Figure 4. Recording swath designed to image a deep target at depth Z_tar. The swath is the area enclosed by rectangle ABCD, and the active source stations for the swath are all of the stations on source lines S₁ through S₉ that are between receiver lines R₅ and R₆ (the shaded strip). The fundamental requirement is that there must be several source-receiver offsets that are approximately twice the magnitude of target depth Z_tar. This offset condition exists when (1) the active source stations are on source lines S₁ and S₂ and the receiver stations between source lines S₈ and S₉ are active, or when (2) the active source stations are on source lines S₈ and S₉ and the receiver stations between source lines S₁ and S₂ are active. Some designers set diagonal distance EC equal to Z_tar; others set one of the widths EF or EG equal to Z_tar. Either option is satisfactory. At least one dimension of the recording swath must be approximately twice as long as depth Z_tar to the primary (or deepest) target. The number and length of receiver lines inside the swath are controlled by the source-line and receiver-line spacings and by the channel capacity of the recording system.