4 bit number using assumption of 2's complement

If one has a choice, I recommend integer formats for recording and exchange. For exchange, I have used SEGY