Hi Giulia, d1 and f1 are not SEG-Y standard fields, so anyone is (more or less) allowed put anything with any format in these fields (breaking seg-y standard, but it's common). They are SU only fields. If you don't know what has been coded there, you can use segyclean to erase any non seg-y standard field. If you wand to recover theses fields properly, you can try to remap them with the remap/byte option of segyread.

Regarding the time sampling of your data, keep in mind that SEG-Y rev0 (and so, SU) format has been designed for "heavy" seismics, with time sampling of 8, 4 or 2 ms, coded as integers. Maybe you will experiment roundup problems, with so small dt. As a workaround, you can change your time unit by multiplying dt by 1000 (ie using ms as time unit, and velocities in m/ms or accordingly).

Good luck D.

Le 26/06/2023 à 17:19, nickag64759@gmail.com a écrit :

Dear Sirs,

I have a seismic data sampled at micro-seconds.

I load 3 files with :

segyread tape=mySegy.sgy > mySegy.su

Then I used:

surange < mySegy.su

As you can see in the attached log files, the one called box31.log contains “strange” d1 and f1 values.

Please could you help me to understand why d1 and f1 are so big ?

The only one significant difference is that an01 and an31 are sampled at 33 micro-seconds while box31 is at 124 micro-seconds.

Thanks

Giulia

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