Read Prestack data

Note

cigsegy-v1.1.7 doesn’t support read a unsorted prestack gather in a convenient way. Prestack seismic gather will be supported in the next version of cigsegy.

However, this doesn’t mean that you cannot use cigsegy to read the unsorted prestack data. You can use get_trace_keys() function to analyze SEG-Y file’s trace headers and collect() to access data traces.

In SEG-Y file, the term CDP (common depth point) as used in this document is used as a synonym for the term CMP (common midpoint).

The differences between several gathers are shown in the following figure.

gather

In general, there are three keys to evaluate 3D prestack SEG-Y file: inline, xline or crossline, and offset.

Load 3D prestack SEG-Y (4D array)

Use cigsegy.metaInfo to scan the prestack file.

>>> cigsegy.metaInfo('3Dgather.sgy', iline=9, xline=21, offset=37)

Use cigsegy.fromfile to load 3D prestack file.

# geom can be obtained by `scan_prestack`
>>> d = cigsegy.fromfile('3Dgather.sgy', iline=9, xline=21, offset=37)
>>> d.shape
# (41, 482, 61, 1501) = (ni, nx, no, nt), no means number of offset

Load 2D prestack SEG-Y (3D array)

Load 2D prestack SEG-Y using the same approach as for 3D poststack data, i.e., use fromfile.

Set the cdp/line location as iline, and set offset location as xline.

>>> cigsegy.metaInfo('2Dgather.sgy', iline=9, xline=37)

>>> d = cigsegy.fromfile('2Dgather.segy', iline=9, xline=37)
>>> d.shape
# (1001, 120, 1500) = (n-line, no, nt), no is number of offset