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Figure 4 – Recording swath designed to image a deep target at depth Ztar. 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 Ztar. 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 Ztar; others set one of the widths EF or EG equal to Ztar. Either option is satisfactory. At least one dimension of the recording swath must be approximately twice as long as depth Ztar 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.