Which equipment provides a nadir-free, swath image of the seafloor by emitting side-by-side pings?

• A. Echo Sounder
• B. Multibeam Sonar
• C. Side-Scan Sonar
• D. Sub-bottom Profiler

Answer: (C)

This item tests how the geometry of sonar imaging determines what part of the seabed is captured. A nadir-free swath image is produced by side-scan sonar, which sends acoustic energy to the sides (port and starboard) of the survey platform, either simultaneously or in quick succession. This side-looking arrangement creates a continuous strip image of the seafloor along the vessel’s path, emphasizing texture and features, while the area directly beneath the vessel (the nadir) isn’t imaged effectively. In contrast, an echo sounder provides a single downward beam for depth, a multibeam system maps depth downward across a swath but still focuses below the craft, and a sub-bottom profiler looks beneath the seabed layers. Therefore, side-scan sonar is the instrument that yields a nadir-free, wide swath image by emitting side-by-side pings.