Changes

[[file:three-dimensional-seismic-method_fig1.png|300px|thumb|{{figure number|1}}(a) A CMP-stacked section. Copyright: a marine 3-D survey. (b) The corresponding 2-D migrated section. (c) The 3-D migrated section. (Data courtesy of Amoco Europe and West Africa, Inc.]]

[[file:three-dimensional-seismic-method_fig1.png|300px|thumb|{{figure number|1}}(a) A CMP-stacked section. Copyright: a marine 3-D survey. (b) The corresponding 2-D migrated section. (c) The 3-D migrated section. (Data courtesy of Amoco Europe and West Africa, Inc.]]

A typical marine 3-D survey is carried out by shooting closely spaced parallel lines (line shooting). A typical land or shallow water 3-D survey is done by laying out a number of receiver lines parallel to one another and placing the shot points in the perpendicular direction (swath shooting). Other recording geometries have also been used in acquiring 3-D data. Shooting in circles has been done in the Gulf of Mexico to delineate salt domes. Shooting around a lake or a topographic high to achieve subsurface coverage under the surface obstacle has also been tried.

A typical marine 3-D survey is carried out by shooting closely spaced parallel lines (line shooting). A typical land or shallow water 3-D survey is done by laying out a number of receiver lines parallel to one another and placing the shot points in the perpendicular direction (swath shooting). Other recording geometries have also been used in acquiring 3-D data. Shooting in circles has been done in the [[Gulf of Mexico]] to delineate salt domes. Shooting around a lake or a topographic high to achieve subsurface coverage under the surface obstacle has also been tried.

In marine 3-D surveys, the shooting direction (boat track) is considered to be the ''in-line direction'', whereas in land 3-D surveys, the receiver cable is along the in-line direction. The direction that is perpendicular to the in-line direction in a 3-D survey is called the ''cross-line direction''. In contrast to 2-D surveys in which line spacing can be as much as [[length::1 km]], the line spacing in 3-D surveys can be [[length::50 m]] or less. This dense coverage requires an accurate knowledge of shot and receiver locations.

In marine 3-D surveys, the shooting direction (boat track) is considered to be the ''in-line direction'', whereas in land 3-D surveys, the receiver cable is along the in-line direction. The direction that is perpendicular to the in-line direction in a 3-D survey is called the ''cross-line direction''. In contrast to 2-D surveys in which line spacing can be as much as [[length::1 km]], the line spacing in 3-D surveys can be [[length::50 m]] or less. This dense coverage requires an accurate knowledge of shot and receiver locations.