Reading Dalhousie OBS data into Seismic Unix

The standard format for Segy data is Big endian, with an ebcdic header, and IBM floating point data. However, the Vista segy format used at Dal is a little endian, ascii header, IEEE 2 byte integer segy format. This makes it a bit more difficult to read into programs such as Claritas and Seismic Unix.

• Here is a method of reading this data into SU. Segyread is the program that reads the segy data, tape= is for the input file name, endian=1 is used becuase this file is little endian instead of the expected endian-ness. format=3 is used to define that the trace data is a 2 byte integer format.

segyread tape=obsdch1.sgy endian=1 format=3

• This can be combined with other su programs, such as determining the range of the trace header values:

segyread tape=obsdch1.sgy endian=1 format=3 | surange

• To convert this file to a standard SEGY file, use the following commands. segyhdrs is used to overwrite any values of the binary header that were read incorrectly.

segyread tape=input.sgy endian=1 format=3 > test.su
segyhdrs < test.su | segywrite endian=0 tape=test.sgy

• In Globe Claritas, the segy_analyser can be used to examine segy files. Remember to set it to little endian, ascii headers, and 2 byte integer trace data. Once it looks as it should, a job file can be created with the appropriate parameters to read in the segy file.