Page 251 - Acquisition and Processing of Marine Seismic Data

242 5. PREPROCESSING

5.1 DEMULTIPLEXING

Raw seismic data is recorded as samples in
rows, in which the amplitude samples digitized
at the same recording time at each individual
channel are recorded in the same data row into
the tapes or hard disks. This results in a data vol-
ume consisting of the first sample of first channel,
first sample of second channel, first sample of
third channel, etc. (Fig. 5.2A). Seismic data
should be rearranged so that it consists of data
FIG. 5.1 Preprocessing steps for prestack seismic data columns: all amplitude samples of first channel,
conditioning. all amplitude samples of second channel, etc.
This arrangement is known as demultiplexing
and mathematically it is a transpose process in
which each row is transposed individually so
routinely applied to raw seismic data, demulti- that the data volume consists of data columns,
plexing, f-k dip filter or shot-channel edit may each containing amplitude samples of one partic-
not be needed, according to the specifications, ular channel (Fig. 5.2B). Today, modern seismic
quality and the noise content of the input data recording systems perform demultiplexing
seismic dataset. In addition, the application before storing the data onto the disk or tape
order may also differ from one processor to drives, and therefore, depending on the specifica-
another, depending on the requirements of the tions of the recording unit, demultiplexing may
input data. not be required during data processing.

FIG. 5.2 Schematic representation of demultiplexing on a shot gather with six traces. (A) Sorting of the amplitude samples
of raw seismic data set during acquisition, and (B) amplitude samples after demultiplexing.