Figure 2.Section view of Earth layering that is to be imaged. A 3-D designer needs to know two critical depths: (1) depth Z₁ of the shallowest reflector that has to be Imaged, and (2) depth Z_tar of the primary target to be studied. If multiple targets exist at various depths, then Z_tar should be defined as the depth to the deepest target. The shallow target depth Z₁ controls the source-line and receiver-line spacings, which should be no larger than the offset distance X_min shown here. The deep target depth Z_tar defines the physical size of the recording swath, which should span an area having a width of about 2X_max in both the in-line and cross-line directions.