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(a)gmail.com a écrit :